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Strategies for Pollutant Monitoring in Museum Environments

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This project is a collaboration between the Swedish National Heritage Board (Riksantikvarieämbetet) and Nationalmuseum in Stockholm, Sweden. It focuses on monitoring indoor pollutants in museum environments. Pollutants can adversely react with collection objects in large spaces such as galleries and in smaller enclosures like display cases or storage containers. It is common practice to measure indoor air quality for human health and safety, but the pollutants that negatively react with cultural heritage are often different from those that affect humans. It is therefore important for museums to understand which pollutants are most significant and how to monitor for these compounds. This report will review existing literature on pollutant monitoring in museum environments and present an example monitoring project through a case study with Nationalmuseum. The literature review will discuss important pollutants for cultural heritage collections, existing pollutant monitoring techniques that can be tailored for museum environments, and some notes on material choices to reduce harmful pollutants. Included in the Appendices are a list of standards related to air quality and monitoring as well as a chart listing some existing devices for air quality measurements.
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Strategies for Pollutant
Monitoring in Museum
Environments
RIKSANTIKVARIEÄMBETET
Swedish National Heritage Board
P.O. Box 1114
SE-621 22 Visby
Tel +46 8 5191 80 00
www.raa.se
registrator@raa.se
Riksantikvarieämbetet 2019
Strategies for Pollutant Monitoring in Museum Environments
Authors: Elyse Canosa & Sara Norrehed
Copyright according to Creative Commons licens CC BY,
unless otherwise stated.
Terms on https://creativecommons.org/licenses/by/4.0/deed.en
Strategies for Pollutant Monitoring in Museum Environments 3
Table of Contents
Contributors ................................................................................ 4
Svensk sammanfattning ............................................................. 5
Abstract ....................................................................................... 6
Introduction ................................................................................. 7
Background ............................................................................... 10
Gaseous pollutants in the museum environment ............................. 10
Sulfur dioxide (SO2) .................................................................. 10
Ozone (O3) ................................................................................ 11
Nitrogen oxides (NOx) ............................................................... 11
Reduced sulfur gases ............................................................... 11
Volatile organic compounds ..................................................... 12
Other pollutants ........................................................................ 13
Guidelines for pollution levels ................................................... 14
Indoor vs. outdoor pollutants .................................................... 17
Selecting materials for storage and display ...................................... 19
Tools for pollutant monitoring ........................................................... 20
Air samplers vs. dosimeters ..................................................... 21
Passive vs. active devices ........................................................ 24
Direct-read vs. laboratory analyzed devices ............................ 26
Qualitative vs. quantitative devices .......................................... 30
Sensor networks ....................................................................... 30
Pollution monitoring practices in museums ...................................... 31
Mitigation techniques ........................................................................ 34
Pollutant monitoring at Nationalmuseum ....................................... 36
Motivation .......................................................................................... 36
Materials and methods ..................................................................... 36
Results and discussion ..................................................................... 41
Conclusions .............................................................................. 47
Disclaimer .................................................................................. 49
Appendix I .................................................................................. 50
Flow chart: examples of commercial air monitoring devices ............ 50
Appendix II ................................................................................. 52
Table of commercial air monitoring devices ..................................... 52
Appendix III ................................................................................ 56
Standards for indoor air quality measurements ................................ 56
References ................................................................................. 58
Strategies for Pollutant Monitoring in Museum Environments 4
Contributors
The contents of this report were designed and written by Elyse Canosa with
support from Sara Norrehed, both project advisors at the Swedish National
Heritage Board (Riksantikvarieämbetet). Vital collaborators at Nationalmuseum
include Kriste Sibul, Veronika Eriksson, Carolyn Jessen, Charlotta Bylund Melin,
and Joakim Werning, who all aided with the setup and execution of the pollutant
monitoring case study. Finally, Marta Segura Roux at the Swedish Environmental
Research Institute (IVL) provided valuable practical support throughout the
project.
Strategies for Pollutant Monitoring in Museum Environments 5
Svensk sammanfattning
Denna rapport beskriver metoder att undersöka och övervaka luftföroreningar
inomhus i en museimiljö. Luftföroreningar i en museimiljö kan komma utifrån,
från konstruktionsmaterial inomhus eller från museiföremålen själva. Dessa
luftföroreningar kan orsaka skador på föremål genom att påskynda den kemiska
nedbrytningen och orsaka till exempel försprödning, korrosion, missfärgning och
sprickbildning. Skadliga luftföroreningar kan förekomma både i stora utrymmen
som utställningssalar, eller i små täta utrymmen som montrar och förvaringslådor.
Det är vanligt att mäta luftkvaliteten inomhus för människors hälsas skull, men de
luftföroreningar som påverkar kulturarvsföremål skiljer sig från de som påverkar
människor. Denna rapport sammanställer befintlig litteratur kring
luftkvalitetsövervakning i museimiljö och presenterar en fallstudie som utförts i
samarbete mellan Riksantikvarieämbetet och Nationalmuseum under 2018.
Litteratursammanställningen belyser luftföroreningar som är betydande för
kulturarvet, tillgängliga analysmetoder som kan skräddarsys för museimiljöer samt
diskuterar i korthet lämpliga materialval för att minska skadliga föroreningar. En
lista över standarder som rör luftkvalitet och luftkvalitetsövervakning samt en
tabell med provtagare för luftkvalitetsmätningar finns sammanställd i appendix.
Mellan 2013 och 2018 genomfördes en omfattande renovering av
Nationalmuseum. I samband med renoveringen installerades nya montrar och
podier för att visa föremål från samlingarna. Eftersom konstruktionsmaterial kan
avge emissioner som kan vara skadliga för kulturarvsobjekt var det därför viktigt
att undersöka om de nya materialen skulle kunna påverka Nationalmuseums
samlingar.
Luftkvalitetsövervakning användes som en metod för att undersöka luftkvaliteten
på Nationalmuseum i öppna salar samt i slutna montrar. Studien utfördes genom att
placera provtagare som mätte flyktiga organiska ämnen (VOC), ättiksyra, myrsyra,
aldehyder, vätesulfid, svaveldioxid, kväveoxider samt ozon. Provtagarna som
användes är små, lätta att hantera och kräver inte tillgång till egen analysutrustning
eller andra förkunskaper. Resultatet av luftövervakningen ökar kunskapen om
samlingens miljö, vilket vidare bidrar till att kunna identifiera risker och ta mera
välunderbyggda beslut om objektens bevarande.
Kortare, praktiska rådgivningsblad på svenska har utformats utifrån denna rapport
och ingår i Riksantikvarieämbetets serie med Vårda väl-blad, www.raa.se/vardaval.
Strategies for Pollutant Monitoring in Museum Environments 6
Abstract
This project is a collaboration between the Swedish National Heritage Board
(Riksantikvarieämbetet) and Nationalmuseum in Stockholm, Sweden. It focuses on
monitoring indoor pollutants in museum environments. Pollutants can adversely
react with collection objects in large spaces such as galleries and in smaller
enclosures like display cases or storage containers. It is common practice to
measure indoor air quality for human health and safety, but the pollutants that
negatively react with cultural heritage are often different from those that affect
humans. It is therefore important for museums to understand which pollutants are
most significant and how to monitor for these compounds. This report will review
existing literature on pollutant monitoring in museum environments and present an
example monitoring project through a case study with Nationalmuseum. The
literature review will discuss important pollutants for cultural heritage collections,
existing pollutant monitoring techniques that can be tailored for museum
environments, and some notes on material choices to reduce harmful pollutants.
Included in the Appendices are a list of standards related to air quality and
monitoring as well as a chart listing some existing devices for air quality measurements.
Between 2013 and 2018, Nationalmuseum underwent a large renovation in which they
installed new display structures using a variety of materials. Such products will
naturally emit volatile compounds and it is important to understand how such
emissions will affect Nationalmuseum’s collection. Combined with natural outdoor
pollution that can ingress into the museum, indoor material emissions can create a
harmful environment for collection materials. Pollutant monitoring was therefore used
as a method to study the air composition inside Nationalmuseum galleries and display
cases, and to determine the presence of any potentially harmful emissions. To execute
this study, passive air samplers were used to collect volatile organic compounds
(VOCs), acetic acid, formic acid, aldehydes, hydrogen sulfide, sulfur dioxide, nitrogen
dioxides, and ozone. The samplers were small, easy to use, and did not require an in-
house laboratory. Such a process could easily translate to other institutions interested in
air quality monitoring. The information obtained through this project will provide
Nationalmuseum conservators with greater knowledge about the collection
environment, ultimately helping to identify risks and preserve the museum’s collection.
With Nationalmuseum as a case study, the goal of this project is to provide
museums with existing information about potentially harmful pollutants and ways
in which these pollutants can be monitored. This report is intended for readers with
an interest in emissions analysis and pollutant monitoring. This can include (but is
not limited to) museum conservators, conservation scientists, collection managers,
preservation specialists, and archivists. Some technical knowledge about air
chemistry and analytical techniques is helpful in interpreting the results from the
case study, but is not necessary for the literature review. Shorter, practical, and
non-technical documents in Swedish have been adapted from this report and are
available through Riksantikvarieämbetet’s Vårda väl-blad series, www.raa.se/vardaval.
Strategies for Pollutant Monitoring in Museum Environments 7
Introduction
Pollutant monitoring is an important aspect of preventive preservation in cultural
heritage environments. Cultural objects can react adversely to atmospheric
pollution and undergo corrosion, fading, embrittlement, and other forms of
deterioration. Unlike humans, objects do not have inherent filtration or repair
mechanisms to combat the effects of pollution. Additionally, we expect cultural
heritage to have extensive lifespans, during which they must be properly protected
from deterioration. There are a number of pollution monitoring tools and methods
developed for health and human safety applications. Such tools can be used in
cultural heritage environments, but do have notable limitations. Cultural objects
can visibly react to very low pollutant concentrations, lower than are typically
measured in health and human safety studies. For example, silver corrodes when
exposed to hydrogen sulfide gas concentrations on the parts per trillion (ppt) level
(Watts 2000). Comparatively, ambient air levels of hydrogen sulfide from natural
sources are much higher, with estimated concentrations between 0.1 and 0.3 parts
per billion (ppb) (Chou 2003, US EPA 1993). Many existing tools manufactured
for quick and easy environmental monitoring may therefore not be sensitive
enough for cultural heritage applications. In addition, there are some atmospheric
gases, such as acetic acid, which are of less concern to human health but have
documented effects on cultural heritage (Tennent and Baird 1992, Niklasson, et al.
2008, Mattias, Maura and Rinaldi 1984, Tetreault, Sirois and Stamatopoulou
1998). This can be problematic when museums purchase materials that are not
tested for their propensity to emit acetic acid.
The differences between outdoor-generated pollution and indoor-generated
pollution are as important in cultural heritage as they are in human health and
safety. Major outdoor pollutants that pose risks to cultural objects are sulfur
dioxide, nitrogen dioxide, nitrogen oxide, ozone, and hydrogen sulfide (Thomson
1986, Grzywacz 2006, Tétreault 2003). While buildings offer some protection from
such gases, pollutants can enter the indoors through holes and cracks in the
building as well as windows, doors, and the ventilation system (Rhyl-Svedsen
2007). Indoor-generated pollutants can be produced by construction materials
(paints, boards, flooring), indoor activities (cleaning, cooking, heating), people, and
other objects. Major indoor pollutants that pose risks to cultural objects are acetic
acid, formic acid, acetaldehyde, formaldehyde, hydrogen sulfide, carbonyl sulfide,
and ozone (Grzywacz 2006, Tétreault 2003).
Perhaps the best way to prevent pollution-related damage to cultural objects is
through developing a strong understanding of museum environments, atmospheric
monitoring, and pollutant mitigation. Such knowledge promotes swift action when
needed and the ability to prevent potential issues. In addition, monitoring alerts
collection managers of these potential issues, such as display case materials that
produce high levels of acetic acid, pollution sorbent media that requires
replacement, or an ineffective HVAC system. The earliest record of collection
Strategies for Pollutant Monitoring in Museum Environments 8
deterioration resulting from environmental conditions was published in 1899 by
Loftus St. George Byne (Byne 1899). He described the visible corrosion of shell in
wooden cabinets, but was not able to make the connection between deterioration
and storage conditions. Environmental monitoring in collections has generated
significant interest within recent decades, producing a number of comprehensive
publications for museum professionals. Originally published in 1978, The Museum
Environment by Garry Thomson is one of the first comprehensive collections of
preventive preservation information (Thomson 1986). It discusses gaseous
pollution as well as the effects of light, humidity, and particulates in cultural
heritage applications. More recent information on museum pollutants is available
through reviews by Brimblecombe and Watt (Brimblecombe 1990, Watt, et al.
2009). Publications by Blades, Hatchfield, Tétreault, and Grzywacz focus on
developing practical pollutant monitoring, mitigation, and control strategies
(Grzywacz 2006, Tétreault 2003, Blades, et al. 2000, Hatchfield 2002). In addition,
multiple recent collaborations between universities, museums, and industry have
produced devices specifically intended for cultural heritage (Dahlin, et al. 2013,
Grøntoft, et al., 2010, Gross, et al. 2017, Kouril, et al. 2013, Thierry, et al. 2013,
Schalm 2014, Odlyha, et al. 2007). At this time, very few commercial products are
available from these studies. Cultural institutions must therefore rely on monitors
intended for industry applications or air samplers that require laboratory analysis.
Many of these techniques can be adapted for museums with careful consideration.
For more information and updates on recent advances in museum environment
monitoring, one can consult websites for the Indoor Air Quality in Museums and
Archives Working Group (http://www.iaq.dk/), the Canadian Conservation
Institute (https://www.canada.ca/en/conservation-institute.html), and the Image
Permanence Institute (https://www.imagepermanenceinstitute.org/).
This review intends to cover general existing knowledge on a few different but
closely related topics:
Gaseous pollutants known to be problematic for heritage collections and
the ways in which they react with cultural materials
Published guidelines for material selection in cultural heritage to reduce
harmful pollutants
Available tools for air quality monitoring in cultural heritage environments
The Background section of this report begins with general information on the most
important pollutants found in museum environments. This includes both outdoor
pollutants that can filter indoors as well as pollutants that are generated by indoor
materials. The pollutants discussed are considered the most important for cultural
heritage collections because they have documented negative effects on objects.
Following this is a collection of existing guidelines on selecting appropriate
materials for storage and display to reduce harmful pollutants in collections.
Finally, available tools for pollutant monitoring are discussed. These include air
sampling techniques, dosimeters, and sensors. The capabilities of each technique
Strategies for Pollutant Monitoring in Museum Environments 9
are discussed to provide the reader with a general overview of existing options and
recent research. Methods to reduce pollutants in collections are briefly discussed,
but more in-depth information on this topic will be available in a forthcoming
publication from RAÄ. Following this general overview, the pollution monitoring
project at Nationalmuseum is presented. For this project, passive air quality
samplers were purchased from the Swedish Environmental Research Institute
(IVL), Gradko International, and Purafil. These samplers collected pollutants over
a period of time and were then mailed back to their respective companies for
laboratory analysis. The results from analyses are presented along with some
suggestions for future monitoring practices in the museum. Information compiled
within this report will provide cultural heritage professionals with a knowledge
base to initiate their own pollutant monitoring practices.
Strategies for Pollutant Monitoring in Museum Environments 10
Background
Gaseous pollutants in the museum environment
To effectively reduce and control pollutants, it is important to understand their
potential sources and the effects that they have on cultural materials. Sources
include outdoor atmospheric pollution, indoor building and construction materials,
display and storage materials, staff and visitors, and other collection objects. While
there are no straightforward answers for acceptable levels of gaseous pollutants in
collections, this review will present some general guidelines found in the
conservation literature. These guidelines are not strict because achievable pollutant
levels are highly dependent on collection materials and the practical capabilities of
the institution. The following section describes the major pollutants of concern to
cultural heritage environments. Table I under Guidelines for pollution levels
condenses the information into a comparative chart. Human health concerns related
to pollution are not covered in the following report. In addition, the focus of this
review is intended for indoor heritage. While the effects of pollution and control
strategies for outdoor heritage are briefly discussed, further sources should be
considered for complete comprehension.
Sulfur dioxide (SO2)
A primary outdoor pollutant, sulfur dioxide is partly the result of fossil fuel
combustion. All of these fuels, including coal, petroleum, oil, and natural gas,
contain sulfur, which combines with oxygen during combustion to form sulfur
dioxide. Furthermore, sulfur dioxide easily oxidizes and combines with water to
form sulfuric acid, H2SO4, found in acid rain (Thomson 1986). In addition to
combustion, sulfur dioxide is produced through the pulp and paper industry,
vulcanized rubber, sulfur-containing geological specimens, and proteinaceous
materials inside enclosures (Tétreault 2003). Sulfur dioxide production also stems
largely from natural biological activity. Combustion-based sulfur dioxide is usually
concentrated in urban, industrial areas, which are often the sites of numerous
museums and historic monuments. Fortunately, outdoor sulfur dioxide
concentrations have significantly decreased in parts of the United States and
Europe since the 1970s due to air pollution regulations. Cultural materials affected
by sulfur dioxide include calcium carbonate (limestone, marble, frescoes,
sandstone), cellulose materials (paper, cotton, linen), proteinaceous materials (silk,
leather, parchment, wool), colorants, synthetic polymers (such as nylon), and
metals. Sulfuric acid dissolves calcium carbonate-based objects such as outdoor
sculpture and building facades (Steiger 2016). Cellulose materials such as paper
become yellowed and brittle in the presence of sulfuric acid (Begin, et al. 1999).
This issue worsens in the presence of ultraviolet light (Hon and Shiraishi 2000).
Proteinaceous materials become powdery when exposed to sulfuric acid, causing a
form of deterioration known as “red rot” in vegetable-tanned leather (Kite and
Thomson 2006). Iron is particularly affected by sulfuric acid, commonly corroding
in urban atmospheres with higher relative humidity (Thomson 1986). In addition,
Strategies for Pollutant Monitoring in Museum Environments 11
outdoor bronzes and other copper-based metals are affected by atmospheric
sulfuric acid (Scott 2002).
Ozone (O3)
Ozone production stems from many sources, both indoor and outdoor. Within the
stratosphere, ozone is the result of natural chemical reactions between short-
wavelength (less than 300 nm) ultraviolet radiation and oxygen. Natural ozone is
also found at ground level as the result of mixing between atmospheric layers.
Man-made ozone is produced through interactions between car exhaust and
sunlight, known as photochemical smog, and through electronic arcing, electronic
air cleaners, electrostatic filtering systems, laser printers, photocopy machines, and
ultraviolet light sources. Known as a powerful oxidant, ozone reacts with organic
material in heritage collections causing brittleness, cracking, and fading. For
example, ozone has shown to fade colorants (Whitmore, Cass and Druzik 1987,
Grosjean, Grosjean and Williams 1994 ); cause embrittlement of rubber and
cellulosic materials (Lee, Holland and Falla 1996, Jaffe 1967, Katai and Schuerch
1966); and discolor photographic prints and ink-jet prints (Lavédrine 2003). In
addition, ozone can oxidize aldehyde organic compounds into carboxylic acids like
acetic acid and formic acid (discussed under Volatile organic compounds), and
increase the corrosion rate of copper (Graedel, Franey and Kammlott 1984).
Nitrogen oxides (NOx)
The most important nitrogen oxides in heritage studies are nitrogen dioxide (NO2)
and nitrous oxide (NO), which are also primary causes of photochemical smog.
Both compounds are produced by fuel combustion, agricultural fertilizers, gas
heaters, and lightning. In addition, nitrogen dioxide emits from deteriorating
cellulose nitrate in indoor conditions (Health and Safety Executive 2013). Nitrogen
dioxide is produced from all combustion processes but nitrous oxide is primarily
found in automobile combustion exhaust. The atmospheric concentrations of
nitrogen oxides steadily increased from the start of the industrial revolution up until
the 1980s, when it began decreasing in the United States and Europe thanks to air
pollution regulations (Tétreault 2003). Similar to sulfur dioxide, nitrogen dioxide
reacts with water to form nitric acid, a strong acid and oxidizing agent that reacts
with metals, cellulose, leather, and calcium carbonate stone. Some examples of
collection issues with nitrogen oxides include fading of artists’ colorants on paper,
silk, and textiles (Grosjean, Grosjean and Williams 1994, Whitmore and Cass
1989); and the acidification of cellulose paper (Begin, et al. 1999).
Reduced sulfur gases
Both an outdoor and indoor pollutant, hydrogen sulfide (H2S) is present in low
concentrations in the atmosphere, but plays a role in the deterioration of silver,
copper, bronze, and lead white pigments to produce visible corrosion over time.
These degradation products are found on metal objects (Sease, et al. 1997), silver-
based photographs (Lavédrine 2003), paper (Smith, Derbyshire and Clark 2002),
and paintings (Carlyle and Townsend 1990). Hydrogen sulfide is produced by fuel
and coal combustion, volcanoes, petroleum and pulp processes, humans, marshes,
Strategies for Pollutant Monitoring in Museum Environments 12
oceans, and vehicle exhaust. It is highly poisonous to humans in elevated
concentrations, but has the distinct smell of rotten eggs that can be detected at the
parts per billion (ppb) level. Objects that are highly sensitive to hydrogen sulfide
gas, such as silver objects or photographs, are known to show signs of deterioration
when exposed to parts per trillion (ppt) gas concentrations (Watts 2000). Indoors,
hydrogen sulfide is produced by vulcanized rubber materials, felts and furs,
adhesives made from animal hide, feathers, composite boards, minerals containing
pyrite, and some objects excavated from waterlogged sites. Other reduced sulfur
gases include carbon disulfide (CS2) and carbonyl sulfide (COS), which are mainly
produced in nature. Wool, for example, tends to produce carbonyl sulfide,
particularly when exposed to ultraviolet light. Studies suggest that if wool and
materials sensitive to sulfide gases (such as silver) must be exhibited together, light
exposure should be reduced (Brimblecombe, Shooter and Kaur 1992).
Volatile organic compounds
Volatile organic compounds (VOCs) are molecules containing hydrogen and
carbon with a high vapor pressure at room temperature, causing them to exist in a
gaseous state at typical ambient conditions. They have a variety of sources,
including paints, coatings, fossil fuels, tobacco products, personal care products,
construction materials, and cleaning agents. Many VOCs are known to be
hazardous to human health, thus VOCs are commonly measured to indicate indoor
air quality. The major VOCs that are a concern for collections are aldehydes in the
form of formaldehyde (methanol) and acetaldehyde (ethanol), and carboxylic acids
in the form of acetic acid (ethanoic acid) and formic acid (methanoic acid).
Formaldehyde and acetaldehyde are problematic for objects primarily because they
can oxidize to create formic acid and acetic acid, respectively. This oxidation
process requires the presence of strong oxidants such as ozone in the atmosphere.
Some studies have suggested that formaldehyde oxidizes to formic acid on the
surface of objects (Tétreault 2003).
Acetic acid is known to affect metals (particularly lead), calcareous materials
(shell, limestone, calcium-rich fossils), soda-rich glass, and cellulose. Examples of
deterioration due to acetic acid include the corrosion of lead-rich organ pipes in
churches (Niklasson, et al. 2008), discoloration of pigments (Oikada, et al. 2005),
and depolymerization of paper (Dupont and Tetreault 2000). Through reactions
with organic acids, lead is converted into lead acetate or lead formate. Bronze and
zinc are also affected by organic acids but to a lesser extent (Tennent and Baird
1992). Ceramics, fossils, and calcareous materials develop calclacite or
thecotrichite deposits, and shells are known to form calcium acetate hydrate and
calcium acetate hemihydrate when exposed to acetic acid (Gibson and Watt 2010,
Gibson, Cooksey, et al. 2005). Known more colloquially as vinegar, acetic acid is
off-gassed by wood products, some silicone sealants, deteriorating cellulose
acetate, paints, linoleum, and cleaning solutions. Furthermore, acetaldehyde is
produced by wood products and some polyvinyl acetate adhesives. Gibson and
Watt studied volatile acetic acid from a number of wood species, identifying
afromosia, oak, obechie, beech, mahogany, larch or red pine as the most significant
Strategies for Pollutant Monitoring in Museum Environments 13
acetic acid producers. In addition, acetic acid production from wood generally
increased with increases in relative humidity and temperature (Gibson and Watt
2010, Niklasson, et al. 2008).
Oil-based paints and wood products tend to emit formic acid, readily reacting with
lead materials to produce lead formate corrosion products. Additionally, glass
objects develop sodium formate deposits, and shell collections have formed
calcium acetate formate hydrate salts as the result of exposure to formic acid
(Gibson and Watt 2010). Formaldehyde has a number of sources including carpet,
paints, gas ovens and burners, tobacco smoke, vehicle exhaust, ozone-generating
air purifiers, and some adhesives (Tétreault 2003). While formaldehyde is
primarily harmful to cultural heritage objects because it can oxidize to formic acid,
its presence in museum environments must also be considered for human health
reasons.
Other pollutants
Oxygen causes material deterioration through oxidation, causing brittleness,
cracking, yellowing, and fading. Hydrogen chloride gas is known to cause metal
corrosion, particularly of silver and copper (Graedel 1992, Leygraf, et al. 2016).
Ammonia (NH3) is emitted by cleaning products, some silicone sealants, concrete,
and some paints. It can react with metals to form an ammonium salt and cause
efflorescence on cellulose nitrate. In addition, it can form white surface deposits on
objects if combined with a sulfate or nitrate (Tétreault 2003). Peroxides from smog,
rubber tiles, wood products, and oil-based paints, are known to discolor
photographic prints and colorants (Reilly, et al. 1988). Particles are a source of
deterioration in cultural heritage, but are not discussed further in this document.
They may abrade or discolor surfaces, have the potential to accelerate corrosion
processes, and can instigate insect or mold damage.
Beyond the pollutants previously discussed, there are examples of deterioration
issues in museums caused by compounds that were previously unknown as harmful
pollutants. These examples show some of the inherent challenges in measuring for
pollutants and the continually evolving nature of air quality monitoring. Two recent
investigations studied the formation of white crystals on display case interiors and
collection objects (Newman, et al. 2015, Stanek, et al. 2016). In both studies, the
probable source was thought to be an adhesive used in display case construction.
While the commercial adhesive products were different for the two separate
studies, both contained piperidinol-based compounds. Similar compounds were
discovered on the crystalline deposits of the display case and collection objects.
Such corrosion was not detected through previous material emission tests and is not
a compound that is typically screened for during air quality monitoring practices.
Due to these studies, museums now know that materials containing piperidinol-
based compounds should be avoided, but such information was not part of the air
quality monitoring conversation until recently. Especially with the use of new,
ever-changing construction and decoration materials in museums, it is possible that
the number of such examples will continue to grow.
Strategies for Pollutant Monitoring in Museum Environments 14
Guidelines for pollution levels
Material degradation is a complex function, dependent not only on volatile outdoor
and indoor pollutants but also on temperature, relative humidity, light exposure,
particulate matter, object composition, conservation and storage history of an
object, and the synergistic relationships between all of these variables. It is there-
fore difficult to establish environmental standards in cultural heritage monitoring.
Nevertheless, some general guidelines exist. Table I provides a condensed
overview of the major pollutants of concern for cultural heritage collections and
concentration recommendations from the literature. The list is not exhaustive but
rather provides a general overview. More in-depth information is found in the
above section on pollutants. The recommendations discussed are acceptable and
generally obtainable levels at which pollutants can be maintained to prevent
collection damage. While ideally it would be best to have no pollutants in contact
with a collection, this is not feasible. The numbers are therefore derived from
practical considerations for cultural heritage institutions.
Table I: General information about most common pollutants of concern to cultural heritage
environments, their sources, effects on objects, and some concentration recommendations from the
literature.
Pollutant Common sources Effects to cultural
heritage Recommendations (µg/m3)
Sulfur dioxide
(SO2)
Fossil fuel
combustion, pulp
and paper
production,
biological activity,
fuels for cooking
and heating,
vulcanized rubber
Metal corrosion,
dye fading, paper
and textile
embrittlement,
photograph
deterioration
, leather
“red-rot”, pigment
darkening, calcium
carbonate
deterioration
a
of Standards 1983)
Museum interiorsa: < 10 (Thomson
1986)
Libraries, Archives and Museums: 2.7
(NAFA 2004)
Sensitive materialsa: < 0.1 1.1
(Grzywacz 2006)
< 0.2 (Bgvad Kejser, et al. 2012)
Ozone (O3)
Smog,
photocopiers, laser
printers,
electrostatic
particle filters
Rubber
embrittlement, dye
and pigment fading,
photograph
deterioration, book
deterioration, textile
and cellulose
embrittlement, ink-
jet print fading
of Standards 1983)
Museum interiorsa: 0 - 2 (Thomson
1986)
Libraries, Archives and Museums: 4
(NAFA 2004)
Sensitive materialsa: < 0.1 (Grzywacz
2006)
< 1 (Bøgvad Kejser, et al. 2012)
Strategies for Pollutant Monitoring in Museum Environments 15
Nitrogen
dioxide (NO2)
Biological
processes, fossil
fuel combustion,
fuels for cooking
and heating,
cellulose nitrate
decomposition,
tobacco smoke,
photocopiers
Textile dye fading,
textile
embrittlement, ink
and pigment,
photographic film
deterioration
(National Bureau of Standards 1983)
Museum interiorsa: < 10
(Thomson 1986)
Libraries, Archives and Museums: 5
(NAFA 2004)
Sensitive materialsa: < 0.1 5
(Grzywacz 2006)
< 0.1 (Bøgvad Kejser, et al. 2012)
Hydrogen
sulfide (H2S)
Fuel combustion,
wool, silk, felt,
vulcanized rubber,
waterlogged
archaeological
organic materials,
biological
processes, pyrite
collections
Silver and copper
corrosion,
photograph ”silver
mirroring” and redox
spots, leather ”red-
rot”, lead pigment
darkening, stone
deterioration
Sensitive materialsa: < 0.01
(Grzywacz 2006)
Collections in generala: < 0.1
(Grzywacz 2006)
Acetic acid
(CH3COOH)
Wood products,
biological
processes,
laminated
materials, paints,
adhesives,
sealants, cellulose
acetate
decomposition
Metal corrosion (Pb,
Zn), deterioration of
calcareous materials
(shell, fossils,
limestone), cellulose
embrittlement,
enamel and glass
deterioration
Sensitive materialsa: < 12
(Grzywacz 2006)
Collections in generala: 100 - 697
(Grzywacz 2006)
< 12 (Bøgvad Kejser, et al. 2012)
Formic acid
(CH2O2)
Formaldehyde
oxidation, drying
oil paint, wood
products,
adhesives,
sealants
Metal corrosion (Pb,
Zn, bronze),
deterioration of
calcareous materials
(shell, fossils,
limestone), cellulose
embrittlement
Sensitive materialsa: < 9.6
(Grzywacz 2006)
Collections in generala: 9.6 - 38
(Grzywacz 2006)
< 6 µg/m3 (Bøgvad Kejser, et al. 2012)
Formaldehyde
(CH2O)
Wood products,
resins, natural
history specimens,
fiberglass,
photocopiers,
textiles, PVC
carpeting,
laminates
Protein
embrittlement
(leather, parchment,
animal hides), dye
fading, pigment
deterioration, textile
deterioration
(NAFA 2004)
Sensitive materialsa: < 0.1 - 6
(Grzywacz 2006)
Collections in generala: 13 - 25
(Grzywacz 2006)
< 6 (Bøgvad Kejser, et al. 2012)
Acetaldehyde
(CH3CHO)
Textile industry,
wood composites
Oxidizes to acetic
acid in presence of
strong oxidants
Sensitive materialsa: < 1.8 - 37
(Grzywacz 2006)
a = original units given in parts per billion (ppb) and were converted to µg/m3 under the
assumption of STP (standard temperature and pressure) conditions.
Recommendations for achievable pollutant concentrations are based on a number
of factors. For example, the concentrations set by the Royal Library in Denmark
are tailored for their own collection based on the needs of the institution. They
Strategies for Pollutant Monitoring in Museum Environments 16
were developed from professional consultations and from documents such as the
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning
Engineers) Handbook chapter on Museums, Galleries, Archives, and Libraries
(ASHRAE 2015). Recommendations from Grzywacz are dependent more on
literature studies of pollutants in museum environments. For example, materials
sensitive to hydrogen sulfide require environments with very low hydrogen sulfide
concentrations. This is based on the knowledge that silver tarnishes easily when
exposed to very low concentrations (Watts 2000). Other recommendations, such as
that from the National Air Filtration Association (NAFA), were created by air
filtration engineers that primarily focus on outdoor pollutants such as sulfur
dioxide, nitrogen dioxide, and ozone. These recommendations are based on the
capabilities of functional HVAC systems as well as the needs for collections and
visitor comfort.
The recommendation data in Table I is presented in µg/m3, known as gravimetric
units. While it is common to express gas concentrations in this way or by using
mg/m3, volumetric units such as parts per billion (ppb) and parts per million (ppm)
are also commonly used. Volumetric units are dependent on pressure and
temperature, while gravimetric units are not. It is possible to convert between the
two types of units if temperature and pressure are known. Making the assumption
that measurements occur at standard temperature and pressure (STP, where T = 20
°C and P = 1 atmosphere), the following equation for conversion can be used:
Gravimetric units = (x)(Volumetric units) (Eq. 1)
where x is equal to the values given in Table II for some of the most important
airborne pollutants for cultural heritage environments (Grzywacz, 2006).
Table II: Values of x for equation 1 under standard temperature and pressure. The values are used to
convert ppb to µg/m3 (and vice versa) or to convert ppm to mg/m3 (or vice versa) (Grzywacz, 2006).
Compound x value
Acetic acid 2.49
Acetaldehyde 1.83
Formic acid 1.91
Formaldehyde 1.25
Sulfur dioxide 2.66
Hydrogen sulfide 1.41
Nitrogen dioxide 1.91
Nitric oxide 1.25
Ozone 1.99
Converting volumetric units (ppb, ppm) to gravimetric (µg/m3, mg/m3) requires
multiplying by the given value for x, and converting gravimetric units to
Strategies for Pollutant Monitoring in Museum Environments 17
volumetric requires dividing by the given value for x. For example, to convert a
sulfur dioxide (SO2) concentration of 5 ppb at STP, one must multiply it by 2.66
(given in Table II) to receive a value of 13.3 µg/m3. Conversely, a value of 13.3
µg/m3 is divided by 2.66 to receive the volumetric units in ppb.
In addition to the recommendations given in Table I, Jean Tétreault at the Canadian
Conservation Institute developed guidelines for ways to theoretically determine
relationships between pollution exposure and material deterioration. Such
relationships are known as the no and lowest observed adverse effect levels
(NOAEL and LOAEL, respectively). A NOAEL measurement indicates the highest
level of a specific pollutant that does not produce an observable effect on a
characteristic of an object under certain environmental conditions. LOAEL is
therefore the concentration of a specific pollutant that produces the first signs of an
adverse effect (Tétreault 2003). This information is summarized in Tétreault’s
book Airborne Pollutants in Museums, Galleries and Archives, and can be used as
a means to initiate a collection risk assessment before beginning a pollution
monitoring program.
Indoor vs. outdoor pollutants
One of the most important factors in determining an object’s wellbeing is its
surrounding environment. In museums, objects are housed in either larger
environments such as galleries or storage areas (occasionally called macro-
environments), or smaller spaces such as display cases or storage containers
(microenvironments). The pollutant levels found in these environments depend on
a number of factors, including the outdoor pollution concentrations, type of
building ventilation, materials inside the environment, air exchange rate, tempera-
ture, humidity, and surface adsorption. For example, some studies have found high
acetic acid concentrations inside museum storage containers and display cases
(Grzywacz and Tennent 1994, Thickett, Bradley and Lee 1998, Schieweck and
Salthammer 2011). This could be due to the materials used to construct the
container (i.e. wood or sealants) as well as low ventilation. Additionally, low
pollution concentrations measured in an environment could be due to proper
pollutant filtration or blocking, but could also be due to pollutant adsorption by
museum surfaces and objects (Rhyl-Svendsen, et al. 2003). The latter situation may
not be ideal for collection objects. In general, outdoor pollutants are often found in
larger spaces containing windows and doors to the outside, while indoor pollutants
are more common in smaller, more stagnant spaces (Rhyl-Svedsen 2007).
A very general but useful measurement for air quality is the indoor/outdoor (I/O)
ratio (Weschler, Shields and Naik 1989, Grzywacz 2006). For galleries and storage
rooms, the I/O ratio is useful for determining if outdoor pollutants are filtrating into
the building. It can also indicate if there are materials inside the building that are
strongly producing harmful pollutants. The I/O ratio is calculated by dividing the
averaged indoor pollutant concentrations by the averaged outdoor air quality
measurements for the same period of time. Outdoor air quality is often available
through local regulation agencies. For the case study with Nationalmuseum,
Strategies for Pollutant Monitoring in Museum Environments 18
outdoor air quality data from Stockholms Luft- och Bulleranalys (SLB Analys) was
used. In general, a ratio greater than 1 indicates that the building is a noticeable
source of pollution, whereas a ratio less than 1 indicates that the building is
filtering outdoor pollutants. This concept can also be applied to microenviron-
ments, in which the “indoor” numerator is the pollutant concentration within a
given microenvironment, while the “outdoor” denominator is the pollutant
concentration in the surrounding room.
The I/O ratio is a highly simplified air quality measurement, and must be
interpreted with consideration for the complex nature of atmospheric gases. For
example, the MASTER project, which investigated relationships between indoor
and outdoor levels of nitrogen dioxide, explained that concentrations for indoor
levels of nitrogen dioxide can be higher than concentrations for outdoor levels,
even when indoor sources do not emit NO2. This is due to reactions between ozone
and nitric oxide (NO) in indoor environments, simultaneously decreasing the
indoor ozone concentration while increasing the indoor nitrogen dioxide
concentration (Grøntoft, Dahlin, et al. 2010). In addition, highly reactive pollutants
such as ozone are reduced indoors through interactions with surfaces. Other, more
complex I/O ratio models exist that use parameters such as air exchange rate and
pollutant deposition velocities onto a surface (Weschler, Shields and Naik 1989,
Rhyl-Svedsen 2007). For example, the steady-state I/O ratio, proposed by
Weschler et al. is given below:
=
+
Ci = indoor concentration of pollutant (ppb or µg/m3)
Co = outdoor concentration of pollutant (ppb or µg/m3)
n = air exchange rate (1/h)
vd = deposition velocity (m/h)
A = surface area of room (m2)
V = room volume (m3)
This model works well for outdoor pollutants such as ozone, sulfur dioxide, and
nitrogen dioxide. It was used as the basis for a study on modeling pollutants found
in museum environments (Blades, Kruppa, et al. 2004). Deposition velocity is a
property of a particular pollutant that is dependent on its interactions with surface
materials. It provides an idea of how readily the pollutant will react with the
surface material. Air exchange rate of a room or enclosure can be experimentally
measured using tracer gases (for naturally and mechanically ventialted buildings)
and pressure tests (for naturally ventilated rooms or constructions). Blades states
that a typical air exchange rate for a tightly-sealed room is around 0.1 exchange/
hour, and for crowded public areas is approximately 10 exchanges/hour. Houses
with closed windows tend to have rates between 0.5 and 1 exchange/hour (Blades,
Oreszczyn, et al. 2000).
(Eq. 2)
Strategies for Pollutant Monitoring in Museum Environments 19
Selecting materials for storage and display
To create a safe environment for cultural heritage collections, one of the major
preventive considerations should be appropriate material selection. Such materials
are used to create display cases, storage containers, transportation enclosures, and
general indoor spaces. Many materials produce some form of gaseous emission that
will contribute to the museum air quality. It is therefore important to understand
what these emissions are and if they will harm cultural heritage objects. For
example, lead or calcareous museum objects should not be stored in wood
enclosures because wood is known to produce acetic acid emissions. The process
of selecting appropriate materials for cultural heritage environments involves many
variables and considerations. New materials for storage and display are constantly
being produced but typically are not tested for pollutants that are of concern to
museums. It is therefore difficult to state exactly which materials should be
avoided. Nevertheless, a number of resources exist that can aid the decision-
making process. General overviews of appropriate and inappropriate classes of
materials for cultural heritage are available through the following literature:
Tétreault, Jean. 1993. Guidelines for Selecting Materials for Exhibit, Storage and
Transportation. Canadian Conservation Institute: Ottawa, Canada.
Tétreault, Jean. 1999. Coatings for Display and Storage in Museums. Canadian
Conservation Institute: Ottawa, Canada.
http://www.publications.gc.ca/site/eng/9.810462/publication.html.
Pasiuk, Janet. 2004. Conserve O Gram: Safe Plastics and Fabrics for Exhibit and
Storage. National Park Service: Washington, D.C.
https://www.nps.gov/museum/publications/conserveogram/18-02.pdf.
Museums Galleries Scotland. Introduction to Storage and Display Materials.
https://www.museumsgalleriesscotland.org.uk/advice/collections/introduction-to-
storage-and-display-materials/.
Wiltshire County Council Conservation Service. 2006. Signposts Factsheet 2:
Materials for Storage and Display. South West Museums, Libraries and Archives
Council, Salisbury, Wiltshire. https://www.swfed.org.uk/wp-
content/uploads/2013/02/signposts_materials.pdf.
Riksantikvarieämbetet (Swedish National Heritage Board). 2017. Vårda väl:
Material för utställning, förvaring och packning: Vanliga material.
https://www.raa.se/ vardaval.
Riksantikvarieämbetet (Swedish National Heritage Board). 2017. Vårda väl:
Material för utställning, förvaring och packning: Allmänna utgångspunkter.
https://www.raa.se/ vardaval.
In addition, a number of online databases and lists describe specific products and
materials that have been tested and used in cultural heritage applications. Such
databases and lists include:
Strategies for Pollutant Monitoring in Museum Environments 20
Oddy Tests: Materials Database through the American Institute for Conservation
Wiki page. http://www.conservation-wiki.com/wiki/Oddy_Tests:_Materials_Databases.
Database of Materials Test Results (Oddy Test Results) by the British Museum
https://www.britishmuseum.org/research/publications/research_publications_series
/2004/selection_of_materials.aspx.
CAMEO: Conservation & Art Materials Encyclopedia Online by the Museum of
Fine Arts Boston. http://cameo.mfa.org/wiki/Category:Materials_database.
Preserv’Art database by the Centre de Conservation Québec.
http://preservart.ccq.gouv.qc.ca/index.aspx.
STASHc (Storage Techniques for Art, Science & History Collections) by the
Foundation of the American Institute for Conservation.
http://stashc.com/resources/materials-and-suppliers/.
Photographic Activity Test results by the National Archives of Australia.
http://naa.gov.au/information-management/managing-information-and-
records/preserving/physical-records-pres/pat.aspx.
Tools for pollutant monitoring
A number of air sampling devices exist for collecting and monitoring pollutants in
the museum environment, whether these pollutants derive from indoor or outdoor
sources. Such tools are used to measure the air quality of a given space and can
collect a range of compounds. No single device can measure for all airborne
pollutants, which means that museum professionals must choose which compounds
they wish to measure. A guide to the most important pollutants for cultural heritage
preservation is found in the section Gaseous pollutants in the museum environment.
Additionally, an air quality monitoring project may involve multiple different air
sampling devices that are deployed simultaneously. Many of these tools are small
enough to be used inside display cases and storage containers.
Unfortunately, at this time there are very few commercially available air
monitoring devices tailored specifically for cultural heritage. Museums must
therefore adapt existing tools to fit their own needs. This is simple but there are
some limitations to consider. For one, some devices may not be sensitive enough to
detect low pollutant concentrations. As an example, silver is susceptible to
corrosion by hydrogen sulfide at ppt concentrations, which may be too low for
many devices to detect. Measurements in museums often occur in enclosed,
stagnant spaces like display cases. This can be a challenge for many passive and
active sampling techniques (discussed later in this segment) due to the lack of
airflow and due to the need to maintain an enclosed envelope during measure-
ments. Therefore, an important aspect of any pollutant monitoring project is
communication. By communicating the needs of your institution to companies that
provide air quality monitoring devices or services, one can understand the
possibilities and limitations of the pollutant monitoring process.
Strategies for Pollutant Monitoring in Museum Environments 21
This review will discuss some existing air quality monitoring devices that can be
used in cultural heritage environments. The list of tools mentioned are by no means
exhaustive. For museum purposes, the basic functions of each device can be
described using four primary questions:
Is the device an air sampler or a dosimeter?
Does the device collect passively or actively?
Is the device “direct-read” or does it require laboratory analysis?
Does the device provide qualitative or quantitative results?
Air samplers produce data on the composition of the air while dosimeters provide
synergistic information about reactions between a material and its environment.
Active devices use forced air to reduce the collection time while passive collect by
natural air diffusion. Direct-read tools are easily interpreted on site while
laboratory analyzed tools require analytical techniques to retrieve information.
Finally, qualitative results identify volatile compounds or corrosion products while
quantitative results give specific concentrations or other numerical data. All of the
above terms will be discussed in further detail. One can usually answer all four
questions for a single device. For example, the devices used for the case study at
Nationalmuseum (created by the Swedish Environmental Research Institute, IVL)
are air samplers that collect passively, require laboratory analysis, and provide
quantitative results. If a question cannot be answered from the device description, it
may be necessary to contact the manufacturer for further information. This review
will discuss basic device functions so cultural heritage institutions can determine
which of these qualities fit their needs. Other practical considerations, including
general cost, time, and ease of use will be discussed as well.
Appendices A and B provide information about some existing commercial devices
that can be applied to cultural heritage air monitoring practices. Appendix A
presents a flow chart indicating the four qualities of different commercial devices
(sampler/dosimeter, passive/active, direct-read/lab analysis, quantitative/qualitative).
It includes information about the general costs of the device categories. Appendix
B is a table describing some available devices, including information about the
types of pollutants they measure, general ease of use, detection limits, and
measurement time.
Air samplers vs. dosimeters
Air samplers
Air samplers are devices that collect chemical compounds from the air and provide
information about these compounds. This collection process can occur through a
number of different methods. For example, samplers may contain porous media
like silica gel or activated charcoal that trap certain molecules. They may also
contain a reagent that chemically reacts with specific compounds in the air. An air
sampler can be manufactured to collect a range of compounds (VOCs, for
example) or to collect a single compound (i.e. ozone). Depending on the type of
device, the information provided can include the names of the collected compounds
Strategies for Pollutant Monitoring in Museum Environments 22
as well as their concentrations in the air. Air samplers can be active or passive,
direct-read or laboratory analyzed, and qualitative or quantitative. These categories
are explained in detail in further sections below. When setting up an air quality
monitoring project, each space typically receives one of each type of sampler.
Other practical information about air samplers is provided in Pollution monitoring
practices in museums.
While samplers provide useful and specific information about the composition of
air, this information is only valuable if the end-users are able to use it. The museum
environment is complex, containing a wide variety of materials with different
reactions to pollutants at varying concentrations. As mentioned previously in
Guidelines for pollution levels, it is therefore difficult to set guidelines for pollutant
levels in cultural heritage contexts. Such guidelines are further complicated by
other environmental factors such as light, humidity, temperature, and prior storage
conditions. It is possible for an institution or collection care manager to decide
appropriate levels for their collection and use these concentrations as a reference
during air quality monitoring projects. Air samplers are useful for such situations.
However, it is also possible that the information provided by an air sampler will be
lost on someone that does not have a strong understanding of the collection needs
or of the collection environment. Additionally, many commercially available air
samplers are intended for human safety and may not have low enough detection
limits for cultural heritage applications. It may be possible to expose such samplers
for a longer period of time to increase the sensitivity. Detection levels and the
potential for increased sensitivity must be discussed with the sampler manufacturer
before an air monitoring project.
Dosimeters
Unlike air samplers, dosimeters do not directly provide information about specific
compounds and their concentrations in the air. Rather, they are cumulative
indicators of how certain materials react with their surrounding environment. For
example, a dosimeter can be composed of a simple lead coupon and will act as a
long-term passive monitor. As lead is highly sensitive to acetic acid and formic
acid, the accumulation of lead corrosion products can indicate that care should be
taken to prevent collection damage. If the lead coupon is paired with a device like a
quartz crystal microbalance, the dosimeter can provide a preventive warning when
the lead corrosion products reach a certain mass. Dosimeters therefore react to all
synergistic components of their surrounding environment, including pollutants,
temperature, humidity, and light. They can also be used for long periods of time,
acting more like continual monitors rather than one-off measurement devices.
However, the deterioration properties of the dosimeter may not be representative of
the collection material properties. Additionally, due to their cumulative nature,
dosimeters cannot be reverted to their original state. Dosimeters are only passive in
nature, but they can be direct-read or laboratory analyzed, and qualitative or
quantitative. Quantitative analysis of a single environmental parameter, such as
acetic acid concentration, may be possible but is difficult and requires complex
techniques (Agbota, Young and Strlič 2013).
Strategies for Pollutant Monitoring in Museum Environments 23
A number of institutions have investigated dosimeters as environmental indicators
for cultural heritage applications (Grøntoft, Dahlin, et al. 2010, Odlyha,
Theodorakopoulos, et al. 2007, Odlyha, Slater, et al. 2018). At this time, the
products are not commercially available. Some of these dosimeters are available as
prototypes by the developers, such as the product from the MEMORI Project
(Dahlin, et al. 2013). Examples of dosimeters developed and used for cultural
heritage studies include piezoelectric quartz crystal microbalance dosimeters
(QCM), early warning dosimeters for organic materials (EWO), tempera-painted
dosimeters, and glass slide dosimeters (Agbota, Young and Strlič 2013). Quartz
crystal microbalance dosimeters, such as the commercially available Purafil
OnGuard technology, are based on sensors that change their oscillation frequency
with a change in mass. Thin layers of corrosion buildup on a surface cause an
increase in sensor mass, thus producing a readable output. In the cultural heritage
sector, QCM prototypes focus on specific materials such as organic artist coatings
(from the MIMIC project) and lead organ pipes (from the SENSORGAN project)
(Odlyha, Theodorakopoulos, et al. 2007). Additionally, a more generic and
synergistic QCM dosimeter was developed for the Accessible Heritage Project at
University College London. It assessed pollutants, temperature, and humidity
conditions and was tested at historic sites in the UK and West Africa (Agbota,
Mitchell, et al. 2014, Agbota, Accessible Heritage n.d.). An EWO dosimeter was
developed through the MASTER and PROPAINT projects, and is composed of a
synthetic polymer sensitive to temperature, light, humidity, nitrogen dioxide, and
ozone (Grøntoft, Dahlin, et al. 2010, López-Aparicio, et al.. 2010, Lopez-Aparicio,
Grøntoft and Dahlin 2010). It is intended as a tool to assess the indoor air quality of
cultural heritage institutions. Spaces studied included both entire rooms and
smaller enclosures such as painting enclosures. Finally, a glass slide dosimeter
developed for cultural heritage reacts to relative humidity and acidic pollutants. It
measures glass corrosion using FTIR spectroscopy in reflectance mode (Leissner
2016).
The aforementioned dosimeters are not yet commercially available and do not exist
as a single, compact tool. Additionally, interpretation of the dosimeters requires
tools such as microscopes or spectrometers (Agbota, Young and Strlič 2013). The
MEMORI project focused intently on creating a commercially viable, hand-held
tool for cultural heritage institutions, but the product is still in its prototype phase
(MEMORI Project contributors n.d.). Despite the lack of existing commercial
technology for museums, it is possible to use dosimeters intended for industry
applications. For example, the Purafil OnGuard quartz crystal microbalanace has
been used in museums to study air quality. Additionally, the AirCorr monitor
developed by the French Corrosion Institute was used in the MUSECORR project
for a number of cultural heritage locations, including the Mariners’ Museum, the
Kunsthistorisches Museum, and Australian War Memorial (Kouril, et al. 2013,
Prosek, et al. 2013, Prosek, Le Bozec and Thierry 2014, Thierry, et al. 2013). This
monitor is commercially available and uses electrical resistance measurements of
thin metal tracks. These tracks corrode over time and give real-time measurements
of air quality (French Corrosion Institute n.d.).
Strategies for Pollutant Monitoring in Museum Environments 24
Metal coupons can also be used as simple dosimeters, much like the lead coupon
mentioned previously. Other types of coupons used include copper, silver, and
occasionally brass. The corrosion products are assessed visually or through
electrochemical reduction processes. Corrosion on copper indicates the presence of
sulfides, chlorides, nitrogen dioxide, and sulfur dioxide; silver corrosion indicates
hydrogen sulfide and carbonyl sulfide; and lead corrosion indicates carbonyl
pollutants and acid pollutants (Grzywacz 2006). The exposed coupons must be
compared to a protected, non-exposed control coupon. As an example, sets of
silver, copper, and lead coupons were used as passive devices inside display cases
of several French cultural heritage institutions. After collection, the coupons were
electrochemically reduced and corrosion products such as silver chloride and silver
sulfide were identified (Costa and Dubus 2007). Some air filtration companies
manufacture sets of silver and copper coupons, often called corrosion coupons or
reactivity monitoring coupons. After exposure for one to three months, they are
returned to the respective company for electrochemical analysis. The results are
presented in thickness of the identified corrosion product, either in units of
nanometers or ångströms, and are classified using standard ISA-71.04-2013 or ISO
11844-1:2006. The corrosion products and their thicknesses help to infer the
pollutants present and their possible concentrations. These coupons do not require
sensors or electrical equipment and are therefore affordable options for air quality
analysis. Examples of some available devices for this type of analysis are given in
Appendix I and Appendix II.
Passive vs. active devices
Passive devices
Passive devices collect pollutants or react with their environment without help
from forced air. All dosimeters discussed in this report are passive and some air
sampling devices are passive. Such devices are used for a long period of time,
ranging between several hours to several months. Passive air sampling devices in
particular collect volatile compounds via natural diffusion and are usually small
and simple vessels. If quantitative, the results are provided as an average value
from the course of the exposure time. Depending on the device, a passive tool can
produce qualitative or quantitative data, and can be direct-read or laboratory
analyzed. Examples of devices include cylindrical tubes containing an adsorbent or
reagent, a metal coupon, dyed paper strips, or coated fibers.
Despite the fact that passive devices do not used forced air, airflow is still
important, particularly for air sampling tools that work by diffusion. Such diffusion
will not properly occur in spaces with very low air velocities, i.e. areas with air
velocities of less than 7.6 meters/minute at the face of the sampler (Salter n.d.).
Uptake rates by passive air sampling devices are not well explored and may differ
for different compounds (Bohlin, et al. 2014, Newton, et al. 2016). Such uptake
rates are affected by changes in wind (if measuring outdoors), relative humidity,
and temperature. If measuring in an area with very low airflow, such as a display
case with no internal air circulation, the sampling rate of the passive sampler will
be significantly reduced. This will produce results that are lower than the actual
Strategies for Pollutant Monitoring in Museum Environments 25
environmental concentrations. Some companies that provide laboratory analysis of
their devices do account for the low airflow in indoor spaces. It is still necessary to
consult with the manufacturer on whether their devices are appropriate for the
intended application. Conversely, high air velocities and high humidity can inhibit
the air sampler’s ability to adsorb the appropriate compound. These factors must be
considered when performing passive air sampling in all cultural heritage
environments.
Benefits of passive tools include their compact size, ease of use, affordability, and
lack of noise. As they do not require air pumps, passive devices can be placed in
small, enclosed spaces like display cases or storage containers. The lack of a pump
also generally means that passive devices cost less than active devices (discussed
below) and do not require calibration or specialized skills for collection. Their long
exposure time is also beneficial for cultural heritage contexts because as mentioned
previously, it provides a long-term, time-weighted average measurement. This type
of measurement is not as subject to anomalous issues like spikes in compound
concentrations. Long, averaged exposures are more representative of the long-term
museum environment, but such conditions make passive devices more susceptible
to contamination (Ras, Borrull and Marce 2009). Furthermore, as passive devices
must collect for several days or weeks at a time, it may be difficult to place them in
highly visible public spaces such as display cases. Results from passive devices are
not instantaneously obtainable. The planning of passive air quality monitoring
projects must therefore be done with respect to the collection time.
Active devices
Active devices are similar to passive devices, but include the use of air pumps or
forced airflow, decreasing the air collection time to last between several seconds to
a few hours. Air samplers can be adapted for active measurements, while
dosimeters are passive devices. Dosimeters provide data about metal corrosion
rates that happen over real time rather than pollutant concentrations. Air pumps are
not necessary for corrosion rate measurements. The process of active sampling
requires a continuous, known airflow rate into a sampler vessel. Adsorbents are
often used as vessels, but bags and canisters are also common collection media.
Like passive devices, active devices can be direct-read or laboratory analyzed, and
qualitative or quantitative. Compounds are identified and concentrations are
calculated using the same methods as for passive samplers. As the use of forced air
significantly shortens the collection time, the results from an active device provide
more of a snapshot analysis of air quality. This is beneficial if results are needed
rapidly, but such short measurements are more strongly affected by possible
anomalies in air quality. For example, if the HVAC system of a building is not
working properly on the day of measurement, the results from an active device may
show anomalously high levels of outdoor pollutants that may not be representative
of the long-term air quality.
Active sampling techniques are less susceptible to contamination than passive
techniques, but are more likely to suffer from breakthrough issues (Ras, Borrull
Strategies for Pollutant Monitoring in Museum Environments 26
and Marce 2009). Breakthrough occurs when a contaminant saturates the adsorbent
inside the collection tube and filters into a backup layer of adsorbent located in the
back of the tube. Many sorbent tubes contain this secondary backup layer in
addition to the main adsorbent. Breakthrough often occurs as the result of high
concentrations of the target compound or similar compounds. This is more likely to
happen during an active sampling process because of the higher air flow rate (SKC
Limited 2015).
Practically speaking, active sampling processes are less suitable for spaces that
need to remain closed to maintain a microenvironment, such as display cases. By
opening the display case, one disturbs the microenvironment within. An active
device will therefore measure a mix of the display case environment and the
environment of the surrounding room. Passive devices also require opening a
display case, but allow the microenvironment more time to re-equilibrate during
measurement. Active sampling is therefore better suited for measuring other indoor
spaces like galleries and storage rooms. Due to the use of pumps, active air
sampling is generally more costly than passive sampling. Additionally, the
collection process is more complex as the pumps require calibration to calculate the
total air volume collected during sampling. Once the user is comfortable with the
pump technology, active sampling methods can be quite convenient as many air
pumps are programmable to perform scheduled collections at particular times.
While the active sampling process can be complex, it is possible to hire indoor air
quality services or consultants who arrive on location with calibrated pumps and
perform the measurements. Once again, in such cases communication about the
needs and intentions of the institution requesting such services is extremely
important. Many companies that provide passive sampling devices also sell tools
for active sampling. In heritage studies, active sampling processes have been used
to analyze acetic and formic acid in church organ pipes (Niklasson, et al. 2008),
organic acids inside museum display cases (Dremetsika, Siskos and Bakeas 2005),
and VOCs in library archives (Gibson, Ewlad-Ahmed, et al. 2012). Active
sampling of display case interiors has also been performed by incorporating small
tubes inside closed cases that suck air onto coupled sampling devices (Schieweck,
2009).
Direct-read vs. laboratory analyzed devices
Direct-read devices
Direct-read devices are samplers or dosimeters that produce visual information for
the end-user to interpret on site. There is no need to send direct-read devices to a
laboratory for analysis. Such devices can be passive or active, qualitative or
quantitative, depending on the manufacturer. Analysis is often performed by
interpreting color changes. Some of these devices, such as the A-D Strip (explained
below) were developed specifically for cultural heritage applications, although
many have been adapted from industry.
Qualitative direct-read tools are exposed to their surrounding atmosphere without a
barrier to control diffusion. They are useful as screening devices to indicate
Strategies for Pollutant Monitoring in Museum Environments 27
locations that require more in-depth investigations. The A-D Strip is an example of
a qualitative direct-read device. It is dyed paper strip that indicates the presence of
acid gases (acetic acid and formic acid, primarily) through a color change from
blue to green or yellow. Invented to detect acetic acid evolution from cellulose
acetate film and photographic negatives, A-D Strips can also be adapted to monitor
acid pollutants in rooms or enclosed spaces. More information on the strip can be
found through the Image Permanence Institute website:
https://www.imagepermanenceinstitute.org/imaging/ad-strips
Quantitative direct-read systems typically contain reagents that change color in
relation to the concentration of a particular gas. Such systems come in the form of
diffusion tubes, badges, or test sticks. One major issue with colorimetric direct-read
devices is interference from other gases. For example, a device intended to measure
acetic acid is also likely sensitive to other acidic gases, or a device that measures
formaldehyde is also likely sensitive to acetaldehyde. Many direct-read samplers
therefore indicate different classes of compounds. The device manufacturer should
provide information about interference.
It is important to note that many of these devices are designed for health and safety
purposes rather than for cultural materials. They may not be sensitive enough to
detect the low concentrations of gases that negatively react with museum objects. It
is therefore necessary to consult with manufacturers on detection levels. Despite
their limitations, direct-read samplers are certainly useful in museum environ-
ments. For example, a collaborative study between the Smithsonian Institution,
National Gallery of Art, National Museum of Natural history, and building
Dynamics, LLC used A-D strips and Gastec Passive Acetic Acid Dosimeter Tubes
to study acetic acid vapors outdoors, in galleries, and in storage containers (Light,
et al. 2015).
One recent investigation worked to tailor direct-read devices for cultural heritage
applications. A research group at the University of Illinois at Urbana-Champaign
previously developed an optoelectronic nose for biomedical purposes and chose to
adapt the technology for museum environments. The “nose” is an array of
chromogenic indicators that change color according to the presence of particular
volatile compounds and their concentrations. The array is printed on paper and is
disposable. In collaboration with the Getty Conservation Institute and the Walt
Disney Animation Research Library, the research group worked to increase the
sensitivity of the existing technology and design it to indicate the presence of
common museum pollutants. Such a device could help to determine when a
pollutant adsorbent (activated charcoal for example) is no longer filtering and
requires replacement. The device was incorporated into a traveling exhibition of
framed paper works from the Disney library (Cottingham 2016, Suslick n.d.).
Direct-read samplers are very user friendly in the sense that they provide
instantaneous results after the appropriate collection time and are easy to interpret.
As they do not require the use of analytical equipment, they are often more
affordable than laboratory analyzed samplers. Unfortunately, most direct-read
Strategies for Pollutant Monitoring in Museum Environments 28
samplers are not as sensitive as laboratory analyzed samplers. Some direct-read
devices can detect lower concentrations if allowed to collect for longer periods of
time, but it is necessary to discuss this with the manufacturer. Due to their
sensitivity and specificity limitations, direct-read devices are primarily
recommended as basic screening tools for museum environments. It should also be
noted that no single direct-read device can identify all necessary airborne
pollutants. Devices are sensitive to particular compounds or classes of compounds.
When designing an air quality monitoring study, it is often the case that several
different devices are needed depending on the pollutants of interest.
Laboratory analyzed devices
Laboratory analyzed devices are samplers or dosimeters that cannot be interpreted
on-site and must be analyzed using advanced laboratory equipment. These devices
can come in the form of cartridges packed with an adsorbent, diffusion tubes with
conditioned surfaces (known as open-path or Palmes tubes), metal coupons, bags,
and canisters. The latter two options are reserved for active air sampling. The
analysis process involves extracting the collected volatile compounds followed by
identification using techniques such as gas-chromatography – mass spectrometry
(GC-MS), ion chromatography, high performance liquid chromatography (HPLC),
ultraviolet visible light (UV-Vis) spectroscopy, or electrochemical reduction
techniques. Similar to direct-read devices, such tools can be passive or active in
nature and results can be either qualitative or quantitative. Qualitative analysis will
identify the presence of compounds, while quantitative analysis will identify
compounds and their concentrations. There are examples of studies that focus on
developing laboratory analyzed samplers for cultural heritage environments, such
as a passive formaldehyde tube for use in small enclosures with low air flow
(Gibson and Brokerhof, 2001). Appendix C provides a list of standards that
describe techniques for collecting and analyzing pollutants using laboratory
devices and equipment.
Although laboratory analyzed devices require complex equipment and expertise for
interpretation, such devices can be purchased with pre-paid analysis from the
device distribution company or from air quality consultants. Some examples of
companies that sell laboratory analyzed devices with included analysis are listed
below. This list is not extensive, as there may be other available services at the
time of writing.
The Swedish Environmental Institute (IVL)
Gradko International
Dräger
Assay Technology
3M
Purafil
Camfil
For these types of devices, the sampler is mailed back to the distribution company
Strategies for Pollutant Monitoring in Museum Environments 29
after collection is performed and is then analyzed. Analysis may take several
weeks. If paired with long-term passive sampling, such a process may therefore not
be ideal for institutions in need of rapid results.
It is also possible to purchase laboratory analyzed devices that are interpreted
independently, either in-house if the appropriate equipment and expertise are
available or by an external laboratory. Like direct-read devices, there is no single
adsorbent or reagent that can collect and extract all airborne compounds.
Depending on the pollutants of interest for a study, specific choices must be made
towards the appropriate collection medium and analytical technique for
interpretation. For example, thermal desorption tubes packed with Tenax TA
adsorbent and paired with thermal desorption GC-MS are often used to collect and
analyze VOCs. Appendices I and II include examples of available devices. If
analysis in-house is not available for the above devices, they can be sent to external
labs that offer analysis as a service. For example, a list of external laboratories that
analyze Radiello tubes can be found on the Sigma Aldrich website. Collaborations
with local laboratories or institutions are also possible for passive sampler analysis
assuming they have the appropriate tools and expertise.
Laboratory analyzed devices are commonly used for heritage studies because they
can detect low pollutant concentration, can provide quantitative data, and have a
wide range of capabilities. Additionally, many laboratory analyzed devices are
manufactured as small, passive samplers or dosimeters that easily fit into display
cases or storage containers. To analyze a range of airborne compounds, researchers
use a range of devices. For example, part of the PROPAINT project included
investigating VOCs, organic acids, NO2, SO2, and O3 emissions inside painting
frames using Tenax TA tubes, IVL samplers, and a UMEx 100 formaldehyde
sampler. The Tenax TA tubes were analyzed using thermal desorption paired with
GC-MS; samplers for SO2, acetic acid and formic acid were analyzed using ion
chromatography; NO2 samplers were analyzed using photometry; formaldehyde by
HPLC; and ozone by UV-Vis spectroscopy (Lopez-Aparicio, Grøntoft and Dahlin
2010, López-Aparicio, et al. 2010).
In addition to pre-packaged devices, researchers also prepare their own samplers or
gas absorption media. Some examples include absorption of formaldehyde into
distilled water and organic acids into a NaOH solution (Schieweck, Lohrengel, et
al. 2005), and a potassium indigo trisulfonate reagent applied to a cellulose
membrane to collect ozone (Cavicchioli, et al. 2013). Another option that has been
explored in cultural heritage applications is solid phase microextraction (SPME).
SPME makes use of a thin fiber coated with an adsorbent layer that can trap
volatile molecules. Gibson et al. used solid phase microextraction (SPME) paired
with GC-MS to collect off-gassing VOCs from library collections and to measure
air quality in cultural heritage institutions throughout the United Kingdom (Gibson,
Ewlad-Ahmed, et al. 2012). Acetic acid and formic concentrations in museum
environments have also been measured using SPME (Rhyl-Svendsen and Glastrup
2002, Godoi, Van Vaeck and Van Grieken 2005).
Strategies for Pollutant Monitoring in Museum Environments 30
Laboratory analyzed devices are generally more expensive and complex than
direct-read devices, but offer benefits. Primarily, they are more sensitive and
compound specific than direct-read samplers, although it should be noted that
laboratory analyzed adsorbents and reagents are prone to interference issues as
well. Interpreting results requires more in-depth knowledge of atmospheric
environments. Additionally, the collection and analysis processes for laboratory
analyzed devices are fairly lengthy and can last several weeks if passive collection
is used. Lengthy collection times for museums can be beneficial as this provides a
time-averaged assessment of an environment, but may not always be practical.
Qualitative vs. quantitative devices
The production of qualitative or quantitative data does not depend entirely on the
device used. It can also depend on the analysis process. Some devices, for example
the A-D Strip, are purely qualitative because their response is simply based on a
color change. Other devices, primarily laboratory analyzed devices, can produce
qualitative or quantitative data. For example, using GC-MS to analyze the
compounds trapped on to a thermal desorption tube produces qualitative data if
peaks are only identified. By incorporating a standard calibration into the analysis
process, such peaks can also be quantified.
Before deciding on an air quality monitoring technique, it is necessary to decide the
kind of data that is useful for your institution. Qualitative data is often easier to
understand. Conversely, quantitative data requires deeper knowledge of air quality
analysis and appropriate pollutant concentrations for your particular institution and
situation. As discussed under Guidelines for pollution levels, data for quantitative
analysis is presented in either gravimetric units (µg/m3, mg/m3) or volumetric units
(ppm, ppb). These units can be converted to each other if the temperature and
pressure are known.
Sensor networks
In recent years, a number of cultural heritage institutions have either developed or
collaborated with industry to implement sensor networks that detect pollutant
levels. Museums often install temperature and humidity sensors as part of overall
environment control, but pollutant detection is far less common. Several
institutions have investigated the possibility of creating affordable, commercially
available pollutant sensor networks that can be installed at any museum. At this
time, technology intended for cultural heritage applications is not yet commercially
available. Sensor networks are highly useful for monitoring pollutants as the
sensors themselves can be inconspicuously placed in many different locations,
creating a communication infrastructure. Each sensor provides continuous
cumulative and real-time data through its connection to a centralized server. This
server can then alert museum personnel to air quality issues. The following section
describes some examples of sensor networks that have been used in museum
environments.
Some existing sensor networks incorporate dosimeter technology such as quartz
Strategies for Pollutant Monitoring in Museum Environments 31
crystal microbalances and metal coupons. The Cloisters branch of the Metropolitan
Museum of Art collaborated with IBM to develop a highly dense sensor network
based on the corrosion of metal coupons. Sensors were installed at multiple points
in five separate galleries throughout the building, all of which were wireless. Using
an IBM-developed software platform, the corrosion rate of the coupons was
calculated in real-time to assess the environmental air quality (Klein, et al. 2017).
Additionally, a set of piezoelectric quartz crystal microbalances coated with
different metals were installed at Apsley House in London and at the Royal Palaces
of Abomey in Benin. The microbalances also contained a wireless communication
module that allowed for real-time visualization of the air quality data (Agbota,
Mitchell, et al. 2014).
The National Archives of Korea developed a wireless sensor device composed of
several smaller sensors, each of which individually measures a set of compounds.
A light scattering sensor was used to detect particulate matter; an electrochemical
sensor was used to measure for SO2, CO, NOx, and formaldehyde; and a photo
ionization sensor to measure for VOCs. All individual sensors were then combined
and integrated to create the monitoring device that transmits data wirelessly to a PC
(C.-y. Lee 2012).
Pollution monitoring practices in museums
Before beginning a pollution monitoring project, it is important to consider a
number of practical elements. Such elements include choosing the appropriate
device and determining the time and deployment location for devices. There are
many available techniques for monitoring gaseous pollutants in museum
environments. Many of these techniques are adopted from industry or human
health and safety practices, while some were developed specifically for cultural
heritage applications. To determine which techniques are most suitable for a
monitoring project, one must consider some parameters:
Budget
Timeline
Physical considerations
Existing collections issues
Desired data outcome
Available personnel and resources
The issues of budget and timeline were generally discussed in the previous section
describing different types of monitoring devices. To generalize, passive samplers
are typically less expensive than active samplers as they do not require the use of
pumps. Direct-read devices are less expensive than laboratory analyzed devices
because the latter require the cost of analysis. The time required for passive
sampling is much longer than that required for active sampling as the use of pumps
significantly decreases collection time. Active sampling results provide a
“snapshot” of the measured environment at a certain point in time, while passive
sampling provides longer-term, time-averaged information about an environment.
Strategies for Pollutant Monitoring in Museum Environments 32
For laboratory analyzed devices it is important to factor in the time required for
analysis. This can last several weeks, particularly if the devices are mailed to an
external laboratory.
Physical considerations take into account the available space in the measured
environment. Cultural heritage institutions are often interested in measuring
microenvironments such as the interiors of display cases or storage containers. It
therefore may be difficult to incorporate active sampling devices into such
enclosed spaces with limited room. Many passive devices are small in size and can
therefore be easily placed in microenvironments without issue. Some devices
require a particular orientation during collection and may need physical supports,
which may affect where the devices can be placed. For example, DSD-DNPH
aldehyde samplers are best used hanging from an overhead support to maintain a
vertical orientation and eliminate contact with the sensitive diffusive collection
membrane (Sigma-Aldrich 2017). It is necessary to consult the manufacturers for
orientation information and physical support options.
The device chosen for a particular project also depend greatly on collection issues
that require attention. Such issues determine what pollutants should be monitored.
As many sampling devices can only effectively collect certain classes of volatile
compounds, it is necessary to identify the pollutants that are of greatest risk to the
collection, particularly if the budget is limited. For example, if a building uses
natural ventilation with no filtration, it may be of interest to study the
concentrations of outdoor pollutants in gallery spaces. Such pollutants include
sulfur dioxide (SO2), ozone (O3), and nitrogen oxides (NOx). As another example,
if wood-based materials are used in gallery spaces, display cases, or storage
compartments, it is important to test for acetic acid gas concentrations. It is
therefore necessary to develop a strong knowledge of the construction materials
used in a certain environment as well as the collection materials and their
vulnerabilities.
Finally, one must determine the kind of results that are most useful to the collection
and institution. For instance, exact concentrations in parts per billion or µg/m3 may
not be necessary to determine if there is a large acetic acid problem inside a display
case. Results from qualitative direct-read devices are rapid and easy to interpret.
They do not require in-depth knowledge on pollutants, but are generally not as
sensitive and do not provide as much information as quantitative devices. Data
from quantitative devices requires greater knowledge about appropriate pollutant
levels for an environment, interactions between pollutants and cultural materials,
and interactions between different airborne pollutants. Some commercially
available devices may not be sensitive enough to detect very low pollutant
concentrations. As an example, hydrogen sulfide will corrode silver materials at the
parts per trillion levels, yet most devices cannot detect concentrations this low. It is
therefore important to be aware of a device’s limitations before choosing it for a
monitoring project.
Some practical aspects of pollution monitoring projects in museums include
Strategies for Pollutant Monitoring in Museum Environments 33
determining where to place the devices, when to perform the monitoring, the
number of devices, and documentation. Measurement location and deployment
schedule should attempt to be representative of the long-term environment of the
monitored area. In gallery spaces, devices would ideally be placed one meter above
ground and centrally located, but this is not always possible. It is nevertheless
important to place the devices in locations that are not too close to walls, air vents,
windows, or doors. In microenvironments such as display cases it is important to
have the enclosure open for as little time as possible during deployment. There is
no specified period when devices should be deployed, but as mentioned previously,
the time frame should be representative of the long-term environment. It is
therefore good to avoid collecting during times of construction or heavy cleaning
unless there is a specific desire to measure during these moments. It is often useful
to perform comparative air quality assessments. For example, performing two
separate assessments, one before a large renovation and one after, will provide
valuable information on how the environment of the museum has changed as the
result of alterations to the space. It is recommended to perform air quality
assessments after large renovations, or when significant amounts of new materials
are added to an environment.
Typically, only one of each type of device is necessary for a space, whether it is a
large gallery or the interior of a display case. It may be necessary to purchase a
blank along with the deployable air samplers. These blanks are not deployed with
the rest of the samplers and are therefore stored unopened during the collection
period. In the case of laboratory analyzed air samplers, the blank is returned with
the rest of the devices and will provide information on shipping and storage
conditions of the sampler batch. Finally, it is necessary to document all steps of the
monitoring process and record environmental parameters. Such information helps
external laboratories perform analysis of the sampler, and aids with results
interpretation. On the deployment date, one should record the following:
temperature
humidity
deployment date and time
measurement location
materials in the surrounding environment (both construction and
collection materials)
placement of windows, doors, or air vents
information on local pollutants (from smoking areas, food preparation
areas, etc.)
any smells present
use of an HVAC system and/or pollution filtration
difficulties with deployment.
During the collection period, it is important to maintain awareness of any
significant fluctuations in temperature and humidity. One must also record changes
to the environment, including noticeable smells, construction, cleaning, HVAC
Strategies for Pollutant Monitoring in Museum Environments 34
functionality, etc. It is also necessary to inform staff of the experiment to ensure
that devices are not disturbed during collection time. During the retrieval process,
one must record the time and date of retrieval. The exposure time is needed to
calculate quantitative results. Laboratory analyzed devices will need to be closed or
capped in some way to stop the collection of gases and returned to their respective
companies.
Mitigation techniques
If a pollutant issue is detected, or if an object requires preventive action, there are a
number of techniques to mitigate the effects of harmful volatile compounds.
Pollutants can be sorbed, isolated, diluted, and slowed. The process of adsorbing
pollutants involves incorporating a material with a reactive surface into an
environment. This reactive surface will interact with volatile compounds to trap
and filter them from the surrounding environment. Such examples include
activated charcoal, silica gel, activated alumina, and zeolites. Some adsorbents
such as activated charcoal are known as general scavengers, as they are able to
collect and trap a range of volatile compounds. Some are tailored for more specific
purposes and pollutants, such as Purafil’s line of chemical media (Purafil n.d.).
Adsorbent materials are sold in many forms, including loose granular pellets,
woven cloth, paper materials, and paint. As part of the MEMORI project, scientists
at the Fraunhofer Wilhelm-Klauditz-Institute WKI and the Tate studied a number
of adsorbing materials, including activated granulated carbon, carbon cloth, and
zeolites. These tests investigated the materials’ chemical properties, adsorbing
properties, and potential for desorption, paying particular attention to the removal
of formaldehyde, formic acid, acetic acid, toluene, and alpha-pinene. Activated
charcoal and alkaline-impregnated activated charcoal had the best pollutant
adsorption properties. It was also found that adsorbing media can desorb VOCs
under changed environmental conditions. The researchers from the Fraunhofer
Institute are in the process of investigating the adsorbent properties within museum
cases, monitoring for pollutant levels within the enclosures over time (Schieweck
och Hackney n.d.). It should be noted that adsorbents will become exhausted after
time and require replacement or cleaning. Sorbing processes also occur on surfaces
such as gallery walls, objects, and display case surfaces. Different types of
materials will absorb pollutants at different rates. For example, a study by Walsh,
et al. found that sulfur dioxide has a higher deposition velocity on emulsion paint
than on glossy paint, thus indicating that the emulsion paint sorbed more of the
pollutant (Walsh, et al. 1977). One could therefore reduce pollutants by increasing
the availability of surfaces in a room.
Isolating pollutants involves the use of barriers in the form of heat-sealed polymer
films, liquid sealants, or powder coatings to cover problematic construction
materials (Thickett, et al. 2004). Medium density fiberboard (MDF) is an example
of a material that is commonly used to construct display cases but is also known to
emit high levels of acetic acid. It is therefore necessary to coat MDF boards to
reduce or remove its acetic acid emissions from the surrounding environment. The
effectiveness of a barrier is dependent on its composition as well as the application
Strategies for Pollutant Monitoring in Museum Environments 35
method. Before using a coating, it is advised to test its suitability in museum
environments. An effective barrier coating is one that will not adversely react with
the material it is coating, does not permit diffusion of gas molecules through the
film, and forms a surface film on the material rather than penetrating it (Tétreault
1999). Further information on barrier coatings can be found in the Canadian
Conservation Institute Technical Bulletin No. 21, Coatings for Display and
Storage in Museums” by Jean Tétreault and in a review paper from the British
Museum (Korenberg and Bertolotti 2019)
Pollutants can also be reduced through changes in the environment. By increasing
ventilation and air exchanges in a space, pollutants can be diluted. Macro-
environments such as galleries usually have lower pollutant levels than small,
enclosed spaces due to their large volumes and high air exchange rates. Reaction
rates between pollutants and collection objects can also be reduced by lowering
temperatures and relative humidity in a given space. It should be noted that while
this environmental change can reduce pollution reaction rates, objects may
adversely react to changes in temperature and humidity in other ways, causing
issues like cracking and delamination.
In addition to the above discussion, members of the MEMORI project created a
thorough decision support model for cultural institutions to help identify materials
that are at risk to pollution exposure, and poses questions to help institutions
determine the type of mitigation techniques that are most valuable to their
collection. These decision tools are available through the MEMORI website:
http://memori.nilu.no/Additional#decision-tools.
Strategies for Pollutant Monitoring in Museum Environments 36
Pollutant monitoring at Nationalmuseum
Motivation
Nationalmuseum underwent a multi-year renovation of its galleries, incorporating
many new materials. In addition, new display cases were installed to house objects
on display. The museum staff intended to ensure that both gallery and display case
environments were safe for collection objects. Riksantikvarieämbetet performed
Oddy tests of many construction and design materials used during the renovation to
screen for common corrosive emissions. The Oddy test involves enclosing a
sample material, three metal coupons (silver, copper, and lead), and a small amount
of water inside a sealed glass boiling tube. Over time, corrosion products may form
on the metal coupons, indicating the classes of volatile compounds produced by the
sample material. Such tests are accelerated and require the use of elevated
temperature and humidity – conditions that are not found in controlled museum
environments. They are therefore not fully indicative of realistic long-term storage
and display conditions. In addition to the Oddy tests, material emissions were
further studied through passive sampling of volatile pollutants in Nationalmuseum
galleries and display cases. Unlike Oddy tests, passive sampling tests react with
gases under in-situ environmental conditions. The samplers are small and
inconspicuous, and are easily placed within galleries and display cases. After
collection and analysis, the results provide information on specific gases and in
some cases their concentrations. For the passive sampling tests, four different
gallery spaces and three completed display cases were investigated. The sampling
schedule was split into two collection sessions, the first of which began in January
2018 and measured only gallery spaces, the second of which began in May 2018
and measured both galleries and display cases. The choice to perform two separate
collections was based on the arrival schedule of the display cases. It also provided
an excellent opportunity to measure the same gallery spaces at different times
during the renovation process. Information from the samplers can indicate if
materials within the galleries and display cases are emitting harmful gases, as well
as their concentrations. Additionally, gallery samplers can indicate how effective
the museum building is at filtering outdoor pollutants. These results will inform the
museum staff if there is a need for further pollution mitigation strategies.
Materials and methods
Passive sampling devices from three separate institutions were used: the Swedish
Environmental Institute (IVL), Gradko International, and Purafil. These institutions
were chosen because their sampling devices are inexpensive, sensitive to low
concentrations of pollutants, and are easily returned to their respective companies
by mail for analysis. There is no single passive sampling device that adsorbs all
volatile compounds, thus seven separate samplers were purchased. The names,
detectable gases, and detection limits at maximum exposure time of the seven
samplers are provided in Table III.
Strategies for Pollutant Monitoring in Museum Environments 37
Table III: Information on passive samplers purchased for Nationalmuseum monitoring study
Sampler name Detectable
gases
Detection
limits (µg/m3)
Detection
limits (ppb)
Proposed
exposure
time (days)
IVL VOC Tenax
benzene
toluene
n-octane
ethyl benzene
m+p-xylene
o-xylene
butyl acetate
n-nonane
0.18100
0.2090
0.13100
0.0970
0.32150
0.1270
0.5070
0.12120
7
IVL Acid Gases
sulfur dioxide
formic acid
acetic acid
hydrochloric acid
0.1100
1.5150
1.5250
0.3100
0.0435
0.870
0.6100
0.260
28
IVL Ozone (O3) ozone 1–100 0.550 28
IVL Aldehyde formaldehyde 0.05210 0.04170 7
IVL NOx nitrogen dioxide
nitrous oxide
0.1200
0.2300
0.05100
0.2240 28
Gradko H2S hydrogen sulfide 0.1 0.071 28
Purafil CCC
Sulfides,
chlorides, oxides
N/A N/A 2890
The samplers from IVL contain adsorbents inside compact containers, the Gradko
H2S samplers are Palmes diffusion tubes with a reactive interior surface, and the
Purafil Corrosion Classification Coupons (CCC) are reactive silver and copper
surfaces. For the IVL and Gradko devices, the detection limits are dependent on the
exposure time. The longer the exposure time, the lower the detection limit.
Maximum exposure time for the acid gas, ozone, NOx and H2S samplers is four
weeks. For the VOC and formaldehyde samplers, maximum exposure time is one
week. As measuring even low levels of pollutants was of interest, each sampler
was exposed for the maximum length of time to achieve the lowest detection limits.
As mentioned previously, the sampling process was divided into two separate
collection sessions. The first session involved measuring four different gallery
spaces, each of which contained one of each IVL sampler and one Gradko H2S
sampler. The Purafil coupons were not included in the first session. The second
session involved measuring two different galleries and three different display
cases. The galleries from the second session were also measured in the first, and
contained one of each IVL sampler as well as one Gradko H2S sampler. The
display cases measured were located within the measured galleries, each of which
contained one of each IVL sampler, one Gradko H2S sampler, and one Purafil CCC
sampler. As the display case environments contain enclosed objects and are more
susceptible to corrosive gas buildup, it was deemed necessary to use the Purafil
Strategies for Pollutant Monitoring in Museum Environments 38
coupons to test for the presence of other gases such as various sulfides, chlorides,
and oxides. In addition to the samplers, two Gradko reference blanks were also
purchased, one for each sampling session. In total, nine separate measurements
were made over the course of the project. Tables IV and V provide information on
each measured area and the samplers used.
As discussed previously, the sampling rate of passive air samplers is affected by
low airflow. Such was the case inside the display cases measured in this study. Due
to the need to maintain climatized atmospheres inside the cases and the
construction of the display case openings, it was determined that active sampling
would not be appropriate for these microenvironments. The decreased sampling
rate is therefore taken into consideration for the display case measurements.
Additionally, if a sampler is used in an indoor environment, IVL and Gradko
account for such low airflow situations when calculating the airborne pollutant
concentrations.
Table IV: Descriptions of each space measured, the sessions during which they were measured, and
the samplers used during collection.
Location Session 1 Session 2 Description
Gallery 1 VOC, Acid, O3,
Ald*, NOx, H2S Large gallery. Contained plastic sheeting,
plastic and wooden containers at time of
sampling.
Gallery 2 VOC, Acid, O3,
Ald*, NOx, H2S
Large gallery. Contained plastic sheeting,
large painting, and work tools at time of
sampling.
Gallery 3 VOC, Acid, O3,
Ald*, NOx, H2S
VOC, Acid, O3,
Ald, NOx, H2S
Small cabinet gallery. Empty during
session 1, contained objects during
session 2.
Gallery 4 VOC, Acid, O3,
Ald*, NOx, H2S
VOC, Acid, O3,
Ald, NOx, H2S
Large gallery. Empty during session 1,
contained objects during session 2.
Case A VOC, Acid, O3,
Ald, NOx, H2S,
CCC
Located in gallery 4. Contains objects
(silver, textile, wood, ceramic) and
painted steel base.
Case B VOC, Acid, O3,
Ald, NOx, H2S,
CCC
Located in gallery 3. Contains objects
(silver, copper, bronze, wood, porcelain,
glass).
Case C VOC, Acid, O3,
Ald, NOx, H2S,
CCC
Located in gallery not previously
measured. No objects, but contains steel
base plate painted by case manufacturer.
* These aldehyde samplers were lost during transportation back to IVL. Their results are not
available.
Strategies for Pollutant Monitoring in Museum Environments 39
Table V: Descriptions of each space measured, the sessions during which they were measured, and
the samplers used during collection.
Sampler
Session 1 exposure days
Start: Jan. 18
th
2018
Session 2 exposure days
Start: May 4
th
2018
VOC 7 4
Acid 28 31
O3 28 31
Ald 7 4
NOx 28 31
H2S 28 31
CCC N/A 116
On the first day of sampling for each session, RAÄ employees traveled to
Nationalmuseum to assist with the sampler setup. All samplers were deployed
simultaneously. On the final day of collection for each respective sampler, a
Nationalmuseum employee performed the retrieval process and mailed each
sampler to its appropriate company. For the first collection session beginning
January 18, all samplers were supported using a metal holder provided by IVL, an
image of which is shown in Figure 1.
Figure 1: An example of the setup logistics for the first session of measurements at the
Nationalmusuem. Includes samplers from IVL (NOx, O3, aldehydes, acid gases, VOCs), a Gradko H2S
sampler, and the metal holder from IVL. Photograph by Kriste Sibul/Nationalmuseum.
This holder was not self-supported and therefore had to be adhered to a flat surface
using tape in galleries 1, 2, and 4. The metal holder was hung from a speaker in
Strategies for Pollutant Monitoring in Museum Environments 40
gallery 3. During the retrieval process, Nationalmuseum employees noted that the
samplers were difficult to remove from the metal holder and therefore requested a
simpler system for the second session. Additionally, the Gradko samplers were
adhered to the metal support using adhesive tape provided by Gradko. The
adhesive of one Gradko sampler failed during the first collection period and the
sampler remained on the ground for 1 – 3 days. It was therefore determined that the
adhesive tape should not be used for the second session. The VOC and aldehyde
samplers were allowed to collect for 7 days, while the O3, NOx, acid gas, and H2S
samplers collected for a total of 28 days. Unfortunately, the aldehyde samplers
were lost during transportation back to IVL. The results for these samplers are
therefore not available.
The second session began May 4 and again involved sampler setup by RAÄ
employees. As is noted in Table IV, galleries 3 and 4 were measured in both
sessions. During the first session both galleries were empty, but by the second
session, many of the museum collection objects had been installed, both in display
cases and in the galleries. The objects varied greatly in medium and material type,
including paintings, tapestries, ceramics, metal, and stone sculpture among other
things. In addition to the collection objects, a number of display cases composed of
metal and glass had been installed as well as platforms potentially made of painted
medium density fiberboard. Two of the display cases measured during session two
contained museum objects of a great variety of media and material type. Both
display cases were located in previously measured galleries and were climatized.
Upon opening both display cases, a solvent-like smell was noted.
Rather than using the metal holder from IVL for the second session, the samplers
were either placed directly on a flat surface in the measured environment (acid gas,
NOx, ozone, and CCC), upside down inside a small glass beaker (VOC), or
suspended by string from a small glass support (aldehyde and H2S). Due to some
time and staff constraints, the VOC and aldehyde samplers were only able to
collect for four days during the second session. This would only affect the
sensitivity of the samplers and their ability to detect very low concentrations.
Additionally, the O3, NOx, acid gas, and H2S samplers collected for 31 days. The
Purafil CCC samplers remained inside the display cases for a total of 116 days.
Display case C had to remain open after the samplers were deployed and they were
therefore exposed to the internal case environment as well as the surrounding
environment in the gallery.
Strategies for Pollutant Monitoring in Museum Environments 41
Figure 2: An example of the setup logistics for the second session of measurements at
Nationalmusuem. Includes samplers from IVL (NOx, O3, aldehydes, acid gases, VOCs), a Gradko H2S
sampler, and a Purafil Corrosion Classification Coupon. Photograph by Kriste Sibul/Nationalmuseum.
Results and discussion
Table VI provides results from all passive samplers that collected during session 1.
All data is presented in units of µg/m3. Where indicated, outdoor concentrations
were calculated from public data available through SLB Analys (Stockholm Air
and Noise Analysis), a Stockholm-based company that measures local air quality.
Their Torkel Knutssonsgatan station, positioned approximately one kilometer from
Nationalmuseum, measures hourly atmospheric concentrations of ozone (O3) and
nitrogen oxides (NOx), and averages of sulfur dioxide (SO2). The values given for
outdoor SO2 and outdoor NO2 from SLB are the reported yearly averages from
2017. Outdoor levels not from SLB and suggested collections limits in Table VI
were taken from the compiled data from urban areas in Grzywacz’s book
Monitoring for Gaseous Pollutants in Museum Environments (Grzywacz 2006).
The values measured by SLB for NOx, O3, and SO2 are lower than those measured
inside Nationalmuseum. In comparison, the concentrations of indoor nitrogen
dioxide are closer to the outdoor level, sometimes exceeding the outdoor average
measured by SLB. Ozone is known to react rapidly with nitrous oxide to produce
nitrogen dioxide. On occasion nitrogen dioxide concentrations inside museum
galleries have been found to exceed outdoor concentrations (Brimblecombe,
Blades, et al. 1999). Indoor concentrations of ozone and nitrogen dioxide in Table
VI are low compared to levels commonly measured in museum galleries. Based on
Strategies for Pollutant Monitoring in Museum Environments 42
existing literature, indoor concentrations of ozone in museums and galleries are
typically below 60 µg/m3 and nitrogen dioxide concentrations below 47 µg/m3 (M.
Rhyl-Svendsen 2006). Both formic and acetic acid levels in the Nationalmuseum
galleries are below maximum suggested collection limits, although the concentration
of acetic acid in gallery 4 is twice as much as the concentrations in the three other
galleries. This could be due to materials and paints used inside the galleries. Wood
products, for example, produce high levels of acetic acid. Nevertheless, the concen-
trations for gallery 4 are still acceptable. Acetic and formic acids concentrations in
the galleries are on par with levels typically found in studies of museum environ-
ments. Gallery concentrations have been found to range between 0.6 and 99 µg/m3
for formic acid and 37 to 415 µg/m3 for acetic acid (Robinet, et al. 2004, Grzywacz
and Tennent 1994, Schieweck, Lohrengel, et al. 2005, Kontozava, et al. 2005).
Table VI: Compiled data (all in µg/m3) from the samplers deployed in the galleries of the
Nationalmuseum during session 1 (January 18 February 15).
Compound Gall. 1 Gall. 2 Gall. 3 Gall. 4 Outdoor
Suggested
collections
limits B
NOx 16.18 19.61 16.29 15.97 23.5 A
NO2 11.10 13.46 11.04 10.27 11A 4–19
NO 3.32 4.02 3.43 3.72 2–40 B
O3 < 1.0 < 1.0 1.5 < 1.0 40.0 A 1–10
SO2 < 0.2 < 0.2 < 0.2 < 0.2 0.4A 1–5
Acetic acid 20.63 14.72 17.29 42.28 0.240 B 100697
Formic acid 31.23 28.40 36.22 31.10 0.0432 B 1038
Acetaldehyde - - - -
Formaldehyde - - - -
H2S 0.17 < 0.01 0.05 0.02 0.17 B < 0.141
Benzene 0.76 0.76 0.79 0.85
Toluene 47 11 2.9 24
Butylacetate 2.4 1.1 17 3.5
n-Octane 1.6 0.88 0.95 1.4
Ethylbenzene 0.76 0.65 1.1 0.83
m+p-Xylene 3.3 3.2 4.1 3.9
o-Xylene 2.3 2 2.1 2.5
n-Nonane < 0.12 < 0.12 < 0.12 < 0.12
ƩVOC (n-hexane)
< 357
A = Calculated data from SLB Analys
B = Data from Grzywacz 2006
- = Data not obtained
Strategies for Pollutant Monitoring in Museum Environments 43
As mentioned previously, the aldehyde samplers were lost during transit and could
therefore not provide any data from session 1. Hydrogen sulfide levels are low for all
galleries except gallery 1. As the museum was undergoing construction and the room
contained a variety of materials for building and transport, slightly elevated H2S
concentrations could be due to a number of factors. When construction is complete it is
recommended that further monitoring should be performed in this gallery, perhaps using
a simple tool that easily reacts to hydrogen sulfide such as a polished silver coupon or a
Purafil CCC device. From a human health perspective, the only VOCs of concern in the
galleries are toluene and butylacetate. Toluene levels are high only for the galleries in
which duct tape was required to support the metal stand provided by IVL, therefore
suggesting that the adhesive likely emitted toluene during collection. Butylacetate
concentrations are high in gallery 3. It is unclear the origin of butylacetate in this gallery,
but one suggestion is that it stems from VOCs produced by the paint used to paint the
gallery walls. During setup in gallery 3 the smell of fresh paint was noted. Additionally,
the HVAC system was not functioning in this area of the museum during the collection
period, potentially leading to a buildup of volatile compounds in the gallery. There are
currently no reported issues between butylacetate and cultural heritage.
Gradko and IVL data from session 2, which began May 4 and included both gallery and
display case measurements, is given in Table VII. Data from the Purafil coupons are
presented slightly differently as they measure corrosion film thickness, and are given in
Table VIII. As mentioned previously, case A was located in gallery 3, case B was located
in gallery 4, and case C was located in a gallery that was not measured. Both galleries 3 and
4 were also measured in session 1. As in Table IV, all measurements are in units of µg/m3
and outdoor levels for the measurement period were retrieved from SLB where indicated.
Table VII: Compiled data (all in µg/m3) from the samplers deployed in the galleries and display cases of
Nationalmuseum during session 2 (May 4June 4).
Compound Case A Gall. 3 Case B Gall. 4 Case C Outdoor
Suggested
collections
limits
B
NOx 35.9 14.6 36.1 15.0 12.4 15.6 A
NO2 2.43 11.30 1.94 10.95 3.90 11A 4 - 19
NO 21.86 2.18 22.34 2.63 5.59 2 40 B
O3 1.8 1.5 <0.1 4.3 <0.1 80.7 A 1 - 10
SO2 <0.2 <0.2 <0.2 <0.2 <0.2 0.4A 1 - 5
Acetic acid 19.89 88.85 18.87 91.62 3.02 0.2 40 B 100 - 697
Formic acid 11.61 47.63 17.60 53.94 6.62 0.04 32 B 10 - 38
Acetaldehyde 110 22 78 23 37 6 31 B
Formaldehyde 28 30 23 27 6.7 0.5 30 B 13 - 25
HCl <0.3 <0.3 <0.3 <0.3 <0.3
H2S 0.09 0.08 0.08 0.08 0.08 0.1 7 B < 0.141
A = Calculated data from SLB Analys
B = Data from Grzywacz 2006
Strategies for Pollutant Monitoring in Museum Environments 44
Table VIII: Compiled data from the Purafil coupon deployed in the three display cases of
Nationalmuseum during session 2 (May 4 August 28). The results are presented as corrosion
thickness formed over 30 days.
Corrosion product Case A Case B Case C
Cu2S/30 days (nm) 0 0 0
Cu2O/30 days (nm) 9.7 7.4 5.1
Cu unknowns/30 days (nm) 0 0 12.9
AgCl/30 days (nm) 0 0 0
Ag2S/30 days (nm) 9.1 5.0 2.5
Ag unknowns/30 days (nm) 0 0 0
Estimated H2S level 4 - 14 µg/m3 < 4 µg/m3 4 - 14 µg/m3
Compared to the gallery measurements for session 1, the concentrations of NO2,
SO2, HCl, and H2S in galleries 3 and 4 during session 2 remained approximately
the same. Ozone levels appeared to increase slightly, which could be due to the
noticeable increase in ozone concentration measured outside during that time.
Ozone levels inside the museum are still significantly reduced from outdoor levels.
Acetic acid and formic acid levels both increased in the galleries during session 2.
This could be due to the incorporation of new building materials into the galleries
between February and May. As mentioned previously, a number of support
structures in the galleries may have been composed of medium density fiberboard
(MDF), although this is not confirmed. MDF, like all wood-based products, emit
acetic acid, formic acid, acetaldehyde, and formaldehyde. Additionally, new paints
used in the galleries may also have had an effect on the acetic and formic acid
concentrations. The acetic acid levels are lower than the suggested collection limits
provided by Grzywacz, but the formic levels in the galleries are slightly higher. As
the construction materials within the galleries were quite new during the time of
measurement, it is possible that these concentrations will decrease over time after
sufficient off-gassing has occurred. Nevertheless, it is suggested to periodically
monitor collection objects susceptible to corrosion such as lead, lead-containing
bronzes, calcareous objects (shell, bone, limestone, etc.), and cellulose objects. It is
also beneficial to periodically monitor for acetic and formic acid in the galleries.
This can be done using simple tools such as an A-D Strip (away from light
exposure), a polished lead coupon, active air sampling, or passive samplers like
those from IVL.
Display cases A and B both contain objects, while case C was empty besides a
painted steel base plate. Nationalmuseum employees chose to keep case C open
during measurements due to a noticeable solvent-like smell. The air measured by
the samplers in case C is therefore a mix of the gallery air and the display case
environment.
Concentrations for nitric oxide (NO) inside cases A and B are greater than those for
the surrounding galleries. Additionally, the NO concentration inside case C was
Strategies for Pollutant Monitoring in Museum Environments 45
lower than the object-containing cases. This indicates either that something within
case B and A is producing nitric oxide gas, whether it be an object or a case
construction material, or that nitric oxide in the galleries is being absorbed or
oxidized. Both cases A and B emitted a solvent-like smell when opened. If nitric
oxide is being produced within the display case, its source may be difficult to
determine as NO in atmosphere is a radical and rapidly oxidizes to form NO+ or
combines with oxygen to form NO2. Most nitrogen oxides are produced as the
result of combustion from engines, cigarettes, or stoves – processes that are not
likely to be found inside a display case.
Concentrations of acetic acid, formic acid, and formaldehyde are lower in all of the
display cases than in the galleries. Cases A and B contain objects at least partially
composed of wood, which could explain the higher concentrations of acetic acid
compared to case C. Other sources could include paints used to coat the display
case base and shelves. Acetic and formic acids can also form in indoor
environments as the product of ester hydrolysis, a reaction that is the result of
volatile emissions interacting with each other. For example, 2-ethylhexylacetate, a
high boiling point solvent found in indoor materials, can react with atmospheric
water to hydrolyze, producing 2-ethyl-1-hexanol and acetic acid (Uhde and
Salthammer 2007). While the acetic and formic acid levels are not high enough to
require immediate action, it is possible that these concentrations could increase
over time. Additionally, formaldehyde may oxidize to create formic acid. In
display cases that contain wooden objects it is important to ensure that other
surrounding objects are not highly sensitive to organic acid gases. If sensitive
objects are present, it may be necessary to mitigate the risk of corrosion through
using adsorbent media (e.g. activated charcoal) and periodic monitoring (either
visually or by means of a tool). Levels of acetaldehyde in the object-containing
cases are higher than in the galleries and the empty case. Interactions between
acetaldehyde and cultural objects are not well documented and may pose no threat,
but it can oxidize to form acetic acid in the presence of an oxidant such as ozone or
peroxide (Grzywacz 2006).
In studies of newly manufactured display cases containing wooden base plates,
levels of acetic acid, formic acid, and formaldehyde have been found to be much
higher than those exhibited by Nationalmuseum cases. In measurements ranging
from 1 day to 7 days post-manufacture, acetic acid concentrations were between
397 and 2294 µg/m3, formic acid between < 12 and 80 µg/m3, and formaldehyde
between 15 and 70 µg/m3. Additionally, most individual VOCs measured inside
new display cases ranged from 50 to 1000 µg/m3. Older showcases also gave
higher formaldehyde and organic acid concentrations than those presented in Table
VII. Cases approximately 3 – 4 months old had acetic acid concentrations between
316 and 876 µg/m3, formic acid between 95 and 348 µg/m3, and formaldehyde
between 29 and 52 µg/m3 (A. Schieweck 2009, Schieweck and Salthammer 2011).
Despite the smaller concentrations found in Nationalmuseum cases, even low
levels of acetic and formic acid can cause deterioration. As an example, lead
formate corrosion products were found on lead museum collection objects in a
Strategies for Pollutant Monitoring in Museum Environments 46
storage room containing a low concentration of formic acid (2.66 µg/m3)
(Hatchfield 2002).
Data from the Purafil Corrosion Classification Coupons (CCC) focuses on gaseous
compounds that react with silver and copper to form corrosion products. Such
gases include reduced sulfur emissions (H2S, carbonyl sulfide) and chlorine
emissions (i.e. HCl) for both copper and silver, as well as oxygen and sulfur
dioxide for copper. While the data was collected over a period of 116 days, Purafil
presents all of their CCC results in a standardized format that estimates the
corrosion buildup over a 30 day period. This data can then be extrapolated to
predict corrosion buildup over the course of 1 year, 5 years, etc. For all display
cases in Table VIII, there was measurable copper oxide (Cu2O) and silver sulfide
(Ag2S) present. This is to be expected as copper forms a natural oxide when
exposed to oxygen, and silver is highly reactive to very low atmospheric
concentrations of hydrogen sulfide, producing Ag2S (Rice, et al. 1981). Case C also
contained other unidentified corrosion products on its surface. As this display case
was open for the majority of the Purafil CCC collection period, the unidentified
compounds could be due to pollutants from the gallery or due to humidity.
Renovation and installation was still on going in the gallery during collection,
likely producing dust particles and pollutants. According to Purafil, acceptable
museum air quality specifications include a silver sulfide (Ag2S) thickness of 5
nm/30 days, silver oxide (Ag2O) thickness of 5 nm/30 days, no silver chloride
corrosion, copper oxide (Cu2O) thickness of less than 15 nm/30 days, and no
sulfur-based copper corrosion evident (Muller 2011). Case B meets this
specification, but cases A and C do not. Case C does not meet the specification due
to the presence of unidentified copper compounds, but this again may be due to
humidity or dust deposition from the gallery. Case A silver sulfide corrosion is just
slightly higher than the specification, and therefore may require further monitoring
if the case contains sensitive objects made of silver. Silver will visibly tarnish in
the presence of normal H2S levels. If silver is present in such a case, it may
therefore be advisable to incorporate an adsorbent into the display cases. Along
with corrosion thickness measurements and identification, Purafil estimates the
possible air concentration of H2S gas during collection, also presented in Table VI.
These estimated concentrations are within the limits of normal atmospheric H2S
concentrations.
Strategies for Pollutant Monitoring in Museum Environments 47
Conclusions
This report reviewed a number of pertinent issues relating to monitoring cultural
heritage collections. Such subjects include volatile pollutant relevant to cultural
heritage preservation, existing technology suitable for heritage environments, and
practical monitoring techniques. This information is applicable to all institutions as
pollutant issues can be found in any environment. Additionally, the tools discussed
range greatly in price, accessibility, and ease of use. Depending on budget, time,
and personnel, institutions can choose simple and inexpensive techniques (e.g.
metal coupons and A-D strips) or more complex devices (e.g. laboratory analyzed
samplers). As the field of preventive preservation grows, more products tailored
specifically for cultural heritage will perhaps become commercially available and
affordable.
In addition to the literature review, a pollutant monitoring case study was
performed at Nationalmuseum in Stockholm. As the museum was undergoing a
renovation and was incorporating many new materials into the galleries, this was
an excellent opportunity to investigate the museum air quality. In general, the
pollutant concentrations measured in the galleries and the display cases at
Nationalmuseum are appropriate and do not warrant immediate action. During
session 2, the acetic and formic acid concentrations in galleries 3 and 4 were higher
than in session 1, possibly due to the introduction of new construction materials.
The gallery spaces may exhibit lower levels of acetic and formic acids in the future
as new construction materials off-gas. Nevertheless, it may be beneficial to monitor
for acetic and formic acid concentrations in these galleries in the future, either
using acid detecting strips, a polished lead coupon, or other air samplers. Acid
detecting strips react with organic acids and provide qualitative information about
the level of pollutants via a color change. These strips are primarily used to assess
vinegar syndrome in cellulose acetate photographic collections. If the strips trips
are used, they must remain in the dark during testing as they are light sensitive.
Lead easily corrodes in the presence of acetic acid and formic acid, and can act as a
warning dosimeter for less sensitive objects. If a lead coupon is used, care must be
taken to reduce human exposure via particulate inhalation or direct skin contact
during polishing. If acetic and formic acid concentrations in the galleries are found
to be high or are found to affect objects, action must be taken to reduce levels. This
can be done by incorporating gaseous pollutant filtration into the HVAC system,
incorporating portable air filtration devices into the gallery, or discovering the
source of the pollutant.
Similar to the gallery spaces, levels of acetic and formic acids inside the display
cases are within acceptable collection concentrations. Despite this, one concern is
that such concentrations may increase over time in the display cases containing
wooden museum objects (cases A and B). While it is certainly not uncommon to
display wooden objects inside cases, such spaces require attention if they contain
objects that are sensitive to organic acids (lead, leaded bronzes, shells, low-fire
Strategies for Pollutant Monitoring in Museum Environments 48
ceramics, limestone, tiles, cellulose, possibly some artists’ colorants). If the
sensitive objects or wooden objects cannot be moved to a different case or location,
preventive action may be required. This includes the use of pollutant filtration
media (activated charcoal, etc.), monitoring tools, and periodic visual inspection.
Another potential concern are the elevated concentrations of nitric oxide (NO)
inside the display cases containing objects at the time of measurement (cases A and
B). These display cases were also those that had a solvent-like smell when opened.
The source of NO is unclear at this time, but the cases may require further off-
gassing before closure. It may be beneficial to assess the nitrogen oxides (NOx)
concentrations inside these cases again in the future.
The procedures and measurements in this study can be easily applied to many
museums and collections. In the future, this climate monitoring experiment may act
as an example for other Swedish (and international) cultural heritage institutions
that wish to learn more about the quality of their storage and display environments.
Strategies for Pollutant Monitoring in Museum Environments 49
Disclaimer
This report contains information on various devices used for air quality monitoring
in indoor environments. The devices discussed are not representative of all
available products and services in the air quality monitoring market. The Swedish
National Heritage Board does not recommend products based on this information,
nor does it give any guarantees regarding the products’ performance and
functionality. Users of this document must perform their own research on existing
air quality monitoring tools and services. Additionally, companies can change their
available products and services at any time.
Strategies for Pollutant Monitoring in Museum Environments 50
Appendix I
Flow chart: examples of commercial air monitoring devices
Device examples are separated by their basic characteristics (sampler vs.
dosimeter, active vs. passive, direct-read vs. lab analyzed, and qualitative vs.
quantitative)
Air sampler
Active
Passive
Direct-read
Lab
analysis
Direct-read
Lab
analysis
Quantitative
€ 5 100 per
sampler, not including
pump. Often come in
packs of 10.
Gradko
International
Formaldehyde
Tube
Dräger Sampling
Tubes
Thermal
Desorption Tubes
Supelco LpDNPH
Cartridges
ORBO Sorbent
Tubes
Qualitative
40 for 250 strips
A-D Strips
Quantitative
€ 1 150 per sampler
Ozone Test Strips
Dräger Diffusion
Tubes
Gastec Passive
Dosi-Tubes
ChromAir
Chemical
Detection Badges
Safeair Chemical
Detection Badges
Dräger Bio-Check
Formaldehyde
Quantitative
€ 10 200 per
sampler
IVL Diffusve
Samplers
Gradko
International
Passive Samplers
Dräger Sampling
Tubes
Assay Technology
Badges
3M Diffusion
Monitors
Camfil Gigacheck
UMEx Passive
Samplers
Radiello Diffusive
Air Samplers
DSD-DNPH Tubes
Ultra III
VOC Check 575
Thermal
Desorption Tubes
Ogawa Sampler
Waterloo Membrane
Sampler
Quantitative
€ 5 25 per
sampler, not
including pump.
Often come in packs
of 10.
Dräger Short
Term Tubes
Strategies for Pollutant Monitoring in Museum Environments 51
Quantitative
30 per sampler
Purafil Corrosion
Classification Coupons
(CCC)
Camfil CamPure
coupons
SAAF Reactivity
Monitoring Coupons
Circul-Aire Reactivity
Monitoring Service
Metal coupons
(Ag, Cu, Pb)
Dosimeter
Passive
Lab
Analysis
Direct-read
Quantitative
> 1000 for
AirCorr/Purafil devices
Purafil OnGuard Smart
AirCorr
Metal coupons
(Ag, Cu, Pb)
Strategies for Pollutant Monitoring in Museum Environments 52
Appendix II
Table of commercial air monitoring devices
This table expands on the information presented in the flowchart of Appendix I.
The list of devices is not extensive, but does include a variety of available
techniques. “Use criteria” is designated by a number, the key for which is below:
1 No specialized deployment or interpretation skills necessary
2 No deployment skills necessary, data interpretation skills required
3 Technical skills needed for deployment, no interpretation skills necessary
4 Technical skills needed for deployment, data interpretation skills required
Although many quantitative direct-read devices are easy to interpret on site, any
device that produces quantitative results was given an ease of use value of 2, 3, or
4. This is because quantitative analysis requires knowledge about specific
pollutants and their acceptable concentrations.
Strategies for Pollutant Monitoring in Museum Environments 53
U
se
criteria
2
2
2 (includes
pump)
2
2
4
2
2
1
2
Measurement
time
1 day
- 1 month
1 - 4 weeks
several hours
10 seconds
- 8
hours
1 - 8 hours
10 seconds
- 15
minutes
15 minutes
8 hours
15 minutes
-
8 hours
1 -
3 months
Dependent on
environment
Detection
limits
< 1 ppb
< 10 µg/m
3
< 20 µg/m
3
low ppb
10 ppm
< 5 ppm
< 60 ppb
low ppb
N/A
< 1 ppb
Quantitative/
Qualitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Direct
-read/
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Direct
-read
Direct
-read
Laboratory
Laboratory
Laboratory
Direct
-read
Passive/
Active
Passive
Passive
Active
Passive/
Active
Passive
Active
Passive
Passive
Passive
Passive
Sampler/
Dosimeter
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Dosimeter
Dosimeter
Gase(s) identified
Aldehydes, CH
2O2,
CH3
COOH, NH
3, NO,
NO2, O3, SO2, VOCs
CH2O2, CH3COOH,
H2S, NH3, NO2, O3,
SO2, VOCs
CH2O
Aldehydes, CH
2O2,
CH3
COOH, VOCs
CH3
COOH, H
2S, NH3,
NO2, SO2
CH2O, CH2O2,
CH3
COOH, HCl, H
2S,
NH3, NO2
CH2O, CH3COOH, HCl,
H2S, NH3, NO2, SO2,
VOCs
CH2O, VOCs
Sulfides, Chlorides,
Oxides
Sulfides, Chlorides,
Oxides
Devices
IVL Diffusive
Samplers
Gradko International
Passive Samplers
Gradko International
Formaldehyde Tube
Dräger Sampling
Tubes
Dräger Diffusion
Tubes
Dräger Short Term
Tubes
Assay Technology
Badges
3M Diffusion Monitors
Purafil CCC
Purafil OnGuard
Smart
Strategies for Pollutant Monitoring in Museum Environments 54
Use
criteria
1
2
2
4
2
2
1
1
2
2
2
Measurement
time
1 -
3 months
1 - 30 days
15 minutes
-
7 days
15 minutes
-
30 days
Up to 7 days
1 -
48 hours
10 minutes
1 day
- 6 weeks
5 minutes
-
2 days
15 minutes
-
2 days
1 - 30 days
Detection
limits
N/A
< 1 ppb
< 50 ppb
1 ppb
< 1 ppb
< 2 ppm
< 50 ppb
low ppm
< 1 ppm
< 1 ppm
ppb
- ppt
Quantitative/
Qualitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Qualitative
Quantitative
Quantitative
Quantitative
Direct
-read/
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Direct
-read
Direct
-read
Direct
-read
Direct
-read
Direct
-read
Laboratory
Passive/
Active
Passive
Passive
Passive
Passive
Passive
Passive
Passive
Passive
Passive
Passive
Passive
Sampler/
Dosimeter
Dosimeter
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Gase(s) identified
Sulfides, Chlorides,
Oxides
CH2O2, CH3COOH, Cl2,
HCl, NH
3, NO, NO2, O3,
SO2, VOCs
Aldehydes, NH
3, NO2,
SO2
Aldehydes, H
2S, NH3,
NO2, SO2, VOCs
Aldehydes, ketones
Aldehydes, CH
2O2,
CH3
COOH, Cl
2, HCl,
H2S, NH3, NO2, SO2,
VOCs
O3
Acid gases
CH2O, Cl2, NH3, O3
CH2O, Cl2, HCl, H2S,
NH3, O3, SO2
VOCs
Devices
Camfil CamPure
Camfil Gigacheck
UMEx Passive
Samplers
Radiello Diffusive
Air Samplers
DSD-
DNPH Tubes
Gastec Passive
Dosi-Tubes
Ozone Test Strips
A-D Strips
ChromAir Chemical
Detection Badges
Safeair Chemical
Detection Badges
Ultra III
Strategies for Pollutant Monitoring in Museum Environments 55
Use
criteria
2
2 (pass.)/
4 (act.)
2
2
4
4
2
2
1
1
Measurement
time
15 minutes
- 24
hours
seconds
- 7 days
1 day
- 2 weeks
1 - 30 days
seconds
- hours
seconds
- hours
2 hours
N/A
-
dependent
on environment
1
3 months
1
3 months
Detection
limits
10 ppb
low ppb
< 1 ppb
< 1 µg/m
3
low ppb
low ppb
< 1 ppm
< 1 ppb
N/A
N/A
Quantitative/
Qualitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Quantitative
Direct
-read/
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Laboratory
Direct
-read
Direct
-read
Laboratory
Laboratory
Passive/
Active
Passive
Passive/
Active
Passive
Passive
Active
Active
Passive
Passive
Passive
Passive
Sampler/
Dosimeter
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Dosimeter
Dosimeter
Dosimeter
Gase(s) identified
VOCs
Aldehydes, CH
2O2,
CH3
COOH, H
2S, NH3,
NO2, O3, SO2 , VOCs
NH3
, NO, NO
2, O3, SO2
VOCs
Aldehydes
Aldehydes, CH
2O2,
CH3
COOH, H
2S, NH3,
NO2, O3, SO2, VOCs
Formaldehyde
Sulfides, Chlorides,
Oxides
Sulfides, Chlorides,
Oxides
Sulfides,
Chlorides,
Oxides
Devices
VOC Chek 575
Thermal Desorption
Tubes
Ogawa Sampler
Waterloo Membrane
Sampler
Supelco LpDNPH
Cartridges
ORBO Sorbent Tubes
Dräger Bio
-Check
Formaldehyde
AirCorr
SAAF Reactivity
Monitoring Coupons
Circul
-Aire Reactivity
Monitoring Service
Strategies for Pollutant Monitoring in Museum Environments 56
Appendix III
Standards for indoor air quality measurements
The following list of standards are often used in laboratories that perform indoor
air quality assessments for human health and safety studies. Such standards are not
necessary to measure or assess air quality of museum spaces with regard to
collection preservation. However, the list may be of interest to conservation
scientists with access to appropriate analytical equipment for air quality
measurements. Additionally, companies that sell laboratory analyzed air samplers
to museums may use such standards. The processes may therefore be of interest to
museum professionals collaborating with such companies.
ISO 11844-1:2006 Corrosion of Metals and Alloys -- Classification of low
corrosivity of indoor atmospheres -- Part 1: Determination and estimation of
indoor corrosivity (2006) (currently under review, will soon be replaced by
ISO/CD 11844-1). International Organization for Standards (ISO), Geneva.
ISO 9223:2012 Corrosion of Metals and Alloys -- Corrosivity of atmospheres -
- Classification, determination and estimation (2012). International
Organization for Standards (ISO), Geneva.
ISO 16000-1: 2004 Indoor Air - Part 1: General aspects of sampling strategy
(2004). International Organization for Standards (ISO), Geneva.
ISO 16000-2: 2004 Indoor Air - Part 2: Sampling strategy for formaldehyde
(2004). International Organization for Standards (ISO), Geneva.
ISO 16000-3: 2011 Indoor Air - Part 3: Determination of formaldehyde and
other carbonyl compounds in indoor air and test chamber air - Active sampling
method (2011). International Organization for Standards (ISO), Geneva.
ISO 16000-4:2011 Indoor Air -- Part 4: Determination of formaldehyde --
Diffusive sampling method (2011). International Organization for Standards
(ISO), Geneva.
ISO 16000-5:2007 Indoor Air -- Part 5: Sampling strategy for volatile organic
compounds (VOCs) (2007). International Organization for Standards (ISO),
Geneva.
ISO 16000-6:2011 Indoor Air -- Part 6: Determination of volatile organic
compounds in indoor and test chamber air by active sampling on Tenax TA
sorbent, thermal desorption and gas chromatography using MS or MS-FID
(2011). International Organization for Standards (ISO), Geneva.
ISO 16000-15:2008 Indoor Air -- Part 15: Sampling strategy for nitrogen
dioxide (NO2) (2008). International Organization for Standards (ISO), Geneva.
Strategies for Pollutant Monitoring in Museum Environments 57
ISO 16000-32:2004 Indoor Air -- Part 32: Investigation of buildings for the
occurrence of pollutants (2004). International Organization for Standards
(ISO), Geneva.
ISO 16017-1:2000 Indoor, Ambient and Workplace Air -- Sampling and
analysis of volatile organic compounds by sorbent tube/thermal
desorption/capillary gas chromatography -- Part 1: Pumped sampling (2000).
International Organization for Standards (ISO), Geneva.
ISO 16017-2:2003 Indoor, Ambient and Workplace Air -- Sampling and
analysis of volatile organic compounds by sorbent tube/thermal
desorption/capillary gas chromatography -- Part 2: Diffusive sampling (2003).
International Organization for Standards (ISO), Geneva.
Strategies for Pollutant Monitoring in Museum Environments 58
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