Mandating indoor air quality for public buildings

Abstract

If some countries lead by example, standards may increasingly become normalized

Full text

INSIGHTS
science.org SCIENCE1418 22 MARCH 2024 • VOL 383 ISSUE 6690
By Lidia Morawska, Joseph Allen, William Bahnfleth, Belinda Bennett, Philomena M. Bluyssen, Atze Boerstra, Giorgio Buonanno, Junji Cao,
Stephanie J. Dancer, Andres Floto, Francesco Franchimon, Trish Greenhalgh, Charles Haworth, Jaap Hogeling, Christina Isaxon, Jose L. Jimenez,
Amanda Kennedy, Prashant Kumar, Jarek Kurnitski, Yuguo Li, Marcel Loomans, Guy Marks, Linsey C. Marr, Livio Mazzarella, Arsen Krikor
Melikov, Shelly L. Miller, Donald K. Milton, Jason Monty, Peter V. Nielsen, Catherine Noakes, Jordan Peccia, Kimberly A. Prather, Xavier Querol,
Tunga Salthammer, Chandra Sekhar, Olli Seppänen, Shin-ichi Tanabe, Julian W. Tang, Raymond Tellier, Kwok Wai Tham, Pawel Wargocki, Aneta
Wierzbicka, Maosheng Yao
People living in urban and industrial-
ized societies, which are expanding
globally, spend more than 90% of
their time in the indoor environment,
breathing indoor air (IA). Despite de-
cades of research and advocacy, most
countries do not have legislated indoor air
quality (IAQ) performance standards for pub-
lic spaces that address concentration levels of
IA pollutants (1). Few building codes address
operation, maintenance, and retrofitting,
and most do not focus on airborne disease
transmission. But the COVID-19 pandemic
has made all levels of society, from commu-
nity members to decision-makers, realize the
importance of IAQ for human health, well-
being, productivity, and learning. We propose
that IAQ standards be mandatory for public
spaces. Although enforcement of IAQ perfor-
mance standards in homes is not possible,
homes must be designed and equipped so
that they could meet the standards.
For the past two decades, scientists have
called for national IAQ standards and laws
to be established (2), but so far, little action
has been taken. The approach to IA contrasts
sharply with outdoor air, for which qual-
ity is regulated and monitored and compli-
ance with regulations is enforced. The World
Health Organization (WHO) Global Air
Quality Guidelines (AQG) published in 2021
provide recommendations for concentration
levels of six pollutants and their averaging
times (PM2.5, PM10, NO2, SO2, CO, and O3)
and apply to both outdoor air and IA (3).
In cases for which IAQ standard and
guideline values were established by national
or association working groups, the outcomes
were inconsistent; often the criteria for the
same parameter differed by orders of magni-
tude. The reasons cited for limited progress
include different criteria in the selection of
the critical study, in the starting point, and
in the derivation procedure; the complex po-
litical, social, and legislative situation regard-
ing IAQ; the lack of an open, systematic, and
harmonized approach (4); and that establish-
ing an IAQ standard is always the result of
a compromise between scientific knowledge
and political will (5). Because of the heterog-
enous landscape of approaches needed, such
barriers remain intact despite the consider-
able IAQ research and evidence base devel-
oped over the past decades.
CHALLENGES
Source contributions
IA pollution originates from sources indoors
(including humans) and outdoors and from
chemical reactions between pollutants in IA
(6). Compliance with IAQ standards (that
refer to the concentrations of indoor pollut-
ants) would require controlling indoor emis-
sion sources (such as combustion, building
products, and cleaning products) and mini-
mizing the entry of outdoor pollutants in-
doors (for example, by filtering or treating
outdoor air to remove particles and chemical
compounds and reducing penetration of pol-
lutants through the building envelope).
During respiration, humans emit (in ad-
dition to CO2) particles that contain viruses
and bacteria. Most respiratory infections
are acquired indoors, through inhalation of
virus-laden airborne particles (7). However,
there are no exposure-response relationships
for respiratory pathogen concentrations in
IA, nor are there technologies available to
routinely monitor such pathogens in build-
ings in real time. We cannot control human
respiratory emissions in the same way that
we control emissions from other sources.
Monitoring
We cannot use the well-established ap-
proach that is used to measure outdoor
air quality to monitor IAQ. We cannot rely
on a monitoring network (in only selected
indoor public spaces) because every space
is different and is used differently, and we
cannot use modeling to predict pollution
concentration in one space by using the con-
centrations measured in other spaces. Com-
pliance monitors are too costly and complex
to deploy in all indoor spaces to monitor for
all six pollutants included in the WHO AQG
(3). However, there are environmental pa-
rameters that can already be monitored in
each room of each building, such as temper-
ature and relative humidity. The feasibility
of monitoring IAQ parameters in buildings
depends on the size, cost, robustness, and
silent operation of the sensor or monitor;
calibration; and ease of interpreting data.
But routine, real-time monitoring of indoor
pathogens is currently infeasible. In the ab-
sence of information on the concentration
of pathogens in IA, the question is which
proxy parameter or pollutant should be the
basis for legislation that targets airborne in-
fection transmission.
Legislation
Legislation comprises the system of rules—
or statutes—created and enforced by the
government of a jurisdiction. Guidelines, on
the other hand, are less formal, not manda-
tory, and generally not enforceable unless
adopted in legislation. Standards, also gener-
ally unenforceable unless they are adopted in
legislation, are typically voluntary in nature
and can set out requirements with respect
to design, operation, and performance. They
may be adopted in legislation and thus made
enforceable by law.
In terms of formal international law, there
are global treaties on transboundary air pol-
lution, but to date, no international treaty
requires or encourages adoption of ambient
air quality standards (8). It is conceptually
difficult to legislate for air quality standards
in general, let alone IAQ, because air quality
legislation is typically focused on a result or
outcome, rather than on behavior (for exam-
ple, imposing limits on pollution sources) (8).
If some countries lead by example, standards may increasingly become normalized
The list of author affiliations is provided in the
supplementary materials. Email: l.morawska@qut.edu.au
PUBLIC HEALTH
Mandating indoor air quality for public buildings
POLICY FORUM

Other challenges include the scope of what to
regulate, how monitoring and enforcement
activities are undertaken, and who has re-
sponsibility for them.
At a country level, IA legislation is ham-
pered by the tremendous variability across
jurisdictions and the particulars of each
country’s legal structure. “Air pollution”
is not defined in air quality legislation in a
substantial number of countries (8). This pre-
sents a challenge for the development of laws
on IAQ. However, the United Nations (UN)
Sustainable Development Goals provide an
opportunity for global progress on IAQ (9).
Industry priorities
Many regulations reflect compromise be-
tween the needs for human protection and
for industry opportunities, with the regula-
tory process involving balanced participa-
tion from groups with different priorities
to reach consensus. There has not yet been
sufficient coordinated support to implement
IAQ regulations. The industry most closely
related to IAQ is the heating, ventilation,
and air conditioning (HVAC) industry, which
in response to market demand has evolved
to focus primarily on thermal comfort and
energy efficiency; the market has not yet de-
manded large-scale supply of technologies
to improve IAQ. Regulation could rapidly
change this demand, which may or may not
benefit the HVAC industry and many other
building industries. There will always be
some industries that do not benefit and/or
will require strategic change owing to new
regulations, so they would prefer the status
quo. There are groups who will be forced
into capital costs by regulation change (such
as property owners and their associations)
that must be convinced of need and value.
Thus, in the pursuit of new IAQ regulation,
market forces may mean that industry sup-
port is not guaranteed.
The social and political dimension
Introducing standards is complex, not only
because scientific parameters may be con-
tested or technically difficult to achieve
but also because human stakeholders have
different values, goals, and power, and
standards may have cultural or political
implications. A particular standard may be
unfeasible in any given setting (for exam-
ple, because it is unaffordable or blocked
by powerful individuals or groups), so
compromises must be made. Organizations
that choose (or are required) to implement
standards must go through a complex and
sometimes costly process to identify, as-
similate, implement, and adapt them.
ADDRESSING THE CHALLENGES
The proposed approach is based on science,
technology, and specific solutions that have
existed for some time and can now serve as
a basis for addressing a complex interdisci-
plinary problem.
Pollutants recommended by WHO
Low-cost sensors are a viable technology to
measure some of the six pollutants included
in the WHO AQG; however, not all six can
be realistically monitored in buildings, nor
do they all need to be monitored. The two
most relevant candidates for routine regula-
tory IAQ monitoring are PM2.5 and CO, for
which low-cost advanced sensors have dem-
onstrated stability, durability, and robust-
ness. Particulate matter in IA originates from
indoor and outdoor sources, and exposure
to PM2.5 is among the 10 leading risks (10).
CO arising from various natural processes is
present in the atmosphere at very low con-
centrations, but it is incomplete combustion
(indoor and outdoor) that can raise concen-
trations to levels harmful to humans. Indoor
CO should be routinely measured in areas
where outdoor CO concentrations exceed
regulations and where indoor combustion
takes place. In several countries, CO monitors
are mandated in spaces where combustion
takes place to alert to life-threatening levels
of gas, but these monitors are typically not
sufficiently sensitive to lower concentrations.
Carbon dioxide
Currently CO2 concentration values are
not included in the WHO AQG. However,
regardless of the potential harm it causes,
CO2 can serve as a proxy for occupant-emit-
ted contaminants and pathogens and as a
means to assess the ventilation rate. CO2
sensors are readily available, inexpensive,
and robust and can be used in all interiors.
The advantage of using CO2 as a proxy is
that although both pathogens and CO2 are
emitted during human respiratory activi-
ties, it is much easier to link CO2 concentra-
tions to these activities than to model risk
from the emissions of pathogens.
Ventilation
Ventilation with clean air is a key control
strategy for contaminants generated indoors.
The efficacy of ventilation in reducing infec-
tion risk has been demonstrated in many
studies (11). The role of ventilation is to re-
move and dilute human respiratory effluents
and body odors and other indoor-generated
pollutants at a rate high enough relative to
their production so that they do not accu-
mulate in IA. IA is replaced (diluted) with
outdoor air (assumed to be clean) or clean
recirculated air. Outdoor air ventilation rates
are almost always set according to criteria
of hygiene and comfort (perceived air qual-
ity). Effective air distribution (ventilated
air reaching the entire occupied zone and
airflow not directed from one person to an-
other) is a practical candidate for a standard.
The measured ventilation rate can be used as
a proxy of IAQ.
Although technologies for measuring ven-
tilation already exist in most modern me-
chanically ventilated buildings, monitoring
the ventilation rate in terms of clean air de-
livered to the space without considering the
number of occupants or their activities is not
sufficient to ensure adequate IAQ. One way
to assess the quality of ventilation is to con-
currently measure the CO2 concentration: If
it rises above an accepted threshold relative
to the outside concentration or concentra-
tion in the recirculated air brought into the
room, the ventilation is inadequate.
Suggested numerical levels
Below, we provide justification for proposed
numerical levels and their averaging times
for the pollutants and the parameters dis-
cussed above (see the table). Actual levels
adopted by countries and jurisdictions will
differ, reflecting local circumstances and
competing priorities.
PM2.5 concentration. It is proposed that the
WHO AQG 24 hours, 15 µg/m3 level be consid-
ered as the basis for IAQ standards, but with
a 1-hour averaging time because 24 hours is
much longer than people typically spend in
public places or, for that matter, that public
spaces are occupied. This is a compromise
between the realistic occupancy of and expo-
sure in public spaces and the need for rigor
in the derivation of the health-based value.
SCIENCE science.org 22 MARCH 2024 • VOL 383 ISSUE 6690 1419
LEVEL
AVERAGING
TIME OR SETPOINT
PM2.5, μg/m 315(i) 1-hour
CO2, ppm 800
(absolute
value)(ii)
threshold
350(delta)(iii) threshold
CO , mg /m3100(iv) 15 minutes(iv)
35(iv) 1 hour(iv)
10(iv) 8 hours(iv)
Ventilation,
liters/s
per person
14(v) When the
space
is occupied
Proposed parameter levels
Values may be adjusted to reflect local
circumstances and priorities.
PUBLIC HEALTH
Mandating indoor air quality for public buildings
(i) 24-hour level from (3). (ii) When 100% of air delivered to the
space is outdoor air, assuming outdoor CO2 concentration is
450 ppm; based on classroom scenario (see SM). (iii) Delta is
the difference between the actual CO concentration and the
CO2 concentration in the supply air. (iv) 8-hour averaging time,
from (15). (v) Clean air supply rate in the breathing zone; see
(12). At 25°C and 1 atm for CO 1 ppb = 1.15 g/m3. Threshold is
the concentration level of CO2 that must not be exceeded.

1420 22 MARCH 2024 • VOL 383 ISSUE 6690 science.org SCIENCE
Using the WHO AQG value for 24-hour ex-
posure for 1-hour exposure is a conservative
approach that considers each environment
as though it were the only one where people
spend all their time.
CO2 concentration. To decide on a level that
would adequately control the risk of infec-
tion in public spaces, a scenario of exposure
must be defined and then a risk assessment
model be applied. We propose a scenario of
a classroom with one infected student [see
supplementary materials (SM)]. A ventila-
tion rate of 14 liter/s per person, keeping
CO2 concentrations at or below the standard
level proposed in the table, would ensure
that the reproduction number Re < 1 even
for respiratory pathogens with high trans-
missibility, such as severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) Delta
and Omicron variants and measles. The rec-
ommended level of 800 parts per million is
within an already relatively narrow range of
values of the CO2 levels recommended by dif-
ferent organizations and countries (see SM).
This approach takes outdoor concentration
as a baseline. However, not only are outdoor
concentrations continually increasing be-
cause of emissions to the atmosphere that
outweigh removal, which must be taken into
account in the formation of the standard,
there are also variations between locations,
and at individual locations there are diurnal
and annual variations. Therefore, jurisdic-
tions should consider local CO2 baseline lev-
els when setting levels.
In indoor environments where the sup-
plied ventilation air is a mixture of outdoor
air and recirculated air, the CO2 concentra-
tion can be high, but the risk of infection
may be low provided that the supplied ven-
tilation air is sufficient. This is because the
recirculated air is often filtered, and most of
the pathogens are removed before it reenters
the space; however, gaseous pollutants, such
as CO2, are not removed by this process. The
actual (absolute) CO2 concentration in the
space and the difference between the actual
CO2 concentration and the CO2 concentra-
tion in the air delivered to the space (out-
door air delivered with natural ventilation or
air delivered by mechanical ventilation sys-
tems) are assumed as a proxy for ventilation.
Ventilation rate. The recommended rate of 14
liters/s per person, based on (12), is higher
than the WHO-recommended minimum
ventilation rate for nonresidential settings of
10 liters/s per person (3), or the highest cate-
gory I ventilation rate defined in the existing
standard ISO 17772-1. However, it is in line
with ventilation rate recommended by (11),
based on an experimental exposure study of
a cohort of school children.
Legislation
As noted in the UN-EP 2021 report, one ad-
vantage of an IAQ regulatory framework is
the ability to place obligations on owners of
indoor premises (8). This contrasts with am-
bient air quality, which generally relates to
“unowned” air for which allocating responsi-
bility can be more difficult (2). Premises that
operate under extant legal frameworks (such
as workplaces, schools, and hospitals) may be
more amenable to regulatory control through
these frameworks (2) to consider as part of
the development of laws for IAQ (table S2).
IMPLEMENTATION OF STANDARDS
For IAQ standards to have practical value,
they must be implementable; buildings must
be designed, constructed, maintained, oper-
ated, or retrofitted to meet the standards,
given the intended use, and must be used ac-
cordingly. This should be checked at delivery
and routinely throughout the building life.
Standards must establish specifications for
IAQ and be technically feasible, affordable
to construct and operate, and compatible
with other priorities and constraints such as
energy use. Several means are available for
achieving IAQ that meets these objectives.
The use of natural or hybrid ventilation
(natural ventilation supplemented by me-
chanical ventilation when necessary) when
feasible can greatly reduce space condition-
ing energy requirements and associated oper-
ating costs. Stratified air supply (distributing
air to create vertical stratification of tempera-
ture and contaminant concentrations) by us-
ing displacement ventilation or underfloor
air supply and personal ventilation (supply
of clean air directly to the breathing zone of
each occupant) can have a positive impact.
For required delivery of outdoor air, high-ef-
ficiency air-to-air energy recovery is essential
and required by many energy standards.
Additional measures in support of ventila-
tion, such as air cleaning and disinfection,
can greatly reduce the need to increase out-
door air supply, which carries a substantial
energy penalty. Filtration of recirculated air
is an effective way to reduce concentration
of, and exposure to, airborne particulate
matter, allergens, and pathogens. Other air
treatment technologies may help inactivate
infectious airborne particles. Work is ongoing
to develop consensus methods for determin-
ing the effectiveness of some of these tech-
nologies and safety measures.
The use of demand control (modulating
control levels in response to need and acti-
vation of higher levels of protection) can be
guided by public health data, for example,
during annual influenza seasons or when a
new pathogen emerges with the potential to
cause an epidemic. The recently published
ASHRAE Standard 241–2023 Control of In-
fectious Aerosols (13) incorporates most of
the noted measures and is intended to apply
during periods of elevated risk of airborne
disease transmission.
Actions to address IAQ will add cost in
the short term and may not be prioritized by
many countries because of pressures on bud-
gets. However, if some countries lead by ex-
ample, we anticipate that IAQ standards will
increasingly become normalized. Social and
economic benefits in terms of public health,
well-being, and productivity and perfor-
mance will likely far outweigh the investment
costs in achieving clean IA. Few countries
realize the enormity of public health costs,
but disability-adjusted life years (DALYs) at-
tributable to IA pollution accounted for an
estimated 14.1% of the total DALYs in China
for the period from 2000 to 2017, and corre-
sponding financial costs (not including the
costs of IA-borne infection transmission) ac-
counted for 3.45% of China’s gross domestic
product (14). By making IAQ standards the
reality, we will improve our health and well-
being, and also save money. j
REFERENCES AND NOTES
1. L. Morawska, W. Huang, in Handbook of Indoor Air Quality,
Y. Zhang, P. Hopke, C. Mandin, Eds. (Springer, 2022), pp.
1–20.
2. R. Corsi, EM Pittsburgh-Air and Waste Management
Association, pp. 10–15 (2000).
3. WHO, “WHO global air quality guidelines: Particulate
matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur
dioxide and carbon monoxide” (WHO, 2021).
4. L. Morawska, Proceedings of the Healthy Buildings
Conference, Espoo, Finland, 6 to 10 August 2000 (Curran,
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5. T. Salthammer, Chemosphere 82, 1507 (2011).
6. C . J. Wesch ler, Indoor Air 21, 205 (2011).
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8. UN Environmental Program (UN-EP), “Regulating air
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Health 10.3389/fpubh.2022.1087087 (2022).
12. J. G. Allen et al., “Proposed non-infectious air delivery
rates (NADR) for reducing exposure to airborne
respiratory infectious diseases” (The Lancet COVID-19
Commission, 2022).
13. ASHRAE, ASHRAE standard 241-2023. Control of infec-
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14. N. Liu et al., Lancet Planet. Health 7, e900 (2023).
15. WHO, “Guidelines for indoor air quality, selected pollut-
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ACKNOWLEDGMENTS
This paper was supported by the Australian Research
Council (ARC) Industrial Transformation Training
Centre (IC220100012) and ARC Laureate Fellowship
(FL220100082). The Engineering and Physical Sciences
Research Council (EPSRC) funded the CO-TRACE project
(grant EP/W001411/1), UK Research and Innovation [EPSRC,
Natural Environment Research Council (NERC), Australian
Human Rights Commission (AHRC)] funded the RECLAIM
Network Plus project (grant EP/W034034/1), and NERC
funded the GreenCities project (grant NE/X002799/1).
SUPPLEMENTARY MATERIALS
science.org/doi/10.1126/science.adl0677
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