No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of an ozone-generating air purifier on indoor secondary particles in three residential dwellings
Indoor Air
Abstract
Unlabelled:
The use of indoor ozone generators as air purifiers has steadily increased over the past decade. Many ozone generators are marketed to consumers for their ability to eliminate odors and microbial agents and to improve health. In addition to the harmful effects of ozone, recent studies have shown that heterogeneous and homogeneous reactions between ozone and some unsaturated hydrocarbons can be an important source of indoor secondary pollutants, including free radicals, carbonyls, carboxylic acids, and fine particles. Experiments were conducted in one apartment and two detached single-family dwellings in Austin, TX, to assess the effects of an ozone generator on indoor secondary organic aerosol concentrations in actual residential settings. Ozone was generated using a commercial ozone generator marketed as an air purifier, and particle measurements were recorded before, during, and after the release of terpenes from a pine oil-based cleaning product. Particle number concentration, ozone concentration, and air exchange rate were measured during each experiment. Particle number and mass concentrations increased when both terpenes and ozone were present at elevated levels. Experimental results indicate that ozone generators in the presence of terpene sources facilitate the growth of indoor fine particles in residential indoor atmospheres. Human exposure to secondary organic particles can be reduced by minimizing the intentional release of ozone, particularly in the presence of terpene sources.
Practical implications:
Past studies have shown that ozone-initiated indoor chemistry can lead to elevated concentrations of fine particulate matter, but have generally been completed in controlled laboratory environments and office buildings. We explored the effects of an explicit ozone generator marketed as an air purifier on the formation of secondary organic aerosol mass in actual residential indoor settings. Results indicate significant increases in number and mass concentrations for particles <0.7 microns in diameter, particularly when an ozone generator is used in the presence of a terpene source such as a pine oil-based cleaner. These results add evidence to the potentially harmful effects of ozone generation in residential environments.
... Furthermore, our results showed that in the non-controlled environment, without the HEPA filter, ozone reacted with the particles therein promoting a substantial decrease in 5 μm particles. However, due to their fragmentation, a significant increase in the number of 0.5 μm particles was observed 25,26 ...
... The results of their study suggest that the occupants of residential dwellings may also be exposed to elevated levels of fine and ultra-fine particles when an ozone generator is employed in a residential setting, particularly during periods of relatively high terpene concentrations, e.g., during the use of pine oil-based cleaners or scented deodorizers, what should be a concern with respect to elevated inhalation exposure. 26 Ozone's reaction with several compounds occurs in two different ways and both coexist. One involves direct reac-tions of molecular ozone and the other occurs through reactions of its subproducts, such as free radicals. ...
... The formation and effect of these secondary organic particles in human health need to be clarified. 12,26 In contrast, in the controlled room, this increase in 0.5 μm particles was not observed as these particles were almost eliminated when ozone was applied in a room with a HEPA filtering system. These data suggest that the particles cleaved by ozone were effectively filtered from the environment by the HEPA filter because a significant reduction in the total particle count (0.5 μm and 5 μm) was observed when compared with the counts obtained before ozonation, just with the HEPA filter. ...
Objective Airborne particles are one of the most important factors in the spread of infectious pathogens and must be monitored in healthcare facilities. Viable particles are living microorganisms, whereas non-viable particles do not contain microorganisms but act as transport for viable particles. The effectiveness of ozone in reducing these particles in a non-controlled room and a controlled cleanroom using high-efficiency particles air (HEPA) filter was analyzed in this study.
Materials and Methods Viable particles and non-viable particles sized 0.5 and 5 μm were quantified before and after ozonation in two different health environments: non-controlled (group 1) and controlled area, which was associated with a HEPA filtering system (group 2). Active air sampling using a MAS 100 was used to count the number of viable particles, while the number of non-viable particles/m3 was obtained following the manufacturer's recommendations of the Lasair III 310C system.
Results Our results of the viable particles counting were not quantifiable and analyzed using statistical tests. Both groups showed a slight tendency to reduce the number of viable particles after ozonation of the environmental air. A statistically significant reduction of non-viable 5 μm particles after ozonation was observed in both groups (G1: p = 0,009; G2: p = 0,002). Reduction in the non-viable 0.5 μm particles after ozonation was observed only in group 2, associated with the HEPA filter. In group 1, after ozonation, a significant increase in 0.5 μm particles was observed, probably due to the breaking of 5 μm particles by ozone gas. Our results suggest that ozone gas can break 5 μm particles and, when associated with a HEPA filter, increases its effectiveness in removing 0.5 μm particles.
Conclusion Considering that 5 μm particles are important in the air transport of microorganisms, their reduction in the environment can be a relevant parameter in controlling the dissemination of infections.
... Pollutant sources and emission rates may rapidly change over time (Luengas et al. 2015). Indoor pollutant sources include permanent sources (building materials, carpets, paints, varnishes, etc.) and occasional sources (furniture, cleaning and disinfection products, cooking, personal care products, tobacco smoke etc.), while outdoor pollutants intrusion mostly depends on human activities (road traffic, industry, etc.) (Hubbard et al. 2005). Table 1 summarizes the most relevant indoor air pollutants, their typical sources and commonly used measurement methods. ...
... On the other hand, electrical filtration attracts and retains negatively charged particles on a plate of opposite polarity. Unfortunately, by-products such as ions, ozone or other compounds may be generated during electronic Occupants producing CO 2 as well as fireplaces and some cooking and heating devices Radon Radon is a radioactive gas that is released through the decay of radium in soils and rocks and enters indoor air spaces of buildings or other enclosed locations Real-time devices using alpha-particle sensitive material a WHO (2010WHO ( , 2015, Rösch et al. (2014) b International WELL Building Institute (2019) filtration (Luengas et al. 2015;Hubbard et al. 2005). Adsorption involved the retaining of pollutants on a surface and happens because all molecules employ attractive forces, especially molecules at the exterior of solid materials with a large surface area (e.g. ...
... In addition, health issues may arise from potentially toxic indoor levels of O 3, which has a typical exposure limit of only 0.1 ppm v for 8 h (Luengas et al. 2015;Hubbard et al. 2005;Chen et al. 2005). This paper presents the recent research findings on biological indoor air purification methods as a 'green' alternative to physical-chemical methods for improving indoor air quality, with emphasis on the recent advances, current challenges, and opportunities for further development. ...
Studies on human exposure to indoor air pollution reveal that indoor environments could be at least twice as polluted as outdoor environments. Indoor air pollution has not received as much attention than outdoor air pollution, despite an adult spending now most of the time indoors as a result of the global shift in the economy from the manufacturing sector towards the service and knowledge-based sectors, which operate in indoor office environments. Additionally, the health threats caused by a long-term exposure to indoor air pollution have become more apparent over the last decades as buildings are progressively sealed against the outside climate conditions to obtain heating and cooling energy cost savings and in response to stricter safety guidelines. Currently there is not a single technology that can efficiently provide a complete and satisfactory purification of indoor air. Biological systems for improving indoor air quality are promising, but challenges need to be examined to properly address the bioavailability of low pollutant concentrations, guarantee microbial safety, and incorporate CO2-removal. This study presents the recent research advances in biological indoor air purification methods as a ‘green’ alternative to physical–chemical methods, with emphasis on current challenges and opportunities it can provide for improving Indoor Environment Quality, building energy cost savings and improvements on indoor comfort and well-being.
Graphical abstract
... Moreover, pollutant sources and emission rates rapidly change over time (Luengas et al., 2015): endogenous sources include permanent (building materials, adhesives, paints, varnishes, etc.) and occasional sources (furniture, cleaning and disinfection products, cooking, personal care products, human metabolism, etc.), while outdoor pollutants intrusion clearly depends on human activities (road traffic, industry, etc.). Additionally, secondary pollutants might be produced by indoor gas-phase reactions from other compounds present in indoor air (Hubbard et al., 2005;SCHER, 2007). ...
... While acute exposure to high concentration can produce irritation and inflammation, no chronic exposure risks have been reported yet. Health risks might be expected when ozone or other reactive radicals are present, due to their high reactivity with pinene and other unsaturated molecules (Hubbard et al., 2005;Kotzias et al., 2005;Leung, 2015;SCHER, 2007). These reaction byproducts would produce eye and upper airways irritation in a more extended way than pinene itself. ...
... Chronic health effects for limonene have not been studied, and there is no evidence of carcinogenicity or genotoxicity. Heath risks are associated to ambient reaction with ozone or reactive radicals, which form byproducts such as aldehydes, carboxylic acids and peroxides, responsible of irritation and odor annoyance at low concentrations (Hubbard et al., 2005;Kotzias et al., 2005;Leung, 2015;SCHER, 2007). Maximum concentrations of 32, 19 and 11 mg/m 3 have been recorded at homes, offices and schools, respectively (Dodson et al., 2008;Du et al., 2015;Edwards et al., 2001;Geiss et al., 2011;Langer et al., 2015;Mandin et al., 2017;R€ osch et al., 2014;Xu et al., 2016;Zhong et al., 2017). ...
Indoor air pollution has traditionally received less attention than outdoors pollution despite indoors pollutant levels are typically twice higher, and people spend 80–90% of their life in increasing air-tight buildings. More than 5 million people die every year prematurely from illnesses attributable to poor indoor air quality, which also causes multi-millionaire losses due to reduced employee’s productivity, material damages and increased health system expenses. Indoor air pollutants include particulate matter, biological pollutants and over 400 different chemical organic and inorganic compounds, whose concentrations are governed by several outdoor and indoor factors. Prevention of pollutant is not always technically feasible, so the implementation of cost-effective active abatement units is required. Up to date no single physical-chemical technology is capable of coping with all indoor air pollutants in a cost-effective manner. This problem requires the use of sequential technology configurations at the expenses of superior capital and operating costs. In addition, the performance of conventional physical-chemical technologies is still limited by the low concentrations, the diversity and the variability of pollutants in indoor environments. In this context, biotechnologies have emerged as a cost-effective and sustainable platform capable of coping with these limitations based on the biocatalytic action of plants, bacteria, fungi and microalgae. Indeed, biological-based purification systems can improve the energy efficiency of buildings, while providing additional aesthetic and psychological benefits. This review critically assessed the state-of-the-art of the indoor air pollution problem and prevention strategies, along with the recent advances in physical-chemical and biological technologies for indoor pollutants abatement.
... Volatile organic compounds (VOCs), which mainly contain alkanes, aromatics, alkenes, carboxylic acids, esters and alcohols [1], have been proven to seriously damaged environment and human health owning to their toxic carcinogenesis and environmental destructiveness such as photochemical smog, greenhouse effect and stratospheric ozone depletion. To solve this problem, several effective VOC elimination techniques such as adsorption [2], ozonation [3], chemical combustion [4], biological degradation [5] and photocatalytic oxidation [6][7][8] have been proposed in recent decades. Among the above methods, photocatalytic oxidation technology is a promising method for removing gaseous pollutants with a low concentration, owing to its excellent features of operation at room temperature and high activity towards various pollutants which can react to final products (CO 2 and H 2 O) [9][10][11]. ...
... Defects in tungsten oxide materials can exhibit strong adsorption capability towards VOCs [42][43][44][45]. Wang et al. [46] reported oxygen vacancies can act as active sites on the VOC degradation of WO 3 . The results showed that oxygen vacancies from WO 3−x can capture oxygen atoms from the formaldehyde and H 2 O, which boost the production of hydroxyl radicals and lead to the oxidization and degradation of formaldehyde and benzene. ...
... This rabbit craft sample doped Fe (the content is 4.56%) showed a 98.21% degradation rate of formaldehyde in 6 h. The detailed photocatalytic reaction mechanism of HCHO was also proposed in Fig. 4: Fe 3+ as a scavenger can not only trap the Fig. 4 Mechanism of photocatalytic degradation of HCHO by wood covered with Fe-doped WO 3 . Reproduced with permission from Ref. [68] Copyright 2016 Elsevier electrons and holes of WO 3 to prevent the recombination of excited charge carriers, but also participate in the oxidation reactions with hydroxyl ions and oxygen to form hydroxyl radicals and superoxide radicals, and then these energetic free radicals attack formaldehyde to form the final product such as CO 2 and H 2 O. Irie et al. [69] also did the similar work through doped Cu(II) into the interior structure of WO 3 , which exhibits 16 times higher photocatalytic ability for 2-propanol decomposition than that of N-doped TiO 2 . ...
Photocatalytic oxidation process for the degradation of volatile organic compounds (VOCs) contaminants is a promising technology. But until now, the low photocatalytic activity of the conventional TiO2 photocatalyst under visible-light irradiation hinders the deployment of this technique for VOCs degradation. WO3 has been proved to be a suitable photocatalytic material for degradation of various VOCs as its appropriate band-gap, high stability and great capability. Nevertheless, the actual implementation of WO3 is still restricted by short lifetime of photoexcited charge carriers and low light energy conversion efficiency: its photocatalytic performance is needed to be improved. This review discusses the process of tungsten-based photocatalyst for removal of VOCs and summarizes a variety of strategies to improve the VOCs oxidation performances of WO3, such as controlling the morphology structure, engendering chemical defects, coupling heterojunction, doping suitable dopants and loading a co-catalyst. In addition, the practical application of tungsten-based photocatalyst is discussed.
... 27 Several types of air puriers can increase indoor O 3 levels, either deliberately (e.g., O 3 generators) or as a byproduct of their operation (e.g., ion generators, electrostatic precipitators, and some UV-lamp containing air cleaners). [28][29][30] Specic devices may emit oxidants other than O 3 . 31 Most emission sources are constrained only to select chemicals (e.g. ...
... The reduction of O 3 levels during use of a gas stove has been attributed to titration by NO (R3). 29 Ozone Photochemistry outdoors generates O 3 , a major component of photochemical smog. Levels of 10s to 100s of ppbv of O 3 are common in polluted outdoor environments. ...
... As described above, high NO levels titrate O 3 from indoor environments through reaction (R3). 29 ...
The chemistry of oxidants and their precursors (oxidants*) plays a central role in outdoor environments but its importance in indoor air remains poorly understood. Ozone (O3) chemistry is important in some indoor environments and, until recently, ozone was thought to be the dominant oxidant indoors. There is now evidence that formation of the hydroxyl radical by photolysis of nitrous acid (HONO) and formaldehyde (HCHO) may be important indoors. In the past few years, high time-resolution measurements of oxidants* indoors have become more common and the importance of event-based release of oxidants* during activities such as cleaning has been proposed. Here we review the current understanding of oxidants* indoors, including drivers of the formation and loss of oxidants*, levels of oxidants* in indoor environments, and important directions for future research.
... Ozone generators use UV radiation or a corona discharge to produce O 3 from oxygen to eliminate microbial agents and odours (Hubbard et al., 2005). However, O 3 concentrations that do not exceed typical exposure limits (50-100 ppb) cannot guarantee efficient removal of indoor air contaminants (Chen et al., 2005;Hubbard et al., 2005), and moreover reactions with terpenes can produce potentially harmful secondary organic aerosol, carbonyls, carboxylic acids and free radicals (Waring et al., 2008). ...
... Ozone generators use UV radiation or a corona discharge to produce O 3 from oxygen to eliminate microbial agents and odours (Hubbard et al., 2005). However, O 3 concentrations that do not exceed typical exposure limits (50-100 ppb) cannot guarantee efficient removal of indoor air contaminants (Chen et al., 2005;Hubbard et al., 2005), and moreover reactions with terpenes can produce potentially harmful secondary organic aerosol, carbonyls, carboxylic acids and free radicals (Waring et al., 2008). For these reasons, O 3 generators are not recommended by public health agencies as a safe and effective way to control indoor air pollutants (EPA, 2014). ...
In today's ‘indoor generation’ most human activities take place within an enclosed space, characterised by a chemically diverse and complex air quality. Although source control is the universally preferred approach to reduce contaminants, this is becoming increasingly insufficient, technically unfeasible or economically unviable. The provision of adequate ventilation is also being challenged by invariably poor outdoor air quality and our quest for a low carbon economy. Whilst the former directly adds to the burden of indoor air pollution, both factors attract mitigation measures that are leading to efforts to seal off indoor spaces, which can increase exposure to endogenous indoor air pollutants, heighten health risks and curtail concentration, learning and productivity. Research to date on the role of air purification technologies in key indoor microenvironments demonstrates that air filtration produces clear reductions in indoor pollution concentrations. To confirm the optimistic modelled health/performance benefits associated with air purification further research is required, evaluating longer term interventions particularly in vulnerable populations, employing real-time sensors to quantitatively assess complete exposure profiles and optimizing technologies/strategies to remove specific indoor air pollutants (eg infiltrated versus endogenous particles, gases, chemically transformed organics) within the unique spaces where people live, learn, work and travel.
... Siegel (2016) pointed out that a device intended as an air cleaner that intentionally emits any compound into indoor air should not be considered a true air cleaner because the contamination can outweigh any air cleaning benefits. A study by Hubbard et al. (2005) focused on ozone generators as air purifiers. The authors measured peak concentrations of ozone of between 55 μg/m 3 and 102 μg/m 3 in different types of dwellings during the operation of such devices. ...
... Waring et al. (2008) studied portable air cleaners in a 14.75 m 3 stainless steel chamber and measured ozone emission rates of between 3.3 mg/h and 4.3 mg/h per unit. To estimate ozone indoor concentrations based on emission rates, Hubbard et al. (2005) use Eq. (3), which assumes steady-state conditions in a well-mixed environment in the absence of outdoor ozone and significant indoor chemistry. ...
Background:
Although it is recognized that ozone causes acute and chronic health effects and that even trace amounts of ozone are potentially deleterious to human health, information about global and local exposures to ozone in different indoor environments is limited. To synthesize the existing knowledge, this review analyzes the magnitude of and the trends in global and local exposure to ozone in schools and offices and the factors controlling the exposures.
Methods:
In conducting the literature review, Web of Science, SCOPUS, Google Scholar, and PubMed were searched using 38 search terms and their combinations to identify manuscripts, reports, and directives published between 1973 and 2018. The search was then extended to the reference lists of relevant articles.
Results:
The calculated median concentration of ozone both in school (8.50 μg/m3) and office (9.04 μg/m3) settings was well below the WHO guideline value of 100 μg/m3 as a maximum 8 h mean concentration. However, a large range of average concentrations of ozone was reported, from 0.8-114 μg/m3 and from 0 to 96.8 μg/m3 for school and office environments, respectively, indicating situations where the WHO values are exceeded. Outdoor ozone penetrating into the indoor environment is the main source of indoor ozone, with median I/O ratios of 0.21 and 0.29 in school and office environments, respectively. The absence of major indoor ozone sources and ozone sinks, including gas-phase reactions and deposition, are the reasons for lower indoor than outdoor ozone concentrations. However, there are indoor sources of ozone that are of significance in certain indoor environments, including printers, photocopiers, and many other devices and appliances designed for indoor use (e.g., air cleaners), that release ozone either intentionally or unintentionally. Due to significantly elevated outdoor ozone concentrations during summer, summer indoor concentrations are typically elevated. In addition, the age of a building and various housing aspects (carpeting, air conditioning, window fans, and window openings) have been significantly associated with indoor ozone levels.
Conclusions:
The existing means for reducing ozone and ozone reaction products in school and office settings are as follows: 1) reduce penetration of outdoor ozone indoors by filtering ozone from the supply air; 2) limit the use of printers, photocopiers, and other devices and appliances that emit ozone indoors; 3) limit gas-phase reactions by limiting the use of materials and products (e.g. cleaning chemicals) the emissions of which react with ozone.
... Sheu et al. (2020) studied the third-hand smoke in smokeless cinemas and identified 2,5dimethylfuran, acrolein, 2-methylfuran, furfural, furfuryl alcohol, phenol, benzaldehyde, benzene, and toluene in the air [29]. These compounds have also been reported in other studies on third-hand smoke [8,21,24,30]. Although the concentrations of third-hand smoke substances in the air are significantly lower than those in second-hand smoke, they can persist for extended periods. ...
Tobacco smoke is an important pollutant that causes over 8 million deaths each year, of which, 1.3 million deaths are attributed to second-hand smoke. Third-hand smoke refers to the chemical emitted from smoking that remains in the air, dust, and on the surfaces after smoking has stopped. These substances, which are deposited or adsorbed on indoor surfaces and dust and can be re-emitted into the indoor air continually, leading to human exposure over an extended period. The properties of the third-hand smoke chemicals and indoor surfaces are key factors influencing their indoor behaviors and human exposure. Additionally, the substances on surfaces can react with atmospheric oxidants to form secondary pollutants. For instance, nicotine in third-hand smoke reacts with atmospheric oxidants (ozone, nitrous acid, and hydroxyl radicals) to produce other toxic, carcinogenic substances, which may be more toxic, further increasing the risk to human health. This review aims to address three key questions: (1) What are the components of third-hand smoke? (2) How does third-hand smoke adsorb and desorb on/from indoor surfaces, and undergo chemical transformation? (3) How is exposure to third-hand smoke related to human health effects? Therefore, we conducted a comprehensive review of the chemical composition of third-hand smoke, its adsorption and desorption on indoor surfaces, chemical transformations indoors, and health effects, The chemical composition of third-hand smoke is complex, containing various toxic substances, carcinogens, and heavy metals. This review provided suggestions to prevent exposure to third-hand smoke.
... It has been reported for both textile and non-textile applications. Air purification techniques utilize this gas, 22 wastewater can be treated by it, 23 while in agriculture sector, soil remediation is carried out by this gas. 24 It is also utilized for cleaning of surfaces 25 and disinfections. ...
Most effective and durable finishes for cotton fabrics typically contain toxic and sometimes carcinogenic chemicals. Although certain bio-based alternative finishes have been reported in literature but these alternatives are usually less effective than conventional toxic finishes. To improve the performance of bio-based finishes, this paper develops and improves a novel and ecofriendly finishing process for 100% cotton fabric, based on ozone treatments in very controlled amount for the first time. Four types of bio-finishes including citric acid, stearic acid, diammonium hydrogen phosphate and fatty acid amide, for easy care, water repellency, fire retardancy and softness properties respectively were used in this research. For each finish, three ozone-based finishing processes; pre-ozonation, in-situ ozonation, and post-ozonation were developed and optimized. For all four types of bio finishes, fabrics with 20% post ozonation exhibited superior finish performance. Crease recovery angle increased from 121° to 194°, water repellency rating improved from rating 0 to 90, char length decreased from 26.6 cm to 10.8 cm and bending length decreased from 2.16 mm to 1.1 mm by using bio-based finishes with ozone exposure without compromising mechanical and comfort properties of cotton fabrics. SEM, FTIR and XRD analysis were also performed on ozone exposed and finished fabrics.
... 20,38-42 Indeed, it has been shown that the deposited aerosol dose in the particle range of 1.2-800 nm, formed by the ozonolysis of monoterpenes during the mopping event is greater than, or comparable to, that one would inhale in an urban street canyon traffic. 1,43,44 In the present investigation, we conducted a real-time assessment of aerosol particle formation following the reaction between gaseous ozone (O 3 ) and a commonly utilized oorcleaning detergent. This study was designed to simulate indoor environmental conditions, examining scenarios both devoid of light and exposed to UV-light within the range typical for indoor settings (320 nm < l < 400 nm). ...
Cleaning detergents are a source of numerous volatile organic compounds (VOCs) which are highly reactive towards ozone leading to the formation of secondary organic aerosols (SOA) in indoor environments. Here we perform real-time measurements of the organic composition of aerosols produced upon ozone reaction with floor cleaning detergent by extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) coupled to a chamber reactor. The experiments were performed in the absence of light and under light irradiation (320 nm < λ < 400 nm) simulating the fraction of sunlight that penetrates indoors. The multiple increases in particle number concentrations correspond to rise in the signal intensity of specific species. Notably, the secondary increase in particle mass concentration is mainly contributed by highly oxidized molecules (HOMs), which increased from 16.5% upon ozone oxidation to 19.9% under photo-oxidation reactions. A large fraction of CHON compounds such as imidazole, pyrazine/pyrimidine, and azaindole was observed most likely formed through the reaction of O3 with benzothiazole (constituent of the cleaning detergent). The difference between the molecular compositions detected in the absence of light and in the presence of light indicates that sunlight penetrating through the windows can affect the SOA produced by the reaction of ozone with the floor cleaning detergent.
... "Air purifiers" with ionizers are to be classified as problematic, as they can lead to ozone pollution that is harmful to health [137,282,761]. ...
... Each of the above methods has advantages and disadvantages. Ozone can react with a variety of organic substances due to its strong oxidizing property and has the effect of disinfection and sterilization (Bertol et al., 2012;Kwong et al., 2008), but its irritation is harmful to the human body, and the reactants can also cause secondary pollution (Hubbard et al., 2005). The photocatalytic oxidation technology based on ultraviolet light and photocatalyst can remove indoor air pollutants through the reaction of oxidant hydroxyl radicals and superoxide anion radicals, and also has the ability to remove bacteria and viruses (Mamaghani et al., 2017;Martinez-Montelongo et al., 2020;Yu and Brouwers, 2009). ...
Indoor air purification received more attention recently. In this study, the effects of six common indoor ornamental plants (Epripremnum aureum, Chlorphytum comosum, Aloe vera, Sedum sediforme, Cereus cv. Fairy Castle, and Sedum adolphii) and three kinds of microalgae (Chlorella sp. HQ, Scenedesmus sp. LX1, and C. vulgaris) on the removal of four types of air pollutants (particulate matters less than 2.5 (PM2.5) and 10 μm (PM10) in size, formaldehyde (HCHO) and total volatile organic compounds (VOCS)) in test chamber compared with common physical purification methods (high efficiency particulate air filter and nano activated carbon absorption) were investigated. Their effects on oxygen, carbon dioxide, and relative humidity were also evaluated. The results showed that microalgae, especially C. vulgaris, was more suitable for removing PM2.5 and PM10, and the removal rates were 55.42 ± 25.77% and 45.76 ± 5.32%, respectively. The removal rates of HCHO and VOCs by all three kings of microalgae could reach 100%. Part of ornamental plants took a longer time to achieve 100% removal of HCHO and VOCs. Physical methods were weaker than ornamental plants and microalgae in terms of increased relative humidity and O2 content. In general, microalgae, especially C. vulgaris could purify indoor air pollutants more efficiently. The above studies provided data and theoretical support for the purification of indoor air pollutants by microalgae.
... 15,16 The use of ozone generators for removal of VOCs was more frequent in the 1990s. Later, it was proven that the efficiency of VOC removal with such technology was rather low 17 and more importantly, ozone has been found to contribute to the formation of harmful secondary organic aerosols 18 and can cause asthma and other health related issues in humans. 19 Adsorption and PCO have been the two methods that attract most interest in the removal and degradation of VOCs. ...
The VOCs removal from polluted air has been achieved using several different methods but primarily through the use of adsorbent materials or through degradation with photocatalytic oxidation (PCO). Fibres produced by electrospinning have the possibility to easily incorporate additives into the fibres and onto their surface. This can functionalise them for efficient VOCs removal. Cellulose acetate (CA)-based electrospun fibre membranes have been fabricated and doped with activated charcoal (AC) and titanium dioxide (TiO 2 ), either separately or in combination to investigate their toluene removal capacity of the single additive and the synergic effects of adsorption and PCO. Two different methods of functionalisation of the fibres with AC and TiO 2 have been used. These methods are air spraying and electro-spraying. Several configurations of the final membranes have been investigated. SEM images indicate that the additives have been successfully distributed on the fibre surface and they affect their morphology by increasing the overall roughness and the thickness of the final membranes. Adsorption with AC achieved 45.5% removal of toluene with a starting concentration of 22.5 ppm. PCO was probably initiated using a blacklight blue UV lamp with a peak wavelength of 365 nm as formation of formaldehyde was recorded. The findings suggest that PCO is affected by the residence time and UV light intensity.
... Removing gaseous pollutants through ozonation requires ozone levels higher than the typical exposure limits, which are detrimental [12]. Moreover, ozone's reaction with some chemical contaminants can cause hazardous byproducts (like ultrafine particles, formaldehyde, ketones, and organic acids) [13,14]. Finally, several byproducts (like particles, ozone, nitrogen oxides, carbon monoxide, and formaldehyde) and low energy efficiency make non-thermal plasma inappropriate for the indoor environment application [11,13]. ...
Adsorbent agents, which use physisorption and/or chemisorption to remove gaseous pollutants, are the most commonly used technology for indoor air purification. Several mathematical models have been developed to represent the adsorption process. An appropriate numerical simulation requires uncomplicated models with an acceptable level of error. The models should consider the filter type, operational conditions, and environmental conditions. This review covers the developed models to estimate the performance of adsorbent filters for indoor environment application over the last two decades. For this purpose, the existing models are divided into interpellate mass transfer models and kinetic models. By systematically reviewing these models, their merits, useful applications and limitations are highlighted. Specific emphasis is placed on determining the rate-limiting step(s) in the mass transfer process for both physisorbent and chemisorbent media. Then, the discussion highlights the strengths and weaknesses of currently used models for taking into account the effect of the gas mixture, relative humidity, and temperature on the performance of the filters. Finally, a summary of several future research challenges in this field of engineering is provided.
... [21] Exposure to O 3 may cause asthma as well as decreased lung function. [35] Most indoor ozone originates outdoors and enters with ventilation air, indoor emission can also contribute to increase indoor ozone concentrations; [21] for example, the indoor air purifiers can also generate O 3. [36] The O 3 concentrations indoors are usually lower than outdoor. However, these lower concentration levels indoors should not be overlooked because most people spend indoors large fractions of their time. ...
Readers will be introduced to the most common sampling and analytical techniques that are being used indoors for air quality monitoring though the simultaneous determination of several air pollutants (i.e., inorganic and organic gaseous contaminants and airborne particulate matter) and the possible challenges encountered by implementing them. Thus, i) personal exposure equipment; (ii) portable multipollutant monitors; and (iii) fixed monitoring devices have been reviewed. Besides, compiling the most common modular arrangements of instruments, multipollutant analysis approaches through time-integrated and continuous sampling performed during field campaigns organized in several indoor environments in the frame of collaborative research projects are hereby also presented. Our aim was not to compile a comprehensive review on approaches used for multipollutant indoor air quality monitoring but instead to give an overview of potentially useful instrumentation. Discussion on instruments useful for the determination of radicals and bioaerosols as well as use of sensors has been voluntary minimized.
... Different from PM and NO 2 , the F inf values of O 3 were slightly higher at homes with air purifiers than those without. Some air purifiers might produce O 3 [70][71][72]. There are two types of air purifiers used at the selected homes, including high efficiency particulate air (HEPA) filters and ultra plasma ion (UPI) filter. ...
The majority of urban residents live in places with air quality exceeding World Health Organization guidelines. To quantify infiltration of outdoor pollution, and key factors affecting it, common outdoor air pollutants (PM2.5, NO2, and O3) were measured at 49 homes in Hong Kong. Infiltration factors (Finf) were derived based on linear regression of simultaneous indoor and outdoor measurements for each pollutant at each home. Finf estimated based on data for home occupancy, during which people were actually exposed, differed by up to 22%, 73% and 63% for PM2.5, NO2 and O3, respectively, from estimates based on whole monitoring data. This indicates the importance of separating occupancy time to quantify Finf for exposure estimation. The inter-home variability in occupancy Finf ranged from 0.11 to 1.00 (mean: 0.75) for PM2.5, 0.14 to 1.00 (mean: 0.53) for NO2, and 0.05 to 0.95 (mean: 0.47) for O3. Ventilation practices (e.g., window opening duration and air-conditioning on/off) explained 48%, 20%, and 10% of the inter-home variations in PM2.5, NO2 and O3 Finf, respectively. Use of air purifiers explained an additional 8%–9% of variations for PM2.5 and NO2. Thus, there is potential to reduce outdoor infiltration by modifying occupant behaviours. Compared to PM2.5 (R² = 0.63), the developed models explained less variability in Finf for NO2 (R² = 0.40) and O3 (R² = 0.10). These two gases are chemically reactive. Further investigation, supported by additional measurements of related chemical species, is needed to improve understanding of infiltration process of reactive gases such as NO2 and O3.
... 2,3 However, the main problems of these technologies lie on their selectivity to certain VOCs and the additional disposal or handling steps. Active filtration systems are based on photocatalytic oxidation, 4 plasma processes 5 and ozone generation, 6 which aims at mineralizing VOCs. Photocatalytic oxidation induces the mineralization of VOCs by producing radical species thanks to photo-excitation of a solid catalyst under irradiation. ...
Addition of titanium dioxide (TiO2) (nano)particles in photocatalytic paints represents a promising alternative aiming to mineralize gaseous pollutants, such as Volatile Organic Compounds (VOCs), into innocuous species (H2O and CO2). Despite important industrial and economic benefit, some concerns were raised regarding the risks associated to nano-objects and their human and environmental impacts. To mitigate potential risks associated to the use of these nano-objects, we report a safer by design strategy to develop a photocatalytic paint containing TiO2 nanoparticles (NPs) taking into consideration safety aspects over its life cycle. Specific innovative types of TiO2 NPs were synthesized. These nanoparticles were then incorporated into an organic matrix-based paint. These paints were applied on standard substrates and underwent artificial weathering in an accelerated weathering chamber with controlled parameters. Photocatalytic efficiency towards airborne VOCs was measured for all paints. Mechanical solicitation through abrasion and incineration tests were performed to assess potential emission of airborne particles that could lead to human or environmental exposure. In parallel, toxicology studies were conducted to assess the hazard associated to the pristine particles and paints residues. Using this safer by design strategy, we succeeded to decrease the negative impact of TiO2 on the paint matrix while keeping a good photocatalytic efficiency and reducing the NPs release. Taken together, these results show that we succeeded in generating safer by design paints thanks to the use of these specifically developed TiO2 NPs, which hold similar photocatalytic properties and enhanced physical properties as compared to paints containing reference TiO2 NPs, while reducing their potential hazard.
... It is common for manufacturers of air cleaners to claim that their technologies can remove particles effectively. However, some studies have revealed that manufacturers' claims are not valid, and some of the technologies themselves can cause the generation of ultrafine particles [33,64,65]. ...
Many people spend most of their time in an indoor environment. A positive relationship exists between indoor environmental quality and the health, wellbeing, and productivity of occupants in buildings. The indoor environment is affected by pollutants, such as gases and particles. Pollutants can be removed from the indoor environment in various ways. Air-cleaning devices are commonly marketed as benefiting the removal of air pollutants and, consequently, improving indoor air quality. Depending on the type of cleaning technology, air cleaners may generate undesired and toxic byproducts. Different air filtration technologies, such as electrostatic precipitators (ESPs) have been introduced to the market. The ESP has been used in buildings because it can remove particles while only causing low pressure drops. Moreover, ESPs can be either in-duct or standalone units. This review aims to provide an overview of ESP use, methods for testing this product, the performance of existing ESPs concerning removing pollutants and their byproducts, and the existing market for ESPs.
... Ozone generators purposely create ozone and emit this into the indoor air to react with some pollutants, mainly biological and odour-based, through oxidation to eliminate them from the air and form less harmful substances such as carbon dioxide (CO 2 ) (Britigan et al., 2006;Hubbard et al., 2005). However, there may be serious health consequences associated with producing ozone at ground level as the properties allowing it to 'react with organic material outside the body give it the ability to react with similar organic material that makes up the body' and can lead to a range of respiratory problems (US EPA 2018a). ...
A systematic literature review was carried out to examine the impact of portable air purifiers (PAPs) on indoor air quality (PM 2.5) and health, focussing on adults and children in indoor environments (homes, schools and offices). Analysed studies all showed reductions in PM 2.5 of between 22.6 and 92.0% with the use of PAPs when compared to the control. Associations with health impacts found included those on blood pressure, respiratory parameters and pregnancy outcomes. Changes in clinical biochemical markers were also identified. However, evidence for such associations was limited and inconsistent. Health benefits from a reduction in PM 2.5 would be expected as the cumulative body of scientific evidence from various cohort studies shows positive impacts of long-term reduction in PM 2.5 concentrations. The current evidence demonstrates that using a PAP results in short-term reductions in PM 2.5 in the indoor environment, which has the potential to offer health benefits. Crown
... The earlier studies have also reported a significant correlation between indoor pollutant concentration and outdoor pollutant concentration. [8] Similarly, increased ozone levels in green buildings can be partly attributed to the air filters used to purify the indoor air which releases ozone [9,10] on reacting with certain pollutants and partly to the use of machines like photocopiers. [11,12] Higher ammonia levels in green buildings as compared to conventional buildings can be partly attributed to its proximity with the Mithi river which has been reduced to a filthy 'nullah' with increased ammonia levels. ...
Indoor air quality (IAQ) influences human health, productivity and wellness. Green buildings are believed to have better IAQ. The 'sick building syndrome' (SBS) describes a set of nonspecific symptoms experienced by occupants due to time spent in a building with poor IAQ. Thus this study was undertaken to assess the IAQ in green buildings and compare it with that of conventional buildings. The prevalence of SBS in both types of buildings is also studied. In five pairs of green and conventional buildings measurements of comfort parameters (temperature & relative humidity) and indoor air pollutants using monitors was done. 148 employees which included 84 from green buildings and 64 from conventional buildings were surveyed for SBS using an interviewer-administered questionnaire. The analysis was done using SPSS16 and included Mann Whitney for IAQ pollutant concentrations and Chi-square for the SBS prevalence. Similar indoor air quality was found in both types of buildings. The mean of temperature, CO2 and formaldehyde was statistically lower in green buildings. The SBS prevalence was found to be 38.1% in green buildings and 53.1% in conventional buildings. Thus to conclude the poorly maintained green building does not have any added advantage for occurrence of SBS.
... CC showed the strongest resistance to formaldehyde as its chlorophyll content was reduced the least. The results were consistent with other reports that plant chlorophyll content reduced when exposed to formaldehyde (Hubbard et al. 2010;Zhao and Shi 2009). This is comparable with another study that the chlorophyll content of Sansevieria trifasciata var. ...
Gaseous formaldehyde removal efficiency and physiological characteristics of leaves were investigated through a dynamic fumigation system. Three different species of potted Chlorophytum Comosum, (Green Chlorophytum Comosum for its green leaves), CC (Combined the leaves of Chlorophytum Comosum with leaves half green and half white) and PC (Purple Chlorophytum Comosum for its purple leaves), were exposed to formaldehyde for 7 days. The results showed formaldehyde removal efficiencies in the daytime were 71.07% ± 0.23, 84.66% ± 0.19, and 46.73% ± 0.15 at 1 ppm for GC, CC, and GC plants, respectively, and were 36.21% ± 0.24, 62.15% ± 0.19, and 34.97% ± 0.11 at night. This might be due to higher plant physiological activities (e.g., photosynthesis, respiration, and transpiration) during the daytime than at night. Ten physiological indicators of leaves were chosen to evaluate the 7-day fumigation process, which were chlorophyll, free protein, relative conductivity, malondialdehyde (MDA), hydrogen peroxide (H2O2), hydroxyl radical, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and total antioxidant capacity (T-AOC). Eight of these indicators increased, while chlorophyll decreased by 22.16%, 6.95%, and 25.32%, and CAT decreased by 18.9%, 17.8%, and 25.30% for GC, CC, and PC respectively. Among all the increasing physiological indicators, relative conductivity and MDA showed the greatest increase by 279.32% and 155.56% for PC. A 15-day recovery study was also conducted using MDA and T-AOC as indicators. The results showed that all the tested plants could be tolerant up to the 8 ppm of formaldehyde concentration for 7 days under dynamic fumigation and needed 10–15 days for self-recovery.
... Although once formed the ozone-initiated products are susceptible of photodegradation in the near-UV range, the removal rates are small and the lifetimes indoors are estimated to be longer than outdoors especially if adsorption occur onto indoor surfaces (Atkinson and Arey, 2003). To our knowledge, ozone-initiated chemistry has been investigated both inside small-and full-scale test emission chambers (Liu et al., 2004;Destaillats et al., 2006;Singer et al., 2006;Nørgaard et al., 2014a;Shu and Morrison, 2012), in real or simulated public places (e.g., offices, aromatherapy environments, simulated aircraft cabin) (Nørgaard et al., 2014b;Weschler and Shields, 2003;Weschler et al., 2007;Huang et al., 2012) and, finally, in private dwellings (Hubbard et al., 2005). Although risk assessment is a complex issue with a large number of factors to consider, some studies highlighted increasing concern of the use of cleaning products under certain conditions, e.g. ...
Volatile Organic Compounds (VOCs) emission and Secondary Organic Aerosols (SOA) formation from a water-based carpet deodorizer were investigated in a 20 m3 walk-in climate chamber with and without a textile carpet installed. The deodorizer was tested under near-realistic user conditions at low (< 2 ppbv) and high (~50 ppbv) ozone concentrations and controlled micro-environmental parameters. Fifty grams of the deodorizer was pump sprayed onto 2 m2 inert stainlesssteel surface or carpet in order to mimic normal use. Characterization of primary VOCs and ozone-initiated products was performed by air sampling on Tenax TA followed by TD-GC/MS analysis and on DNPH cartridges followed by liquid extraction and HPLC/UV analysis. SOA formation was monitored simultaneously by means of high-time resolution instruments. Emission testing onto steel plates at ~50 ppbv ozone showed the decay of reactive VOCs (i.e., dihydromyrcenol and linalool) concurrent with the consumption of ozone and formation of oxygenated reaction products (i.e., acetaldehyde, acetone and 6-methyl-5-hepten-2-one) and an increase of SOA. Emission testing on carpet at ~50 ppbv ozone showed a significant ozone removal and an increase of nonanal and dodecanal, but without detection of oxygenated products and SOA formation. The reactive VOCs from the carpet experiment followed a first order decay.
... In principle, ozone generators are not an efficient method for destroying pollutants at low ozone levels, being an effective approach only at unsafe, high ozone levels. The emitted levels of ozone generators are approximately 500 ppb (Hubbard et al. 2005), which is five times higher than the maximum ozone exposure reported by the World Health Organization (WHO). Boeniger 1995 also reported that the reaction time for ozone with air pollutants is very high and may last for several months or even years. ...
Photocatalysis is one of the fastest growing technologies for the treatment of pollutants, utilizing the mechanism of reaction with the help of light (photo emissions). Photocatalysis has captured broad academic and research interest during the past three decades for its potential of controlling pollution in air and water. Its qualities, such as low cost and high efficiency, have caused researchers all over the world to focus on it and also promoted many industrial applications and much research. Photocatalysis has been used to remove major air pollutants, disinfect water, and oxidize various organic chemicals. In this connection, this chapter considers the properties of the ideal photocatalyst, available photocatalytic materials for air pollution control, common indoor air pollutants and their severe health effects, and purification techniques for indoor air pollution. Furthermore, photocatalytic oxidation techniques for the removal of volatile organic compounds are discussed in detail.
... Maternal exposure to ozone and PM 2.5 will increase the prevalence of orofacial clefts [8]. In addition to the harmful effects of ozone itself, researchers have indicated that heterogeneous and homogeneous reactions between ozone and unsaturated hydrocarbons would produce secondary pollutants such as free radicals, carbonyls, carboxylic acids, and fine particles, which are more harmful to people's health [9]. Therefore, it is very necessary to reduce indoor ozone pollution. ...
Nowadays atmospheric ozone pollution increasingly occurs in summer in China developed areas. To improve catalytic stability of MnO2 for decomposing ozone in real humid environment, we developed a simple method to obtain the ammonium (NH4⁺) treated birnessite-type MnO2 (N-MnO2). NH4⁺ ions not only replaced K⁺ ions in the interlayer of MnO2 but also existed on the surface of MnO2, separating the original aggregated MnO2 nanoparticles into smaller ones. The N-MnO2 had much larger specific surface area than the original MnO2 (221 m²/g vs. 59 m²/g), leading to more oxygen vacancies and enhanced surface acidity. As a result, N-MnO2 exhibited excellent and stable activity for ozone decomposition in humid condition (relative humidity 50%) at room temperature, achieving 80% conversion of 115 ppm ozone under the space velocity as high as 600 L/gcat·h. In addition, N-MnO2 powder was successfully coated on the non-woven fabric. This composite material not only showed stable 60–80% conversion of 15 ppm ozone in a 7-day test, but also its air pressure-drop was only 3 Pa under the commonly used air filtration face velocity of 5.3 cm/s. Thus, as-synthesized N-MnO2 showed great potential in real building ventilation system to prevent ozone pollution from outdoor air.
... [54] It should be noted that several studies have shown that many indoor VOC pollutants could not be efficiently removed by the concentration of indoor ozone in the range 50-100 ppbv (typical exposure limits) and under low VOC and ozone concentration levels, the reaction rate might be too low to be effective for most indoor VOCs, while exposure to high concentration of ozone can have a harmful effect on human health [55] . Moreover, Hubbard et al. [56] have reported that the use of ozone generators in homes could generate secondary organic aerosols, especially in the presence of terpenes (usually present in cleaning agents and deodorizers). [4] ...
Compared with other approaches for the removal of VOCs, the concept of “storage‐regeneration” cycling is proposed as an effective and promising way to eliminate low‐concentration indoor VOCs. A key issue in this approach is the design of catalytic materials which should possess balanced properties between storage and regeneration. The materials used for the storage of VOCs such as formaldehyde and benzene should not only possess high and selective VOC storage capacity, but also be easily regenerated without any release of the VOCs or generation of secondary pollutants. To this end, appropriate regeneration methods have been proposed, including thermal regeneration, plasma (nonthermal plasma) oxidation or ozone enabled regeneration. In this short review, these essential features of the cycled “storage‐regeneration” concept for VOC destruction are considered and the prospects for the implementation of this technology are assessed.
... Oxygen molecules are exposed to a corona discharge or UV-irradiation to produce ozone, which will be able to eliminate odours and microbial agents due to the oxidising properties [5]. However, studies have shown that indoor ozone concentrations in the range 50-100 ppb v (exposure limits) does not guarantee an efficient removal of indoor VOC pollutants [51]. Moreover it appeared that this technique cannot compete with moderate ventilation. ...
TiO2 and Ag nanoparticle multilayered films were constructed on model substrates and textiles via Layer-by-Layer (LbL) assembly. The TiO2 nanoparticle based films constructed on model substrates showed a non-conventional photocatalytic behaviour for gas phase formic acid mineralisation upon UV-A irradiation, and a high mineralisation was obtained for a single layer TiO2 nanoparticle film. These films also showed biocidal properties upon UV-A irradiation. The elaboration of a one-pot method, combining the photo-induced synthesis of Ag nanoparticles and the LbL deposition of TiO2 nanoparticle layer, allowed the direct synthesis of Ag nanoparticles within the films and a high enhancement of the film photocatalytic properties. The construction methods were successfully transfered on textile surfaces. The films were photocatalytically active and biocidal under UV-A irradiation after several washing treatment cycles.
... Ozone could initiate oxidation processes on the surface of loaded filters in air handling system, and the products lead to an increase in countable particles of downstream [7]. Incompletely decomposed VOCs by UV-PCO air cleaners may transform to other secondary pollutants including formaldehyde, acetaldehyde, propionaldehdye and crotonaldehyde [8] secondary organic aerosol (SOA) was also measured from reaction between air-cleaner-generated ozone and olefins from environment [9]. ...
... In some cases, ozone can reach high mixing ratios (e.g., a few hundred ppb) in buildings with the operation of devices such as photocopiers, laser printers and air purifiers. 15,16,17 Unsaturated organic species in cigarette smoke can react with ozone to form less volatile secondary products and thus change particle size distribution and composition. Indeed, Sleiman et al. have reported an initial observation that ultrafine particle formation accompanies cigarette smoke oxidation by ozone. ...
Cigarette smoke is an important source of particles and gases in the indoor environment. In this work, aging of side-stream cigarette smoke was studied in an environmental chamber via exposure to ozone (O3), hydroxyl radicals (OH) and indoor fluorescent lights. Aerosol mass concentrations increased by 13-18% upon exposure to 15 ppb O3 and by 8-42% upon exposure to 0.45 ppt OH. Ultrafine particle (UFP) formation was observed during all ozone experiments, regardless of the primary smoke aerosol concentration (185 to 1950 µg m⁻³). During OH oxidation, however, UFP formed only when the primary particle concentration was relatively low (< 130 µg m⁻³) and the OH concentration was high (~1.1 x 10⁷ molecules cm⁻³). Online aerosol composition measurements show that oxygen- and nitrogen- containing species were formed during oxidation. Gas phase oxidation of NO to NO2 occurred during fluorescent light exposure, but neither primary particle growth nor UFP formation were observed. Overall, exposure of cigarette smoke to ozone will likely lead to UFP formation in indoor environments. On the other hand, UPF formation via OH oxidation will only occur when OH concentrations are high (~107 molecules cm⁻³), and is therefore less likely to have an impact on indoor aerosol associated with cigarette smoke.
... Ozone could initiate oxidation processes on the surface of loaded filters in air handling system, and the products lead to an increase in countable particles of downstream [7]. Incompletely decomposed VOCs by UV-PCO air cleaners may transform to other secondary pollutants including formaldehyde, acetaldehyde, propionaldehdye and crotonaldehyde [8] secondary organic aerosol (SOA) was also measured from reaction between air-cleaner-generated ozone and olefins from environment [9]. ...
As a result of industrialization, urbanization, and human activity, hydrocarbon waste is a ubiquitous and oftentimes overlooked hazard to the biosphere. With an emphasis on its pervasive existence in ecosystems across the world, this study investigates the origins, characteristics, destiny, and environmental effects of hydrocarbon waste. To devise effective mitigation strategies, it is essential to have a comprehensive understanding of the sources of hydrocarbon waste. Persistence and toxicity in the environment may be understood by analyzing the many characteristics of hydrocarbon waste, such as its chemical makeup and physical attributes. The impact on ecosystems, animals, and human health is highlighted in the paper, underscoring the necessity of thorough risk assessments and regulatory frameworks. Assessing the environmental impact encompasses its role in climate change, upsets of natural equilibrium, and contamination of soil and water resources. The present chapter is also spotlighted on environmental management and sustainable practices, mitigating the unseen threat to our biosphere.
Air pollution and human exposure to poor air quality rank nowadays as the most serious environmental threats to public health worldwide. Botanical biofiltration using active green walls based on air-purifying plants can support an effective control of indoor air pollution. This study focuses on the design and evaluation of the performance of an active botanical filter for the removal of acetone, toluene and α-pinene at low concentrations using the houseplant Epipremnum aureum (commonly known as golden Pothos). The botanical filter was constructed with a vertical polyurethane foam wall supporting Pothos, and internal mineral salt medium and air recirculation. Maximum steady state removal efficiencies of 99.8 ± 0.8%, 83.6 ± 7.3% and 71.1 ± 5.2% were recorded for acetone, α-pinene and toluene, respectively. The reduction in the gas recirculation flow rate through the wall from 36 to 0 L min-1 decreased the removal efficiency of α-pinene to 70.37 ± 1.72%, while acetone and toluene maintained their removal efficiency under these conditions. Reducing the internal recirculation rate of the nutrient medium from 1.50 to 0.95 L min-1 and the absence of Photos in the polyurethane wall of the biofilter also decreased the pollutant abatement efficiency of the botanical filter. In addition, the analysis of the microbial community composition revealed significant differences in microbial composition and differences in the relative abundances between liquid samples of the medium in which the plant species grew and the mineral salt medium recirculated across the biofilter, which might contribute to the pollutant removal mechanisms.
The irregular operations as a part of the hybrid warfare have been historically augmented by the use of biological amenities, may these be bioagents proper or toxins, to attain destructive but, more so, increasingly and disproportionally disruptive effects. The institutionalized murder (a.k.a. “leadership attacks”) seems to get traction within the last 50 years with assassinations of civilian targets (dubbed “terrorists”), and military ones without any formal or informal state-of-war and are implemented by military amenities, such as armed UAVs, by secret agents possibly of paramilitary stock, and by recruited local or imported operatives/contractors, from a mercenary market or a wide pool of dissidents. This assassination spree would be bolstered by the use of bioagents, cellular (microbial agents) or molecular (biochemical agents), which would allow clandestine application and would provide, upon request and design, a delay of the initiation of the results, allowing the perpetrators to escape and providing deniability to the contracting authority. World history, especially its aspects residing into lore and occult, seem to recount many such cases, if testimony is read properly. The same effect, multiplied due to the technological advancements in both delivery and engineering of bioagents, may be a very destabilizing and ruthlessly effective means, capable of causing Global Catastrophic BioEvents, Extinction Level Events or, at the very least, communal, societal and state collapses by targeted delivery to key human, environmental and agricultural targets.
The Chemical Assessment of Surfaces and Air (CASA) study aimed to understand how chemicals transform in the indoor environment using perturbations (e.g., cooking, cleaning) or additions of indoor and outdoor...
Zusammenfassung
Die von der Gesellschaft für Hygiene, Umweltmedizin und Präventivmedizin (GHUP) federführend aktualisierte Leitlinie „Medizinisch klinische Diagnostik bei Schimmelpilzexposition in Innenräumen – Update 2023“ ist Gegenstand des vorliegenden Beitrags. Schimmelwachstum im Innenraum ist als ein potenzielles Gesundheitsrisiko zu betrachten, auch ohne dass ein quantitativer und/oder kausaler Zusammenhang zwischen dem Vorkommen einzelner Arten und Gesundheitsbeschwerden gesichert werden kann. Es liegt keine Evidenz für einen kausalen Zusammenhang zwischen Feuchte-/Schimmelschäden und Krankheiten des Menschen vor. Wesentliche Gründe dafür sind das ubiquitäre Vorkommen von Schimmelpilzen und und bislang unzureichende diagnostische Methoden. Es liegt lediglich ausreichende Evidenz für folgende Assoziationen von Feuchte-/Schimmelschäden und folgenden Erkrankungen vor: allergische Atemwegserkrankungen, allergische Rhinitis, allergische Rhinokonjunktivitis, Allergische bronchopulmonale Aspergillose (ABPA), andere Allergische bronchopulmonale Mykosen (ABPM), Aspergillom, Aspergillus-Bronchitis, Asthma (Manifestation, Progression, Exazerbation), Begünstigung von Atemwegsinfekten, Bronchitis (akut, chronisch), Community-acquired Aspergillus-Pneumonie, Exogen-allergische Alveolitis (EAA), invasive Aspergillosen, Mykosen, Organic Dust Toxic Syndrome (ODTS) [Arbeitsplatzexposition], pulmonale Aspergillose (subakut, chronisch) und Rhinosinusitis (akut, chronisch invasiv oder granulomatös, allergisch). Dabei ist das sensibilisierende Potenzial von Schimmelpilzen im Vergleich zu anderen Umweltallergenen deutlich geringer einzuschätzen. Aktuelle Studien zeigen europaweit eine vergleichsweise geringe Sensibilisierungsprävalenz von 3–22,5 % gemessen an der Gesamtbevölkerung. Eingeschränkte oder vermutete Evidenz für eine Assoziation liegt vor hinsichtlich des atopischen Ekzems (atopische Dermatitis, Neurodermitis, Manifestation), Befindlichkeitsstörungen, chronisch obstruktive Lungenerkrankung (COPD), Geruchswirkungen, Mucous Membrane Irritation (MMI) und Sarkoidose. Inadäquate oder unzureichende Evidenz für eine Assoziation liegt vor für akute idiopathische pulmonale Hämorrhagie bei Kindern, Arthritis, Autoimmunerkrankungen, chronisches Müdigkeitssyndrom (CFS), Endokrinopathien, gastrointestinale Effekte, Krebs, luftgetragen übertragene Mykotoxikose, Multiple chemische Sensitivität (MCS), Multiple Sklerose, neuropsychologische Effekte, neurotoxische Effekte, plötzlicher Kindstod, renale Effekte, Reproduktionsstörungen, Rheuma, Schilddrüsenerkrankungen, Sick-Building-Syndrom (SBS), Teratogenität und Urtikaria. Das Infektionsrisiko durch die in Innenräumen regelmäßig vorkommenden Schimmelpilzarten ist für gesunde Personen gering, die meisten Arten sind in die Risikogruppe 1 und wenige in 2 (Aspergillus fumigatus, Aspergillus flavus) der Biostoffverordnung eingestuft. Nur Schimmelpilze, die potenziell in der Lage sind, Toxine zu bilden, kommen als Auslöser einer Intoxikation in Betracht. Ob im Einzelfall eine Toxinbildung im Innenraum stattfindet, entscheiden die Umgebungs- und Wachstumsbedingungen und hier vor allem das Substrat. Von Geruchswirkungen und/oder Befindlichkeitsstörungen kann bei Feuchte-/Schimmelschäden im Innenraum grundsätzlich jeder betroffen sein. Hierbei handelt es sich nicht um eine akute Gesundheitsgefährdung. Prädisponierende Faktoren für Geruchswirkungen können genetische und hormonelle Einflüsse, Prägung, Kontext und Adaptationseffekte sein. Prädisponierende Faktoren für Befindlichkeitsstörungen können Umweltbesorgnisse, -ängste, -konditionierungen und -attributionen sowie eine Vielzahl von Erkrankungen sein. Besonders zu schützende Risikogruppen bezüglich eines Infektionsrisikos sind Personen unter Immunsuppression nach der Einteilung der Kommission für Krankenhaushygiene und Infektionsprävention (KRINKO) beim Robert Koch-Institut (RKI), Personen mit schwer verlaufender Influenza, Personen mit schwer verlaufender COVID-19 und Personen mit Mukoviszidose (zystischer Fibrose), bezüglich eines allergischen Risikos Personen mit Mukoviszidose (zystischer Fibrose) und Personen mit Asthma bronchiale. Die rationale Diagnostik beinhaltet die Anamnese, eine körperliche Untersuchung, eine konventionelle Allergiediagnostik einschließlich gegebenenfalls Provokationstests. Zum Vorgehen bei Schimmelpilzinfektionen wird auf die entsprechenden Leitlinien verwiesen. Hinsichtlich der Mykotoxine existieren zurzeit keine brauchbaren und validierten Testverfahren, die in der klinischen Diagnostik eingesetzt werden könnten. Präventivmedizinisch ist wichtig, dass Schimmelpilzbefall in relevantem Ausmaß aus Vorsorgegründen nicht toleriert werden darf. Zur Beurteilung des Schadensausmaßes und zum Vorgehen wird auf den „Schimmelpilzleitfaden“ des Umweltbundesamtes verwiesen.
Indoor environmental quality (IEQ), often shortened indoor air quality, is characterized by the spatial and temporal variability of pollutants, physical and biological factors in the various indoor spaces, as well as the thermal and structural conditions of the building, environmental influences, and also by the behavior and activities of the room users. This chapter provides an initial overview of basic aspects of the relationship between IEQ and health especially in schools. In addition, the so-called sick building syndrome is explained in more detail, which is a building-related health disorder that summarizes non-specific indoor-related health problems for both groups of people and individuals in commercial, public, and private buildings. Moreover, this chapter aims to present basic effects of indoor climate on our well-being indoors and discusses the effects of the dramatic climate change and its impact on human health.
Due to the very often high temporal and spatial variability of indoor conditions complex chemical formation and transformation processes occur in this microenvironment. This includes processes of deposition on the room surfaces and partly reaction with the surfaces, re-release to the room air, but also transformation of substances and new formation of the so-called secondary organic aerosols (SOA). Although these processes are not yet fully understood due to their diversity, they may be relevant to the exposure of the indoor room users.
It is of particular importance that indoor sampling and measurements should only ever be carried out with a clear question in mind and a defined measurement plan. With this in mind, the different sampling techniques and more new passive sampler devices like the wristband technology were discussed in brief.
There is a large body of scientific publications, especially on the subject of ventilation of indoor spaces. The focus is on ventilation and air purification methods, but here only a first overview can be given and reference is made to more detailed literature.
Nowadays, people spend 80-90% of their time indoors, while recent policies on energy efficient and safe buildings require reduced building ventilation rates and locked windows. These facts have raised a growing concern on indoor air quality, which is currently receiving even more attention than outdoors pollution. Prevention is the first and most cost-effective strategy to improve indoor air quality, but once pollution is generated, a battery of physicochemical technologies is typically implemented to improve air quality with a questionable efficiency and at high operating costs. Biotechnologies have emerged as promising alternatives to abate indoor air pollutants, but current bioreactor configurations and the low concentrations of indoor air pollutants limit their widespread implementation in homes, offices and public buildings. In this context, recent investigations have shown that potted plants can aid in the removal of a wide range of indoor air pollutants, especially volatile organic compounds (VOCs), and can be engineered in aesthetically attractive configurations. The original investigations conducted by NASA, along with recent advances in technology and design, have resulted in a new generation of botanical biofilters with the potential to effectively mitigate indoor air pollution, with increasing public aesthetics acceptance. This article presents a review of the research on active botanical filters as sustainable alternatives to purify indoor air.
A healthy indoor environment is critical for children due to the severe effect of poor indoor air quality (IAQ) on their overall well-being. Day-care centres (DCCs) are important indoor microenvironments for children apart from their homes. Therefore, monitoring IAQ in this microenvironment is vital because of the vulnerability of the occupants. This review gives a global overview of the predominant indoor chemical pollutant levels monitored in DCCs, compares their concentration with available regulations for IAQ, evaluates the sources and health risk effects of chemical pollutants and proposes strategies for enhancing IAQ in DCCs. Thirty-seven (37) articles were used based on specific stated inclusion and exclusion criteria. Continents like Europe and Asia have the most published studies in indoor DCCs. The decreasing trend of pollutants examined in most studies include particulate matter > carbon dioxide > formaldehyde > carbon monoxide > total volatile organic compounds > volatile organic compounds > nitrogen dioxide > ozone > benzene > sulphur dioxide = radon. Particulate matter in the size and mass concentration range of PM10 (0.116–1920.71 μg/m³) > PM2.5 (0.279.2–260.74 μg/m³) was the most investigated pollutant. While nitrogen dioxide, radon and carbon monoxide were consistent with the existing national and international reference values for IAQ across the continents, exceedances occurred in other pollutants. The limited number of indoor chemical pollutant studies suggests the need for more comprehensive studies on IAQ in DCC globally. Further studies should highlight the availability of low-cost sensors and mobile analytical equipment that will promote affordable ground-level data accessibility.
Volatile organic compounds (VOCs) are a class of hazardous gaseous materials emitted from certain solids or liquids. They are thought to possess serious short- or long-term adverse effects on human health. Nowadays, an energy-efficient and cost-effective volatile organic compound removal system is of absolute necessity due to its adverse effects. In this regard, solar or waste heat-driven adsorption-based technologies can provide an energy-efficient system; however, most of the time, their utilization is limited by the high cost of the adsorbent materials. Right now, only one commercial high-grade activated carbon named Maxsorb III is known to have high capturing capacities. The purchasing cost of this adsorbent is very high, and it is derived from a non-renewable source. Therefore, this study is intended for the quest for low-priced biomass-derived activated carbons for an energy-efficient and cost-effective VOCs removal system. Two biomass-derived activated carbons synthesized from mangrove wood and waste palm trunk precursors are chosen, and four types of VOCs (ethanol, dichloromethane, acetone, and ethyl acetate) adsorption onto them are measured experimentally using the inverse gas chromatography technique. The zero uptake adsorption enthalpy and specific entropy of the adsorption are theoretically computed for all the adsorbent/adsorbate pairs. After that, these data are compared with the obtained data for Maxsorb III to assess the performance of the biomass-derived activated carbons. Results show that, for all the VOCs, the cost-effective mangrove-based activated carbon can be an excellent alternative to the high-priced Maxsorb III when employed as an adsorbent material for VOCs removal.
Humans spend more than 80% of their lives indoors resulting in an increased demand for high indoor air quality (IAQ). At the same time, indoor air tends to be at least twice as polluted as outdoor air, and health threats caused by long-term exposure to indoor air pollution are rising. Few experiments under real-life conditions have demonstrated positive effects of indoor plants on parameters related to IAQ, resulting in improved humidity and temperature, reduced particulate matter concentration and CO2 levels. Indoor living walls allow the presence of many plants—without taking up valuable floor area. This article presents the results of conducted measurements on four do-it-yourself green walls planted with different plant species that are typically used for vertical indoor greenery (golden pothos, Boston fern, spider plant and a combination of plants) in a school setting. Besides the parameters of air humidity and temperature, CO2, mold spore and particulate matter levels, influences on room acoustics were investigated. Based on a custom-developed evaluation matrix, the plants were compared with each other and a reference without plants. The results show that no species led to deterioration of IAQ. Golden pothos had the most substantial effect and delivered improvements in all examined parameters.
To achieve carbon neutrality, it is necessary to control carbon-based gas emissions to the atmosphere. Among the various carbon-based gas removal technologies reported to date, adsorption is considered one of the most promising because of its economic efficiency, reusability, and low energy consumption. Activated carbon is widely used to treat different types of carbon-based gases owing to its large specific surface area, abundant functional groups, and strong adsorption capacity. This paper reviews the recent research progress into activated carbon as an adsorbent for carbon-based gases. The key factors (i.e., specific surface area, pore structure, and surface functional groups) affecting the adsorption of carbon-based gases by activated carbon were analyzed. The main methods employed to modify activated carbon (i.e., surface oxidation, surface reduction, loading materials, and plasma modification methods) to improve its adsorption capacity are also discussed herein, along with the targeted applications of such material in the adsorption of different types of carbon-based gases (such as aldehydes, ketones, aromatic hydrocarbons, halogenated hydrocarbons, and carbon-based greenhouse gases). Finally, the future development directions and challenges of activated carbon are discussed. Our work will be expected to benefit the development of activated carbon exhibiting selective adsorption properties, and reduce the production costs of adsorbents.
This chapter discusses indoor air quality (IAQ) in nonindustrial buildings. Historically, the concept of IAQ has included viewpoints that the introduction of outdoor air, via passive and mechanical ventilation, is required both to prevent the buildup of contaminants and the associated adverse health effects, as well as to provide for comfort of occupants. It has been observed that airborne contagious diseases and malodor are more prominent in crowded spaces with insufficient ventilation and poor or nonexistent control of contaminant sources. The International Building Code (IBC), the International Residential Code (IRC), the International Mechanical Code (IMC), and the American Society of Heating, Refrigeration and Air‐Conditioning Engineers (ASHRAE) Standards 62.1 and 62.2 recommend approaches to the control of contaminant sources and the provision of outdoor air ventilation to lower the risk of occupant dissatisfaction and diseases. The varied approaches that can be used during IAQ evaluations reflect the multitude of different problems that can occur in buildings. In developing countries, higher morbidity and mortality have multifactorial causes, with contaminated food, water, and air as major risk factors. The chapter focuses on IAQ evaluation protocols and various guidelines.
Ozonation is a common remediation approach to eliminate odors from mold, tobacco and fire damage in buildings. Little information exists to: 1) assess its effectiveness; 2) provide guidance on operation conditions; and 3) identify potential risks associated with the presence of indoor ozone and ozonation byproducts. The goal of this study is to evaluate chemical changes in thirdhand smoke (THS) aerosols induced by high levels of ozone, in comparison with THS aerosols aged under similar conditions in the absence of ozone. Samples representing different stages of smoke aging in the absence of ozone, including freshly emitted secondhand smoke (SHS) and THS, were collected inside an 18-m³ room-sized chamber over a period of 42 h after six cigarettes were consumed. The experiments involved collection and analysis of gas phase species including volatile organic compounds (VOCs), volatile carbonyls, semivolatile organic compounds (SVOCs), and particulate matter. VOC analysis was carried out by gas chromatography/mass spectrometry with a thermal desorption inlet (TD-GC/MS), and volatile carbonyls were analyzed by on-line derivatization with dinitrophenylhydrazine (DNPH), followed by liquid chromatography with UV/VIS detection. SVOCs were extracted from XAD-coated denuders and Teflon-coated fiberglass filters in the absence of ozone. In those extracts, tobacco-specific nitrosamines (TSNAs) and other SVOCs were analyzed by gas chromatography with positive chemical ionization-triple quadrupole mass spectrometric detection (GC/PCI-QQQ-MS), and polycyclic aromatic hydrocarbons (PAHs) were quantified by gas chromatography with ion trap mass spectrometric detection (GC/IT-MS) in selected ion monitoring mode. Particulate matter concentration was determined gravimetrically. In a second experiment, a 300 mg h⁻¹ commercial ozone generator was operated during 1 h, one day after smoke was generated, to evaluate the remediation of THS by ozonation. VOCs and volatile carbonyls were analyzed before and after ozonation. Extracts from fabrics that were exposed in the chamber before and after ozonation as surrogates for indoor furnishings were analyzed by GC/IT-MS, and aerosol size distribution was studied with a scanning mobility particle sizer. Ozone concentration was measured with a photometric detector. An estimated 175 mg ozone reacted with THS after 1 h of treatment, corresponding to 58% of the total O3 released during that period. Fabric-bound nicotine was depleted after ozonation, and the surface concentration of PAHs adsorbed to fabric specimens decreased by an order of magnitude due to reaction with ozone, reaching pre-smoking levels. These results suggest that ozonation has the potential to remove harmful THS chemicals from indoor surfaces. However, gas phase concentrations of volatile carbonyls, including formaldehyde, acetaldehyde and acetone were higher immediately after ozonation. Ultrafine particles (UFP, in most cases with size <60 nm) were a major ozonation byproduct. UFP number concentrations peaked shortly after ozonation ended, and remained at higher-than background levels for several hours. Based on these results, minimum re-entry times after ozone treatment were predicted for different indoor scenarios. Clearly defining re-entry times can serve as a practical measure to prevent acute exposures to ozone and harmful ozonation byproducts after treatment. This study evaluated potential benefits and risks associated with THS remediation using ozone, providing insights into this technology.
(1) Background: On the Internet, we can find the guidelines for homemade air purifiers. One of the solutions includes the use of a low-cost ozone generator to decrease the level of odors and biological contaminants. However, the authors do not notify about hazardous effects of ozone generation on human health; (2) Methods: We elaborated our test results on the bacterial and fungal aerosol reduction by the use of two technical solutions of homemade air purifiers. First, including a mesh filter and ozone generator, second including an ozone generator, mesh filter, and carbon filter. (4) Conclusions: After 20 minutes of ozone generation, the concentration of bacteria decreased by 78% and 48% without and with a carbon filter, while fungi concentration was reduced in the lower range 63% and 40%, respectively. Based on our test results, we proposed a precise periodical operation of homemade air purifier to maintain the permissible level of ozone for the occupants.
Oil pollutants, due to their toxicity, mutagenicity, and carcinogenicity, are considered a serious threat to human health and the environment. Petroleum hydrocarbons compounds, for instance, benzene, toluene, ethylbenzene, xylene, are among the natural compounds of crude oil and petrol and are often found in surface and underground water as a result of industrial activities, especially the handling of petrochemicals, reservoir leakage or inappropriate waste disposal processes. Methods based on the conventional wastewater treatment processes are not able to effectively eliminate oil compounds, and the high concentrations of these pollutants, as well as active sludge, may affect the activities and normal efficiency of the refinery. The methods of removal should not involve the production of harmful secondary pollutants in addition to wastewater at the level allowed for discharge into the environment. The output of sewage filtration by coagulation and dissolved air flotation (DAF) flocculation can be transferred to a biological reactor for further purification. Advanced coagulation methods such as electrocoagulation and flocculation are more advanced than conventional physical and chemical methods, but the major disadvantages are the production of large quantities of dangerous sludge that is unrecoverable and often repelled. Physical separation methods can be used to isolate large quantities of petroleum compounds, and, in some cases, these compounds can be recycled with a number of processes. The great disadvantage of these methods is the high demand for energy and the high number of blockages and clogging of a number of tools and equipment used in this process. Third-party refinement can further meet the objective of water reuse using methods such as nano-filtration, reverse osmosis, and advanced oxidation. Adsorption is an emergency technology that can be applied using minerals and excellent materials using low-cost materials and adsorbents. By combining the adsorption process with one of the advanced methods, in addition to lower sludge production, the process cost can also be reduced.
A synergistically combined process was studied for the removal of multi-pollutants in indoor air. Technologies including electrostatic precipitation and catalytic decomposition were integrated and investigated in a 3 m³ environmental chamber. Various sources of pollutants including cigarette smoke and building material were used to generate contaminants with complex composition. Simultaneous and effective removal of particulate matter, VOCs and ozone were achieved. The effective combination of the technologies synergistically improved the decontamination performance. Electrostatic precipitation removed particulate matter (94%-100% removal), while UV-catalysts oxidized VOCs (100% removal) within 20 min. In addition, during this process, the precipitator and VUV lights produced ozone (up to 360 ppb), initiated ozone-catalytic oxidation of gaseous pollutants, consequently enhanced the removal of VOCs. Moreover, an ozone depleting module was installed downstream to decompose the residual ozone, ensuring no ozone was released into ambient air. Notably, comparing with other reported works, the gas hourly space velocity in this work was high as 594,000 h⁻¹, while the contact time of pollutants on the catalyst was short as 0.02 s. However, simultaneous and effective removal of real and complex pollutants was achieved under such circumstance. The experimental results also suggest that the combined process can effectively improve the indoor air quality.
Recent studies have shown that nanoscale particulate matter produced in commercial charbroiling processes represents a serious health hazard and has been linked to various forms of cancer and cardiopulmonary disease. In this study, we propose a highly effective method for treating restaurant smoke emissions using a transient pulsed plasma reactor produced by nanosecond high voltage pulses. We measure the size and relative mass distributions of particulate matter (PM) produced in commercial charbroiling processes (e.g., cooking of hamburger meat) both with and without the plasma treatment. Here, the plasma discharge is produced in a 3" diameter cylindrical reactor with a 5-10 ns high voltage (17 kV) pulse generator. The distribution of untreated nanoparticle sizes is peaked around 125-150 nm in diameter, as measured using a scanning mobility particle sizer (SMPS) spectrometer. With plasma treatment, we observe up to a 55-fold reduction in relative particle mass and a significant reduction in the nanoparticle size distribution using this method. The effectiveness of the nanoscale PM remediation increases with both the pulse repetition rate and pulse voltage, demonstrating the scalability of this approach for treating particulate matter at higher flow rates and larger diameter reactors.
Cited By (since 1996): 63
,
Export Date: 4 February 2013
,
Source: Scopus
, The following values have no corresponding Zotero field:
Author Address: EPRI, 3412 Hillview Avenue, Palo Alto, CA 94304-1395, United States
Author Address: UMDNJ/R. W. J. Med. Sch./Rutgers, Department of Environmental Medicine, Piscataway, NJ, United States
Author Address: Harvard School of Public Health, Department of Environmental Health, Landmark Center, Boston, MA, United States
Formaldehyde, an air contaminant found in many indoor air investigations, poses distinct occupational exposure hazards in certain job categories (e.g., mortuary science) but is also of concern when found or suspected in office buildings and homes. A variety of air-purifying devices (APDs) are currently available or marketed for application to reduce or remove concentrations of a variety of indoor air pollutants through the use of ozone as a chemical oxidant. An investigation was conducted to determine if concentrations of formaldehyde similar to those found in industrial hygiene evaluations of funeral homes could be reduced with the use of an ozone-generating APD. An ozone-generating APD was placed in an exposure chamber and formaldehyde-containing embalming solution was allowed to evaporate naturally, creating peak and mean chamber concentrations of 2.5 and 1.3 ppm, respectively. Three 90-minute evaluations were conducted to establish a change in concentration for formaldehyde generated in the chamber. To ensure air mixing, a fan on the APD was allowed to run but the ozone-generating electrostatic plates were removed. After baseline concentration curves for formaldehyde were determined, the electrostatic plates were installed in the APD and the reproducibility of static concentrations of approximately 0.5 ppm ozone was evaluated. In a third evaluation, ozone was introduced into the chamber when formaldehyde was present at peak concentrations of 2.5 ppm. Continuous-reading instruments were used to sample for formaldehyde and ozone. Active sampling methods were also used to sample simultaneously for formaldehyde and a possible reactant product, formic acid. Triplicate measurements were made in each of three evaluations: formaldehyde alone, ozone alone, and formaldehyde and ozone combined. Concentrations of formaldehyde were virtually identical with and without 0.5 ppm ozone. No reduction in formaldehyde concentration was found during a 90-minute evaluation using ozone at this concentration with peak and average concentrations of approximately 2.5 and 1.3 ppm formaldehyde, respectively. The results of this investigation suggest that the use of ozone is ineffective in reducing concentrations of formaldehyde. Because ozone has demonstrated health hazards, and is a regulated air contaminant in both the occupational and ambient environment, the use of ozone as an air purification agent in indoor air does not seem warranted.
Health and pollution control professionals and the general public need to develop a more complete understanding of the health effects of ozone (O3) because: 1) we have been unable to significantly reduce ambient O3 levels using current strategies and controls; 2) in areas occupied by more than half of the U.S. population, current peak ambient O3 concentrations are sufficient to elicit measurable transient changes in lung function, respiratory symptoms, and airway inflammation in healthy people engaged in normal outdoor exercise and recreational activities; 3) the effects of O3 on transient functional changes are sometimes greatly potentiated by the presence of other environmental variables; and 4) cumulative structural damage occurs in rats and monkeys exposed repetitively to O3 at levels within currently occurring ambient peaks, and initial evidence from dosimetry models and interspecies comparisons indicate that humans are likely to be more sensitive to O3 than rats. The extent and significance of these effects, and the multibillion dollar costs of ambient O3 controls need to be considered in any future revisions of ambient standards and the Clean Air Act. The transient effects of O3 are more closely related to cumulative daily exposure than to one hour peak concentrations, and future revisions of the ambient standard for O3 should take this into account. The effects of long-term chronic exposure to O3 remain poorly defined, but recent epidemiologic and animal inhalation studies suggest that current ambient levels are sufficient to cause premature aging of the lungs. More research is needed to determine the need for a standard with a seasonal or annual average concentration limit.
Little information currently exists regarding the occurrence of secondary organic aerosol formation in indoor air. Smog chamber studies have demonstrated that high aerosol yields result from the reaction of ozone with terpenes, both of which commonly occur in indoor air. However, smog chambers are typically static systems, whereas indoor environments are dynamic. We conducted a series of experiments to investigate the potential for secondary aerosol in indoor air as a result of the reaction of ozone with d-limonene, a compound commonly used in air fresheners. A dynamic chamber design was used in which a smaller chamber was nested inside a larger one, with air exchange occurring between the two. The inner chamber was used to represent a model indoor environment and was operated at an air exchange rate below 1 exchange/hr, while the outer chamber was operated at a high air exchange rate of approximately 45 exchanges/hr. Limonene was introduced into the inner chamber either by the evaporation of reagent-grade d-limonene or by inserting a lemon-scented, solid air freshener. A series of ozone injections were made into the inner chamber during the course of each experiment, and an optical particle counter was used to measure the particle concentration. Measurable particle formation and growth occurred almost exclusively in the 0.1-0.2 microm and 0.2-0.3 microm size fractions in all of the experiments. Particle formation in the 0.1-0.2 microm size range occurred as soon as ozone was introduced, but the formation of particles in the 0.2-0.3 microm size range did not occur until at least the second ozone injection occurred. The results of this study show a clear potential for significant particle concentrations to be produced in indoor environments as a result of secondary particle formation via the ozone-limonene reaction. Because people spend the majority of their time indoors, secondary particles formed in indoor environments may make a significant contribution to overall particle exposure. This study provides data for assessing the impact of outdoor ozone on indoor particles. This is important to determine the efficacy of the mass-based particulate matter standards in protecting public health because the indoor secondary particles can vary coincidently with the variations of outdoor fine particles in summer.
Because human activities impact the timing, location, and degree of pollutant exposure, they play a key role in explaining exposure variation. This fact has motivated the collection of activity pattern data for their specific use in exposure assessments. The largest of these recent efforts is the National Human Activity Pattern Survey (NHAPS), a 2-year probability-based telephone survey (
n=9386) of exposure-related human activities in the United States (U.S.) sponsored by the U.S. Environmental Protection Agency (EPA). The primary purpose of NHAPS was to provide comprehensive and current exposure information over broad geographical and temporal scales, particularly for use in probabilistic population exposure models. NHAPS was conducted on a virtually daily basis from late September 1992 through September 1994 by the University of Maryland's Survey Research Center using a computer-assisted telephone interview instrument (CATI) to collect 24-h retrospective diaries and answers to a number of personal and exposure-related questions from each respondent. The resulting diary records contain beginning and ending times for each distinct combination of location and activity occurring on the diary day (i.e., each microenvironment). Between 340 and 1713 respondents of all ages were interviewed in each of the 10 EPA regions across the 48 contiguous states. Interviews were completed in 63% of the households contacted. NHAPS respondents reported spending an average of 87% of their time in enclosed buildings and about 6% of their time in enclosed vehicles. These proportions are fairly constant across the various regions of the U.S. and Canada and for the California population between the late 1980s, when the California Air Resources Board (CARB) sponsored a state-wide activity pattern study, and the mid-1990s, when NHAPS was conducted. However, the number of people exposed to environmental tobacco smoke (ETS) in California seems to have decreased over the same time period, where exposure is determined by the reported time spent with a smoker. In both California and the entire nation, the most time spent exposed to ETS was reported to take place in residential locations.
Ozone-induced formation of aldehydes was studied on the surface and in the gas phase above carpets and on carpet components. Samples of four carpets were exposed to 100 ppb ozone. Emission rates of aldehydes and other organic compounds were measured from exposed and unexposed samples. Surface interactions of ozone with carpets produced C1-C13 n-aldehydes and several unsaturated aldehydes. Total aldehyde emission rates increased markedly with ozone exposure, from 1 to 70 microg m(-2) h(-1) for unexposed samples, to 60-800 microg m(-2) h(-1) during exposure. One exposed sample emitted large amounts of 2-nonenal (180-230 microg m(-2) h(-1)), a compound with a low odor threshold. Material balance modeling of a residence with this high emitting carpet suggests (1) that the concentration of 2-nonenal would be well above its odor threshold even in areas with only moderate ambient ozone levels and (2) that odorous levels of 2-nonenal could persist for years. Reactions of ozone with gas-phase primary emissions from carpet significantly reduced the levels of 4-phenylcyclohexene and produced small amounts of branched ketones. Separately measured patterns of aldehyde emissions from ozone exposure of linseed and tung oils were similar but not identical to those observed from ozone-exposed carpets.
This paper reports effects of reactions between ozone and selected terpenes on the concentrations and size distributions of airborne particles in a typical indoor setting. The studies were conducted in adjacent, identical offices. In the first set of experiments, known concentrations of ozone and a selected terpene (either d-limonene, alpha-terpinene, or a terpene-based cleaner whose major constituent is alpha-pinene) were deliberately introduced into one of the offices while the other office served as a control. Subsequent particle formation and redistribution were monitored with an eight-channel optical particle counter. Particle formation was observed in each terpene system, but was greatest in the case of d-limonene. The number of particles in the 0.1-0.2 mu m diameter size range was as much as 20 times larger in the office with deliberately supplemented ozone and d-limonene than in the office serving as the control. The concentration differences in the larger size ranges developed with time, indicating the importance of coagulation and condensation processes in this indoor environment. In the second set of experiments, d-limonene was deliberately introduced into one of the offices. but ozone was not supplemented in either office; instead, the indoor ozone concentrations were those that happened to be present (primarily as a consequence of outdoor-to-indoor transport). In the office that contained supplemental d-limonene, the concentrations of the 0.1-0.2 mu m particles tracked those of indoor ozone (the limiting reagent) and were as much as 10 times greater than levels measured in the comparable office that did not contain supplemental d-limonene. The results demonstrate that ozone/terpene reactions can be a significant source of sub-micron particles in indoor settings, and further illustrate the potential for reactions among commonly occurring indoor pollutants to markedly influence indoor environments.
This study examines the influence of ventilation on chemical reactions among indoor pollutants. We have used a one compartment mass balance model to simulate unimolecular and bimolecular reactions occurring indoors. The initial modeling assumes steady-state conditions. However, at low air exchange rates, there may be insufficient time to achieve steady-state. Hence we have also modeled non steady-state scenarios. In the cases examined, the results demonstrate that the concentrations of products generated from reactions among indoor pollutants increase as the ventilation rate decreases. This is true for unimolecular and bimolecular reactions, regardless of whether the pollutants have indoor or outdoor sources. It is also true even when one of the pollutants has an outdoor concentration that displays large diurnal variations. We have supplemented the modeling studies with a series of experiments conducted in typical commercial offices. The reaction examined was that between ozone and limonene. The ozone was present as a consequence of outdoor-to-indoor transport while the limonene originated indoors. Results were obtained for low and high ventilation rates. Consistent with the modeling studies, the concentrations of monitored products were much larger at the lower ventilation rates (even though the ozone concentrations were lower). The potential for reactions among indoor pollutants to generate reactive and irritating products is an additional reason to maintain adequate ventilation in indoor environments.
Using an indirect technique to obtain a time-integrated signal, we have detected and quantified the hydroxyl radical (OH) in a commercial building. For the purpose of the measurements, the conditions in the office setting were manipulated, but they were representative of conditions that occur naturally. During monitoring periods when the concentrations of both ozone (O3) and d-limonene were elevated and the air exchange rate moderate, we found the average indoor OH concentration to be approximately 7 × 105 molecule/cm3. This value is lower than typical outdoor midday values (5 × 106 molecule/cm3) but larger than outdoor nighttime values. The results confirm that reactions among O3 and olefins can generate meaningful quantities of OH under conditions that commonly occur indoors. In turn, OH initiates a complex series of reactions that generate still other radicals and ultimately produce species that can adversely affect human health and artifacts in indoor environments.
Cited By (since 1996): 28
,
Export Date: 4 February 2013
,
Source: Scopus
, The following values have no corresponding Zotero field:
Author Address: UMDNJ-RW Johnson Medical School, Rutgers University, Environ./Occup. Hlth. Sci. Institute, Piscataway, NJ 08854, United States
Author Address: Intl. Ctr. for Indoor Environ./Ener., Technical University of Denmark, Lyngby DK, Denmark
Author Address: Telcordia Technology, Red Bank, NJ, United States
Ozone has been used as a germicidal agent for drinking water since 1903, and its activity in the aqueous phase is well documented. However, despite the wide use of ozone generators for indoor air treatment, there is little research data on ozone's biocidal activity in the gas phase. This article presents experimental data on the effect of ozone on both vegetative and spore-forming fungi as well as a spore-forming bacterium. Dried suspensions of the test organisms were exposed to a range of ozone concentrations from 3 to 10 ppm in 50-L Teflon-coated stainless steel chambers. A two-phase study was performed. The first phase was an extensive series of tests on the efficacy of ozone itself. Tests using organisms deposited on glass slides to minimize losses of ozone were carried out under conditions of high (90%) and low (30%) relative humidity (RH). For the organisms used in this study, ozone concentrations in the range of 6 to almost 10 ppm were required for significant kill. Organisms exposed under high RH conditions were generally more susceptible to ozone. The second phase of tests employed actual building materials as the test surfaces. No microbial kill was demonstrated on any of the building materials even at 9 ppm ozone.
In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2-1.4. This factor, which is an estimate of the average molecular weight per carbon weight for the organic aerosol, stems from very limited theoretical and laboratory studies conducted during the 1970s. This investigation suggests that 1.4 is the lowest reasonable estimate for the organic molecular weight per carbon weight for an urban aerosol and that 1.4 does not accurately represent the average organic molecular weight per carbon weight for a nonurban aerosol. Based on the current evaluation, ratios of 1.6 ± 0.2 for urban aerosols and 2.1 ± 0.2 for nonurban aerosols appear to be more accurate. Measurements are recommended. Literature values also suggest that 1.2 g/cm3 is a reasonable estimate for the organic aerosol density. This quantity is needed to convert between geometric and aerodynamic size distributions (e.g., to predict aerosol optical properties and understand cloud nucleating properties).
The purpose of this paper is to undertake a statistical analysis to specify empirical distributions and to estimate univariate parametric probability distributions for air exchange rates for residential structures in the United States. To achieve this goal, we used data compiled by the Brookhaven National Laboratory using a method known as the perfluorocarbon tracer (PFT) technique. While these data are not fully representative of all areas of the country or all housing types, they are judged to be by far the best available. The analysis is characterized by four key points: the use of data for 2,844 households; a four-region breakdown based on heating degree days, a best available measure of climatic factors affecting air exchange rates; estimation of lognormal distributions as well as provision of empirical (frequency) distributions; and provision of these distributions for all of the data, for the data segmented by the four regions, for the data segmented by the four seasons, and for the data segmented by a 16 region by season breakdown. Except in a few cases, primarily for small sample sizes, air exchange rates were found to be well fit by lognormal distributions (adjusted R2 0.95). The empirical or lognormal distributions may be used in indoor air models or as input variables for probabilistic human health risk assessments.
The airway irritation of (+)-α-pinene, ozone, mixtures thereof, and formaldehyde was evaluated by a mouse bioassay, in which sensory irritation, bronchoconstriction, and pulmonary irritation were measured. The effects are distinguished by analysis of the respiratory parameters. Significant sensory irritation (assessed from reduction of mean respiratory rate) was observed by dynamic exposure of the mice, over a period of 30 min, to a ca. 22 s old reaction mixture of ozone and (+)-α-pinene from a Teflon flow tube. The starting concentrations were 6 ppm and 80 ppm, respectively, which were diluted and let into the exposure chamber. About 10% ozone remained unreacted (0.4 ppm), <0.2 ppm formaldehyde, <0.4 ppm pinonaldehyde, <2 ppm formic acid, and <1 ppm acetic acid were formed. These concentrations, as well as that of the unreacted (+)-α-pinene (51 ppm), were below established no effect levels. The mean reduction of the respiratory rate (30%) was significantly different (p≪0.001) from clean air, as well as from exposure of (+)-α-pinene, ozone, and formaldehyde themselves at the concentrations measured. Addition of the effects of the measured residual reactants and products cannot explain the observed sensory irritation effect. This suggests that one or more strong airway irritants have been formed. Therefore, oxidation reactions of common naturally occurring unsaturated compounds (e.g., terpenes) may be relevant for indoor air quality.
Abstract Concentrations of volatile organic compounds (VOCs) measured indoors may exceed their odor thresholds, but are usually far below TLV estimates. Even applying additivity to eye and airway irritation effects, it is difficult to rationalize increased sick building syndrome (SBS) symptoms by exposure to generally chemically inert VOCs in the indoor environment.
Several studies suggest that chemical reactions in indoor air are linked with SBS symptoms and the examination of these reactions may be necessary in order to understand the role of VOCs as causative agents of SBS symptoms.
The usual evaluation of odor annoyance of VOCs based on odor thresholds should be modified, taking into account the large variation of individual human odor thresholds for single substances, and specific additivity phenomena even at subthreshold levels of VOCs.
The conclusion of this review is that chemical reactions between oxidizable VOCs and oxidants, such as ozone and possibly nitrogen oxides, can form irritants which may be responsible for the reported symptoms. Compounds adsorbed to particles may also contribute to SBS symptoms. The individual effects of indoor pollutants may act in concert with temperature and relative humidity. New analytical methods are required to measure the oxidative and reactive species or specific markers thereof in indoor air.
A comprehensive indoor particle characterization study was conducted in nine Boston-area homes in 1998 in order to characterize sources of PM in indoor environments. State-of-the-art sampling methodologies were used to obtain continuous PM2.5 concentration and size distribution particulate data for both indoor and outdoor air. Study homes, five of which were sampled during two seasons, were monitored over week-long periods. Among other data collected during the extensive monitoring efforts were 24-hr elemental/organic carbon (EC/OC) particulate data as well as semi-continuous air exchange rates and time-activity information. This rich data set shows that indoor particle events tend to be brief, intermittent, and highly variable, thus requiring the use of continuous instrumentation for their characterization. In addition to dramatically increasing indoor PM2.5 concentrations, these data demonstrate that indoor particle events can significantly alter the size distribution and composition of indoor particles. Source event data demonstrate that the impacts of indoor activities are especially pronounced in the ultrafine (d(a) ≤ 0.1 μm) and coarse (2.5 ≤ d(a) ≤ 10 μm) modes. Among the sources of ultrafine particles characterized in this study are indoor ozone/terpene reactions. Furthermore, EC/OC data suggest that organic carbon is a major constituent of particles emitted during indoor source events. Whether exposures to indoor-generated particles, particularly from large short-term peak events, may be associated with adverse health effects will become clearer when biological mechanisms are better known.
The airway irritation of a reaction mixture of R-(+)-limonene and ozone was evaluated by a mouse bioassay in which sensory irritation, bronchoconstriction and pulmonary irritation were measured. Significant sensory irritation (33% reduction of mean respiratory rate) was observed by dynamic exposure of the mice, during 30 min, to a ca. 16 s old reaction mixture of ozone and limonene. The initial concentrations were nominally 4 ppm O3 and 48 ppm limonene. After reaction, the residual O3 was <0.03 ppm. Conventional analytical chemical methods were used to measure the formation of readily identified and stable products. Besides the expected products, 1-methyl-4-acetylcyclohexene (AMCH), 3-isopropenyl-6-oxoheptanal (IPOH), formaldehyde and formic acid, autooxidation products of limonene and a series of compounds (i.e., acetone, acrolein and acetic acid), which may or may not be artefacts, were identified. Addition of the sensory irritation effects of the residual reactants and all the identified compounds could not explain the observed sensory irritation effect. This suggests that one or more strong airway irritants were formed. Since limonene is common in the indoor air, and ozone is infiltrated from outdoors and/or produced indoors (e.g., by photocopiers), such oxidation reactions may be relevant for indoor air quality.
As air infiltrates through unintentional openings in building envelopes, pollutants may interact with adjacent surfaces. Such interactions can alter human exposure to air pollutants of outdoor origin. We present modeling explorations of the proportion of particles and reactive gases (e.g., ozone) that penetrate building envelopes as air enters through cracks and wall cavities. Calculations were performed for idealized rectangular cracks, assuming regular geometry, smooth inner crack surface and steady airflow. Particles of 0.1–1.0 μm diameter are predicted to have the highest penetration efficiency, nearly unity for crack heights of 0.25 mm or larger, assuming a pressure difference of 4 Pa or greater and a flow path length of 3 cm or less. Supermicron and ultrafine particles are significantly removed by means of gravitational settling and Brownian diffusion, respectively. In addition to crack geometry, ozone penetration depends on its reactivity with crack surfaces, as parameterized by the reaction probability. For reaction probabilities less than ∼10−5, penetration is complete for cracks heights greater than ∼1 mm. However, penetration through mm scale cracks is small if the reaction probability is ∼10−4 or greater. For wall cavities, fiberglass insulation is an efficient particle filter, but particles would penetrate efficiently through uninsulated wall cavities or through insulated cavities with significant airflow bypass. The ozone reaction probability on fiberglass fibers was measured to be 10−7 for fibers previously exposed to high ozone levels and 6×10−6 for unexposed fibers. Over this range, ozone penetration through fiberglass insulation would vary from >90% to ∼10–40%. Thus, under many conditions penetration is high; however, there are realistic circumstances in which building envelopes can provide substantial pollutant removal. Not enough is yet known about the detailed nature of pollutant penetration leakage paths to reliably predict infiltration into real buildings.
Experiments were conducted in an 11 m3 environmental chamber to investigate secondary particles resulting from homogeneous reactions between ozone and α-pinene. Experimental results indicate that rapid fine particle growth occurs due to homogeneous reactions between ozone and α-pinene, and subsequent gas-to-particle partitioning of the products. A new indoor air quality model was used to predict dynamic particle mass concentrations based on detailed homogeneous chemical mechanisms and partitioning of semi-volatile products to particles. Chamber particle mass concentrations were estimated from measured particle size distributions and were in reasonable agreement with results predicted from the model. Both experimental and model results indicate that secondary particle mass concentrations increase substantially with lower air exchange rates. This is an interesting result, given a continuing trend toward more energy-efficient buildings. Secondary particle mass concentrations are also predicted to increase with lower indoor temperatures, higher outdoor ozone concentrations, higher outdoor particle concentrations, and higher indoor α-pinene emissions rates.
The products of the gas-phase reactions of O-3 with 1-pentene, 1-hexene, 1-heptene, 1-octene, 2,3-dimethyl-1-butene, cyclopentene, and 1-methylcyclohexene have been investigated at room temperature and 740 Torr total pressure of air in the presence of cyclohexane or n-octane to scavenge OH radicals. Products were identified and quantified by gas chromatography and in situ Fourier transform infrared absorption spectroscopy. In the presence of cyclo-hexane, cyclohexanone and cyclohexanol were observed as products, showing the formation of OH radicals from these O-3 reactions. The OH radical formation yields derived were as follows: 1-pentene, 0.37; 1-hexene, 0.32; 1-heptene, 0.27; 1-octene, 0.18; 2,3-dimethyl-1-butene, 0.50; cyclopentene, 0.61; and 1-methylcyclohexene, 0.90, all with estimated overall uncertainties of a factor of similar to 1.5. The carbonyl products identified and quantified were as follows: from 1-pentene: butanal, 0.541 +/- 0.065, and HCHO, 0.595 +/- 0.055; from 1-hexene: pentanal, 0.518 +/- 0.095, and HCHO, 0.575 +/- 0.057; from 1-heptene: hexanal, 0.582 +/- 0.078, and HCHO, 0.533 +/- 0.049; from 1-octene: heptanal, 0.527 +/- 0.070, and HCHO, 0.519 +/- 0.054; from 2,3-dimethyl-1-butene: 3-methyl-2-butanone, 0.391 +/- 0.050, and HCHO, 0.776 +/- 0.071; from cyclopentene: butanal, 0.195 +/- 0.027; and from 1-methylcyclohexene: 5-acetylpentanal, 0.100 +/- 0.024. For the 1-alkenes, the sum of the two carbonyl products expected from the decomposition of the initially formed primary ozonide is 1.1 +/- 0.1, consistent with the presently believed reaction mechanism. The 3-methyl-2-butanone and HCHO yields from 2,3-dimethyl-1-butene show that the primary ozonide decomposes preferentially to HCHO plus the dialkyl-substituted [(CH3)(2)CHC(CH3)OO]* biradical rather than to 3-methyl-2-butanoneplus the [CH2OO]* biradical.
In urban and suburban settings, indoor ozone exposures can represent a significant fraction of an individual's total exposure. The decay rate, one of the factors determining indoor ozone concentrations, is inadequately understood in residences. Decay rates were calculated by introducing outdoor air containing 80-160 parts per billion ozone into 43 residences and monitoring the reduction in indoor concentration as a function of time. The mean decay rate measured in the living rooms of 43 Southern California homes was 2.80 +/- 1.30 hr-1, with an average ozone deposition velocity of 0.049 +/- 0.017 cm/sec. The experimental protocol was evaluated for precision by repeating measurements in one residence on five different days, collecting 44 same-day replicate measurements, and by simultaneous measurements at two locations in six homes. Measured decay rates were significantly correlated with house type and the number of bedrooms. The observed decay rates were higher in multiple-family homes and homes with fewer than three bedrooms. Homes with higher surface-area-to-volume ratios had higher decay rates. The ratio of indoor-to-outdoor ozone concentrations in homes not using air conditioning and open windows was 68 +/- 18%, while the ratio of indoor-to-outdoor ozone was less than 10% for the homes with air conditioning in use.
Room ozonization has been in widespread use to "freshen" indoor air for more than 100 years. This use is sometimes promoted with the claim that ozone can oxidize airborne gases, and even particulates, to simple carbon dioxide and water vapor. Aside from whether ozone can improve indoor air quality, the potentially deleterious consequences to public health of overexposure to ozone are of concern. The literature on both allegations is reviewed. It indicates that ozone is not a practical and effective means of improving indoor air quality, especially in light of its potentially serious risk to health.
Population subsets whose behavior leads to unusually large exposures to toxicants are of interest to exposure assessors. Despite U.S. Food and Drug Administration (FDA) restriction since 1974, ozone generating devices continue to be marketed in the U.S. for indoor use. Promotional materials cite a host of alleged benefits to indoor environmental quality. Generation rates cited in sales literature are used here to estimate indoor air ozone concentrations that could result from use of such equipment. Predictions exceed relevant air quality standards, in some cases by a substantial margin. Limited available experimental measurements support this finding.
A comprehensive indoor particle characterization study was conducted in nine Boston-area homes in 1998 in order to characterize sources of PM in indoor environments. State-of-the-art sampling methodologies were used to obtain continuous PM2.5 concentration and size distribution particulate data for both indoor and outdoor air. Study homes, five of which were sampled during two seasons, were monitored over week-long periods. Among other data collected during the extensive monitoring efforts were 24-hr elemental/organic carbon (EC/OC) particulate data as well as semi-continuous air exchange rates and time-activity information. This rich data set shows that indoor particle events tend to be brief, intermittent, and highly variable, thus requiring the use of continuous instrumentation for their characterization. In addition to dramatically increasing indoor PM2.5 concentrations, these data demonstrate that indoor particle events can significantly alter the size distribution and composition of indoor particles. Source event data demonstrate that the impacts of indoor activities are especially pronounced in the ultrafine (da < or = 0.1 micron) and coarse (2.5 < or = da < or = 10 microns) modes. Among the sources of ultrafine particles characterized in this study are indoor ozone/terpene reactions. Furthermore, EC/OC data suggest that organic carbon is a major constituent of particles emitted during indoor source events. Whether exposures to indoor-generated particles, particularly from large short-term peak events, may be associated with adverse health effects will become clearer when biological mechanisms are better known.
The concentration of indoor ozone depends on a number of factors, including the outdoor ozone concentration, air exchange rates, indoor emission rates, surface removal rates, and reactions between ozone and other chemicals in the air. Outdoor ozone concentrations often display strong diurnal variations, and this adds a dynamic excitation to the transport and chemical mechanisms at play. Hence, indoor ozone concentrations can vary significantly from hour-to-hour, day-to-day, and season-to-season, as well as from room-to-room and structure-to-structure. Under normal conditions, the half-life of ozone indoors is between 7 and 10 min and is determined primarily by surface removal and air exchange. Although reactions between ozone and most other indoor pollutants are thermodynamically favorable, in the majority of cases they are quite slow. Rate constants for reactions of ozone with the more commonly identified indoor pollutants are summarized in this article. They show that only a small fraction of the reactions occur at a rate fast enough to compete with air exchange, assuming typical indoor ozone concentrations. In the case of organic compounds, the "fast" reactions involve compounds with unsaturated carbon-carbon bonds. Although such compounds typically comprise less than 10% of indoor pollutants, their reactions with ozone have the potential to be quite significant as sources of indoor free radicals and multifunctional (-C=O, -COOH, -OH) stable compounds that are often quite odorous. The stable compounds are present as both gas phase and condensed phase species, with the latter contributing to the overall concentration of indoor submicron particles. Indeed, ozone/alkene reactions provide a link between outdoor ozone, outdoor particles and indoor particles. Indoor ozone and the products derived from reactions initiated by indoor ozone are potentially damaging to both human health and materials; more detailed explication of these impacts is an area of active investigation.
This study examines the primary and secondary products resulting from reactions initiated by adding ozone to complex mixtures of volatile organic compounds (VOC). The mixtures were representative of organic species typically found indoors, but the concentrations tended to be higher than normal indoor levels. Each 4-h experiment was conducted in a controlled environmental facility (CEF, 25 m3) ventilated at approximately 1.8 h(-1). The mixture investigated included 23 VOC (no O3), O3/23 VOC, O3/21 VOC (no d-limonene or alpha-pinene), and O3/terpene only (d-limonene and alpha-pinene). The net O3 concentration was approximately 40 ppb in each experiment, and the total organic concentration was 26 mg/m3 for the 23 VOC mixture, 25 mg/m3 for the 21 VOC mixture, and 1.7 mg/m3 for the d-limonene and alpha-pinene mixture. When the 23 VOC were added to the CEF containing no O3, no compounds other than those deliberately introduced were observed. When O3 was added to the CEF containing the 23 VOC mixture, both gas and condensed phase products were found, including aldehydes, organic acids, and submicron particles (140 microg/m3). When O3 was added to the CEF containing the 21 VOC without the two terpenes (O3/21 VOC condition), most of the products that were observed in the O3/23 VOC experiments were no longer present or present at much lower concentrations. Furthermore, the particle mass concentration was 2-7 microg/m3, indistinguishable from the background particle concentration level. When O3 was added to the CEF containing only two terpenes, the results were similar to those in the O3/23 VOC experiments, but the particle mass concentration (190 microg/m3) was higher. The results indicate that (i) O3 reacts with unsaturated alkenes under indoor conditions to generate submicron particles and other potentially irritating species, such as aldehydes and organic acids; (ii) the major chemical transformations that occurred under our experimental conditions were driven by O3/d-limonene and O3/alpha-pinene reactions; and (iii) the hydroxyl radicals (OH) that were generated from the O3/terpene reactions played an important role in the chemical transformations and were responsible for approximately 56-70% of the formaldehyde, almost all of the p-tolualdehyde, and 19-29% of the particle mass generated in these experiments.
Ozone and limonene in indoor air: a source of submicron particle exposure
- Wainman