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The hydroxyl radical (OH) in indoor air: Sources and implications
Atmospheric Environment 99 (2014) 568e570
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
The hydroxyl radical (OH) in indoor air: Sources and implications Considering that people spend on average 80e90% of their life indoors, indoor air quality is of major importance for human health. In addition to specific indoor sources and entrainment from the outside atmosphere, harmful pollutants can be also formed indoors by in-situ secondary chemistry. While the first two processes have been well studied in the past, our understanding of indoor oxidation processes is still in its infancy compared to the ambient atmosphere. Oxidation of gaseous trace species is initiated by direct photolysis, ozonolysis and attack by nitrate (NO3) and hydroxyl (OH) radicals. The OH radical is the most powerful oxidant, controlling the self cleaning capacity of the atmosphere by inducing radical chain reactions which consequently remove atmospheric pollutants. However, a number of harmful intermediates, e.g. ozone (O3), can also be formed during these reactions. The main initiation sources of OH in the atmosphere are the photolysis of O3 and nitrous acid (HONO) and the ozonolysis of alkenes. In contrast to the ambient atmosphere, scientists do not fully understand the indoor OH sources and consequently the associated implications for indoor air quality and human health. 1. Current state of knowledge The analysis presented by Nazaroff and Cass (1989) suggest that due to the attenuation of UV radiation, the indoor hydroxyl radical production rates from photolytic processes are less important than those resulting from the reactions of ozone with alkenes (Weschler and Shields, 1996). Chemical models and indirect measurements considering the ozonolysis of alkenes as the most important OH source suggest indoor concentrations of OH radicals in the order of only 104 up to a few times 105 cm3 under realistic indoor settings (Carslaw, 2007) limited by the typical low indoor O3 levels. Carslaw (2007) assumes a minor contribution of 12% of HONO photolysis to the total production of OH radicals in indoor environments as compared to the 88% attributed to the ozonolysis of alkenes/monoterpenes (O3 þ A/MTs). Only considering extremely high actinic flux levels predicted OH concentration of 1.3 $ 106 cm3. In addition, the HONO levels in the model by Carslaw (2007) were quite low based on reactive uptake kinetics for NO2 to HONO conversion of 106 ca. one order of magnitude lower than the one exhibited by photosensitized heterogeneous re mez actions (Stemmler et al., 2006; Gandolfo et al., 2014). Since Go Alvarez et al. (2014) found that the indoor OH was mainly caused by HONO photolysis, such models will not be able to describe correctly indoor OH levels. Despite the model findings, there are two major reasons why also HONO should be considered as an important indoor OH source. First, in contrast to other photochemical OH sources, HONO has http://dx.doi.org/10.1016/j.atmosenv.2014.10.031 1352-2310/© 2014 Elsevier Ltd. All rights reserved.
strong absorption bands in the near-UV region extending up to ~390 nm, for which reasonable UV light intensity is available in mez Alvarez et al., 2013). Second, significant emissions doors (Go and strong heterogeneous indoor sources can result in HONO levels up to an order of magnitude higher than those in the ambient atmosphere (Brauer et al., 1990). Indeed, in the indoor settings not only the concentration of the most important precursor NO2 is higher (Monn, 2001), but also the surface to volume ratio (S/V) available for heterogeneous formation and therefore, the potential for HONO production is significantly elevated. For example, in industrial workplaces and homes equipped with gas stoves or when burning candles, peak NO2 mixing ratios may reach up to 2 ppm with a 24-h average NO2 mixing ratio of up to 500 ppb (Monn, 2001). Caused by these high precursor levels, HONO concentrations of up to 30 ppb were measured indoors (Febo and Perrino, 1995). A recent campaign carried out in a school-classroom situated in the centre of a typical metropolitan area revealed that the level of OH radicals depends strongly on the intensity of the near-UV sun mez Alvarez et al., light, which penetrates through the windows (Go 2013). These measurements employing the sensitive in-situ LIFFAGE technique (Laser-Induced Fluorescence using the Fluorescence Assay by Gas Expansion) revealed unexpectedly high OH concentrations of up to ~2 $ 106 cm3 even for low indoor UV light intensities. These high OH levels, do not differ significantly from those observed in the ambient atmosphere (Stone et al., 2012). Additionally, measurements from this campaign showed that OH radical levels were linearly correlated with the product of the photolysis frequency of HONO (J(HONO)) and its concentration. As a major conclusion, the photolysis of HONO was proposed to represent the main source of OH radicals indoors. 2. Future perspectives mez Alvarez et al., The results from the pioneering study (Go 2013) suggest several directions for future investigations on indoor air chemistry: In order to properly understand indoor photochemistry the spectrally resolved solar actinic flux should be assessed in a variety of indoor environments. Although significantly altered by shadowing and window absorption, particularly in the UV region, the degree of sunlight attenuation indoors is highly variable and depends on the geographic location, the time of year, orientation of the room, size of the windows and type of window glass. The photochemical model by Carslaw (2007) indicated that the spectral and intensity characteristics of the light could have strong impact on the indoor OH radical production rates (up to a factor of three) from HONO photolysis.
S. Gligorovski et al. / Atmospheric Environment 99 (2014) 568e570
Unfortunately, there are currently no studies available in which the spectrally resolved actinic flux was quantified indoors. As the architectural trend of new modern habitation tends towards houses with larger windows and glass-wall towers, the indoor photochemistry will become increasingly more important in the future. OH radical concentrations should be studied for different indoor environments. Here, indirect measurements using tracer methods, which can provide average indoor OH concentrations (Weschler and Shields, 1996), should be combined with direct mez Alvarez et al., 2013). in-situ techniques, e.g. LIF-FAGE (Go This combination of measurements will provide a clearer picture on indoor OH levels. HONO should be measured regularly in indoor studies to understand its contribution to the sources of the OH radical. Gligorovski and Weschler (2013) stated that investigators should consider indoor deployment of state-of-the-art analytical methods that have been used to detect outdoor pollutants in addition to developing techniques specifically adapted to indoor environments. In this context, selective and sensitive HONO measurements would be also of importance in medical studies due to the adverse health effects of HONO (Pitts, 1983; Shapiro et al., 1977; Shapley, 1976). For example, the heterogeneous reaction of HONO with surface deposited nicotine from tobacco smoke, known as third hand smoke, lead to formation of nitrosamines (Sleiman et al., 2010). The mechanisms leading to HONO formation still constitute a field were significant uncertainties remain. Therefore, special focus should be on “new” photosensitized reactions (George mez Alvarez et al., 2014) et al., 2005; Stemmler et al., 2006; Go on different indoor surfaces (Fig. 1). A better understanding of these reactions may help to explain the high HONO levels observed indoors during daytime, which cannot be explained by slow dark reactions used in former indoor models (e.g. Carslaw, 2007). In order to properly understand the mechanistic processes the photosensitized heterogeneous reactions of NO2 towards real indoor surfaces like detergent, paint, carpet, wood have to be assessed besides the reactions on pure organic compounds which were used as a proxy for real surface. This would mark a significant break-away from most traditional studies that have focused only on model compounds leading to
569
some problems with respect to the quantitative understanding of such processes. The comprehensive understanding of HONO chemistry indoors is essential for the photochemical models in order to properly predict the HONO levels in enclosed environments. Especially, the “new” photochemical formation processes of indoor HONO should be implemented in the models to account for the missing daytime HONO sources and to predict reasonable OH radical levels and the mez Alvarez et al. corresponding radical chemistry. Recently, Go (2014) and Bartolomei et al. (2014) have discovered new light mediated HONO sources, occurring on household surfaces covered by detergent, lacquer, paint, etc. Remarkably the amount of HONO produced by these sources is of similar magnitude to that reported in some recent landmark studies (e.g. Stemmler et al., 2006) involving the heterogeneous reactions of NO2 on outdoor surfaces such as organic aerosols and soil. These results prove that indoor surfaces are not only physical but also photochemical substrates that play an active role in the enhancement of the generation of HONO indoors. Gandolfo et al. (2014) for instance, revealed that the geometric NO2 uptake coefficient (g) can reach values of up to 1.6 $ 105 upon light irradiation of a photocatalytic indoor paint yielding about 15% of HONO. Measurements as outlined above would significantly improve our understanding of indoor oxidation processes and their implications on human health. This area of research has strong social repercussions as the depletion of fossil fuel resources linked to climate change forces us to reduce our energy consumption. During the last twenty years the design and construction of buildings has been radically altered to improve the buildings' energy efficiency in order to lower running costs. The new building advances have resulted in more airtight modern home environments, offices, schools and hospitals. Although these improvements have led to lower running energy costs, they could also result in higher levels of air pollutants than outdoors. As a consequence, indoor air could contain chronic, unhealthy concenmez Alvarez et al. (2013) trations of pollutants. The findings by Go suggest that a re-evaluation of our knowledge about indoor OH radical chemistry is necessary. High levels of OH radicals introduced into such a soup of pollutants could induce chemical reactions that produce traditionally not considered species with additional adverse health effects, and the consequences of this remain to be explored. Scientists have not yet studied in detail
Fig. 1. Simplified illustration highlighting the most important generation pathways of HONO and OH radicals indoors. Image courtesy of Vladimir Gligorovski (Ecole Nationale rieure d’Architecture de Marseille). Supe
570
S. Gligorovski et al. / Atmospheric Environment 99 (2014) 568e570
the impact of OH radical chemistry indoors, so its role towards the human health is unclear. References €rgel, M., Gligorovski, S., Alvarez, E.G., Gandolfo, A., Strekowski, R., Bartolomei, V., So Quivet, E., Held, A., Zetzsch, C., Wortham, H., 2014. Formation of indoor nitrous acid (HONO) by light-induced NO2 heterogeneous reactions with white wall paint. Environ. Sci. Pollut. Res. 21, 9259e9269. Brauer, M., Ryan, P.B., Suh, H.H., Koutrakis, P., Spengler, J.D., Leslie, N.P., Billick, I.H., 1990. Measurements of nitrous acid inside two research houses. Environ. Sci. Technol. 24, 1521e1527. Carslaw, N., 2007. A new detailed chemical model for indoor air pollution. Atmos. Environ. 41, 1164e1179. Febo, A., Perrino, C., 1995. Measurement of high concentration of nitrous acid inside automobiles. Atmos. Environ. 29, 345e351. Gandolfo, A., Bartolomei, V., Gomez Alvarez, E., Gligorovski, S., Kleffmann, J., Wortham, H., 2014. The impact of photocatalytic paints on indoor NOx and HONO levels. Appl. Catal. B Environ.. George, C., Strekowski, R.S., Kleffmann, J., Stemmler, K., Ammann, M., 2005. Photoenhanced uptake of gaseous NO2 on solid organic compounds: a photochemical source of HONO? Faraday Discuss. 130, 195e210. Gligorovski, S., Weschler, C.J., 2013. The oxidative capacity of indoor atmospheres. Environ. Sci. Technol. 47 (24), 13905e13906. mez Alvarez, E., Amedro, D., Afif, C., Gligorovski, S., Schoemacker, C., Fittschen, C., Go Doussin, J.-F., Wortham, H., 2013. Photolysis of nitrous acid as a primary source of OH radicals indoors. Proc. Natl. Acad. Sci. U. S. A. 33, 13294e13299. mez Alvarez, E., So €rgel, M., Gligorovski, S., Bassil, S., Bartolomei, V., Coulomb, B., Go Zetzsch, C., Wortham, H., 2014. Light-induced nitrous acid (HONO) production from NO2 heterogeneous reactions on household chemicals. Atmos. Environ. 95, 391e399. Monn, C., 2001. Exposure assessment of air pollutants: a review on spatial heterogeneity and indoor/outdoor/personal exposure to suspended particulate matter, nitrogen dioxide and ozone. Atmos. Environ. 35, 1e32. Nazaroff, W.W., Cass, G.R., 1989. Mathematical modeling of chemically reactive pollutants in indoor air. Environ. Sci. Technol. 23, 157e166. Pitts Jr., J.N., 1983. Formation and fate of gaseous and particulate mutagens and carcinogens in real and simulated atmospheres. Environ. Health Perspect. 47, 115e140.
Shapley, D., 1976. Nitrosamines: scientists on the trail of prime suspect in urban cancer. Science 191, 268e270. Shapiro, R., Dubelman, S., Feinberg, A.M., Crain, P.F., McCloskey, J.A., 1977. Isolation and identification of cross-linked nucleosides from nitrous acid treated deoxyribonucleic acid. J. Am. Chem. Soc. 99, 302e303. Sleiman, M., Gundel, L.A., Pankow, J.F., Jacob, P., Singer, B.C., Destaillats, H., 2010. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smokehazards. Proc. Natl. Acad. Sci. U. S. A. 107, 6576e6581. Stemmler, K., Ammann, M., Donders, C., Kleffmann, J., George, C., 2006. Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid. Nat. Chem. 440, 195e198. Stone, D., Whalley, K.L., Heard, E.D., 2012. Tropospheric OH and HO2 radicals: field measurements and model comparisons. Chem. Soc. Rev. 41 (19), 6348e6404. Weschler, C.J., Shields, H.C., 1996. Production of the hydroxyl radical in indoor air. Environ. Sci. Technol. 30, 3250e3258.
Sasho Gligorovski*, Henri Wortham Aix Marseille University, CNRS, Laboratoire de Chimie de l'Environnement (FRE 3416), (Case 29), 3 Place Victor Hugo, F e 13331 Marseille Cedex 3, France € rg Kleffmann Jo €t Wuppertal, Gaußstr. Physikalische Chemie/FB C, Bergische Universita 20, 42119 Wuppertal, Germany E-mail address: [email protected]. * Corresponding author. E-mail address: [email protected] (S. Gligorovski).
25 July 2014 Available online 16 October 2014
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
The hydroxyl radical (OH) in indoor air: Sources and implications Considering that people spend on average 80e90% of their life indoors, indoor air quality is of major importance for human health. In addition to specific indoor sources and entrainment from the outside atmosphere, harmful pollutants can be also formed indoors by in-situ secondary chemistry. While the first two processes have been well studied in the past, our understanding of indoor oxidation processes is still in its infancy compared to the ambient atmosphere. Oxidation of gaseous trace species is initiated by direct photolysis, ozonolysis and attack by nitrate (NO3) and hydroxyl (OH) radicals. The OH radical is the most powerful oxidant, controlling the self cleaning capacity of the atmosphere by inducing radical chain reactions which consequently remove atmospheric pollutants. However, a number of harmful intermediates, e.g. ozone (O3), can also be formed during these reactions. The main initiation sources of OH in the atmosphere are the photolysis of O3 and nitrous acid (HONO) and the ozonolysis of alkenes. In contrast to the ambient atmosphere, scientists do not fully understand the indoor OH sources and consequently the associated implications for indoor air quality and human health. 1. Current state of knowledge The analysis presented by Nazaroff and Cass (1989) suggest that due to the attenuation of UV radiation, the indoor hydroxyl radical production rates from photolytic processes are less important than those resulting from the reactions of ozone with alkenes (Weschler and Shields, 1996). Chemical models and indirect measurements considering the ozonolysis of alkenes as the most important OH source suggest indoor concentrations of OH radicals in the order of only 104 up to a few times 105 cm3 under realistic indoor settings (Carslaw, 2007) limited by the typical low indoor O3 levels. Carslaw (2007) assumes a minor contribution of 12% of HONO photolysis to the total production of OH radicals in indoor environments as compared to the 88% attributed to the ozonolysis of alkenes/monoterpenes (O3 þ A/MTs). Only considering extremely high actinic flux levels predicted OH concentration of 1.3 $ 106 cm3. In addition, the HONO levels in the model by Carslaw (2007) were quite low based on reactive uptake kinetics for NO2 to HONO conversion of 106 ca. one order of magnitude lower than the one exhibited by photosensitized heterogeneous re mez actions (Stemmler et al., 2006; Gandolfo et al., 2014). Since Go Alvarez et al. (2014) found that the indoor OH was mainly caused by HONO photolysis, such models will not be able to describe correctly indoor OH levels. Despite the model findings, there are two major reasons why also HONO should be considered as an important indoor OH source. First, in contrast to other photochemical OH sources, HONO has http://dx.doi.org/10.1016/j.atmosenv.2014.10.031 1352-2310/© 2014 Elsevier Ltd. All rights reserved.
strong absorption bands in the near-UV region extending up to ~390 nm, for which reasonable UV light intensity is available in mez Alvarez et al., 2013). Second, significant emissions doors (Go and strong heterogeneous indoor sources can result in HONO levels up to an order of magnitude higher than those in the ambient atmosphere (Brauer et al., 1990). Indeed, in the indoor settings not only the concentration of the most important precursor NO2 is higher (Monn, 2001), but also the surface to volume ratio (S/V) available for heterogeneous formation and therefore, the potential for HONO production is significantly elevated. For example, in industrial workplaces and homes equipped with gas stoves or when burning candles, peak NO2 mixing ratios may reach up to 2 ppm with a 24-h average NO2 mixing ratio of up to 500 ppb (Monn, 2001). Caused by these high precursor levels, HONO concentrations of up to 30 ppb were measured indoors (Febo and Perrino, 1995). A recent campaign carried out in a school-classroom situated in the centre of a typical metropolitan area revealed that the level of OH radicals depends strongly on the intensity of the near-UV sun mez Alvarez et al., light, which penetrates through the windows (Go 2013). These measurements employing the sensitive in-situ LIFFAGE technique (Laser-Induced Fluorescence using the Fluorescence Assay by Gas Expansion) revealed unexpectedly high OH concentrations of up to ~2 $ 106 cm3 even for low indoor UV light intensities. These high OH levels, do not differ significantly from those observed in the ambient atmosphere (Stone et al., 2012). Additionally, measurements from this campaign showed that OH radical levels were linearly correlated with the product of the photolysis frequency of HONO (J(HONO)) and its concentration. As a major conclusion, the photolysis of HONO was proposed to represent the main source of OH radicals indoors. 2. Future perspectives mez Alvarez et al., The results from the pioneering study (Go 2013) suggest several directions for future investigations on indoor air chemistry: In order to properly understand indoor photochemistry the spectrally resolved solar actinic flux should be assessed in a variety of indoor environments. Although significantly altered by shadowing and window absorption, particularly in the UV region, the degree of sunlight attenuation indoors is highly variable and depends on the geographic location, the time of year, orientation of the room, size of the windows and type of window glass. The photochemical model by Carslaw (2007) indicated that the spectral and intensity characteristics of the light could have strong impact on the indoor OH radical production rates (up to a factor of three) from HONO photolysis.
S. Gligorovski et al. / Atmospheric Environment 99 (2014) 568e570
Unfortunately, there are currently no studies available in which the spectrally resolved actinic flux was quantified indoors. As the architectural trend of new modern habitation tends towards houses with larger windows and glass-wall towers, the indoor photochemistry will become increasingly more important in the future. OH radical concentrations should be studied for different indoor environments. Here, indirect measurements using tracer methods, which can provide average indoor OH concentrations (Weschler and Shields, 1996), should be combined with direct mez Alvarez et al., 2013). in-situ techniques, e.g. LIF-FAGE (Go This combination of measurements will provide a clearer picture on indoor OH levels. HONO should be measured regularly in indoor studies to understand its contribution to the sources of the OH radical. Gligorovski and Weschler (2013) stated that investigators should consider indoor deployment of state-of-the-art analytical methods that have been used to detect outdoor pollutants in addition to developing techniques specifically adapted to indoor environments. In this context, selective and sensitive HONO measurements would be also of importance in medical studies due to the adverse health effects of HONO (Pitts, 1983; Shapiro et al., 1977; Shapley, 1976). For example, the heterogeneous reaction of HONO with surface deposited nicotine from tobacco smoke, known as third hand smoke, lead to formation of nitrosamines (Sleiman et al., 2010). The mechanisms leading to HONO formation still constitute a field were significant uncertainties remain. Therefore, special focus should be on “new” photosensitized reactions (George mez Alvarez et al., 2014) et al., 2005; Stemmler et al., 2006; Go on different indoor surfaces (Fig. 1). A better understanding of these reactions may help to explain the high HONO levels observed indoors during daytime, which cannot be explained by slow dark reactions used in former indoor models (e.g. Carslaw, 2007). In order to properly understand the mechanistic processes the photosensitized heterogeneous reactions of NO2 towards real indoor surfaces like detergent, paint, carpet, wood have to be assessed besides the reactions on pure organic compounds which were used as a proxy for real surface. This would mark a significant break-away from most traditional studies that have focused only on model compounds leading to
569
some problems with respect to the quantitative understanding of such processes. The comprehensive understanding of HONO chemistry indoors is essential for the photochemical models in order to properly predict the HONO levels in enclosed environments. Especially, the “new” photochemical formation processes of indoor HONO should be implemented in the models to account for the missing daytime HONO sources and to predict reasonable OH radical levels and the mez Alvarez et al. corresponding radical chemistry. Recently, Go (2014) and Bartolomei et al. (2014) have discovered new light mediated HONO sources, occurring on household surfaces covered by detergent, lacquer, paint, etc. Remarkably the amount of HONO produced by these sources is of similar magnitude to that reported in some recent landmark studies (e.g. Stemmler et al., 2006) involving the heterogeneous reactions of NO2 on outdoor surfaces such as organic aerosols and soil. These results prove that indoor surfaces are not only physical but also photochemical substrates that play an active role in the enhancement of the generation of HONO indoors. Gandolfo et al. (2014) for instance, revealed that the geometric NO2 uptake coefficient (g) can reach values of up to 1.6 $ 105 upon light irradiation of a photocatalytic indoor paint yielding about 15% of HONO. Measurements as outlined above would significantly improve our understanding of indoor oxidation processes and their implications on human health. This area of research has strong social repercussions as the depletion of fossil fuel resources linked to climate change forces us to reduce our energy consumption. During the last twenty years the design and construction of buildings has been radically altered to improve the buildings' energy efficiency in order to lower running costs. The new building advances have resulted in more airtight modern home environments, offices, schools and hospitals. Although these improvements have led to lower running energy costs, they could also result in higher levels of air pollutants than outdoors. As a consequence, indoor air could contain chronic, unhealthy concenmez Alvarez et al. (2013) trations of pollutants. The findings by Go suggest that a re-evaluation of our knowledge about indoor OH radical chemistry is necessary. High levels of OH radicals introduced into such a soup of pollutants could induce chemical reactions that produce traditionally not considered species with additional adverse health effects, and the consequences of this remain to be explored. Scientists have not yet studied in detail
Fig. 1. Simplified illustration highlighting the most important generation pathways of HONO and OH radicals indoors. Image courtesy of Vladimir Gligorovski (Ecole Nationale rieure d’Architecture de Marseille). Supe
570
S. Gligorovski et al. / Atmospheric Environment 99 (2014) 568e570
the impact of OH radical chemistry indoors, so its role towards the human health is unclear. References €rgel, M., Gligorovski, S., Alvarez, E.G., Gandolfo, A., Strekowski, R., Bartolomei, V., So Quivet, E., Held, A., Zetzsch, C., Wortham, H., 2014. Formation of indoor nitrous acid (HONO) by light-induced NO2 heterogeneous reactions with white wall paint. Environ. Sci. Pollut. Res. 21, 9259e9269. Brauer, M., Ryan, P.B., Suh, H.H., Koutrakis, P., Spengler, J.D., Leslie, N.P., Billick, I.H., 1990. Measurements of nitrous acid inside two research houses. Environ. Sci. Technol. 24, 1521e1527. Carslaw, N., 2007. A new detailed chemical model for indoor air pollution. Atmos. Environ. 41, 1164e1179. Febo, A., Perrino, C., 1995. Measurement of high concentration of nitrous acid inside automobiles. Atmos. Environ. 29, 345e351. Gandolfo, A., Bartolomei, V., Gomez Alvarez, E., Gligorovski, S., Kleffmann, J., Wortham, H., 2014. The impact of photocatalytic paints on indoor NOx and HONO levels. Appl. Catal. B Environ.. George, C., Strekowski, R.S., Kleffmann, J., Stemmler, K., Ammann, M., 2005. Photoenhanced uptake of gaseous NO2 on solid organic compounds: a photochemical source of HONO? Faraday Discuss. 130, 195e210. Gligorovski, S., Weschler, C.J., 2013. The oxidative capacity of indoor atmospheres. Environ. Sci. Technol. 47 (24), 13905e13906. mez Alvarez, E., Amedro, D., Afif, C., Gligorovski, S., Schoemacker, C., Fittschen, C., Go Doussin, J.-F., Wortham, H., 2013. Photolysis of nitrous acid as a primary source of OH radicals indoors. Proc. Natl. Acad. Sci. U. S. A. 33, 13294e13299. mez Alvarez, E., So €rgel, M., Gligorovski, S., Bassil, S., Bartolomei, V., Coulomb, B., Go Zetzsch, C., Wortham, H., 2014. Light-induced nitrous acid (HONO) production from NO2 heterogeneous reactions on household chemicals. Atmos. Environ. 95, 391e399. Monn, C., 2001. Exposure assessment of air pollutants: a review on spatial heterogeneity and indoor/outdoor/personal exposure to suspended particulate matter, nitrogen dioxide and ozone. Atmos. Environ. 35, 1e32. Nazaroff, W.W., Cass, G.R., 1989. Mathematical modeling of chemically reactive pollutants in indoor air. Environ. Sci. Technol. 23, 157e166. Pitts Jr., J.N., 1983. Formation and fate of gaseous and particulate mutagens and carcinogens in real and simulated atmospheres. Environ. Health Perspect. 47, 115e140.
Shapley, D., 1976. Nitrosamines: scientists on the trail of prime suspect in urban cancer. Science 191, 268e270. Shapiro, R., Dubelman, S., Feinberg, A.M., Crain, P.F., McCloskey, J.A., 1977. Isolation and identification of cross-linked nucleosides from nitrous acid treated deoxyribonucleic acid. J. Am. Chem. Soc. 99, 302e303. Sleiman, M., Gundel, L.A., Pankow, J.F., Jacob, P., Singer, B.C., Destaillats, H., 2010. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smokehazards. Proc. Natl. Acad. Sci. U. S. A. 107, 6576e6581. Stemmler, K., Ammann, M., Donders, C., Kleffmann, J., George, C., 2006. Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid. Nat. Chem. 440, 195e198. Stone, D., Whalley, K.L., Heard, E.D., 2012. Tropospheric OH and HO2 radicals: field measurements and model comparisons. Chem. Soc. Rev. 41 (19), 6348e6404. Weschler, C.J., Shields, H.C., 1996. Production of the hydroxyl radical in indoor air. Environ. Sci. Technol. 30, 3250e3258.
Sasho Gligorovski*, Henri Wortham Aix Marseille University, CNRS, Laboratoire de Chimie de l'Environnement (FRE 3416), (Case 29), 3 Place Victor Hugo, F e 13331 Marseille Cedex 3, France € rg Kleffmann Jo €t Wuppertal, Gaußstr. Physikalische Chemie/FB C, Bergische Universita 20, 42119 Wuppertal, Germany E-mail address: [email protected]. * Corresponding author. E-mail address: [email protected] (S. Gligorovski).
25 July 2014 Available online 16 October 2014