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Abstract.A spectroscopic analysis of 115 wintertime particulate matter samples collected in rural California shows that wood smoke absorbs solar radiation with a strong spectral selectivity. This is consistent with prior work that has demonstrated that organic carbon (OC), in addition to black carbon (BC), appreciably absorbs solar radiation in the visible and ultraviolet spectral regions. We apportion light absorption to OC and BC and find that the absorptionÅngström exponent of the light-absorbing OC in these samples ranges from 3.0 to 7.4 and averages 5.0. Further, we calculate that OC would account for 14 % and BC would account for 86 % of solar radiation absorbed by the wood smoke in the atmosphere (integrated over the solar spectrum from 300 to 2500 nm). OC would contribute 49 % of the wood smoke particulate matter absorption of ultraviolet solar radiation at wavelengths below 400 nm and, therefore, may affect tropospheric photochemistry. These results illustrate that BC is the dominant light-absorbing particulate matter species in atmospheres burdened with residential wood smoke and OC absorption is secondary but not insignificant. Further, these results add to the growing body of evidence that lightabsorbing OC is ubiquitous in atmospheres influenced by biomass burning and may be important to include when considering particulate matter effects on climate.

Continuous, size resolved particle measurements were performed in two houses in order to determine size-dependent particle penetration into and deposition in the indoor environment. The experiments consisted of three parts: (1) measurement of the particle loss rate following artificial elevation of indoor particle concentrations, (2) rapid reduction in particle concentration through induced ventilation by pressurization of the houses with HEPA-filtered air, and (3) measurement of the particle concentration rebound after house pressurization stopped. During the particle concentration decay period, when indoor concentrations are very high, losses due to deposition are large compared to gains due to particle infiltration. During the concentration rebound period, the opposite is true. The large variation in indoor concentration allows the effects of penetration and deposition losses to be separated by the transient, two-parameter model we employed to analyze the data. For the two houses studied, we found that as particles increased in diameter from 0.1 to 10 µm, penetration factors ranged from ∼1 to 0.3 and deposition loss rates ranged from 0.1 and 5 h −1 . The decline in penetration factor with increasing particle size was less pronounced in the house with the larger normalized leakage area.

Recent studies associate particulate air pollution with adverse health effects; however, the exposure to indoor particles of outdoor origin is not well characterized, particularly for individual chemical species. We conducted a field study in an unoccupied, single-story residence in Clovis, California to provide data and analyses to address issues important for assessing exposure. We used real-time particle monitors both outdoors and indoors to quantify PM-2.5 nitrate, sulfate, and carbon. The results show that measured indoor ammonium nitrate concentrations were significantly lower than would be expected based solely on penetration and deposition losses. The additional reduction can be attributed to the transformation indoors of ammonium nitrate into ammonia and nitric acid gases, which are subsequently lost by deposition and sorption to indoor surfaces. A mass balance model that accounts for the kinetics of ammonium nitrate evaporation was able to reproduce measured indoor ammonium nitrate and nitric acid concentrations, resulting in a fitted value of the deposition velocity for nitric acid of 0.56 cm s -1 . The results indicate that indoor exposure to outdoor ammonium nitrate in Central Valley of California are small, and suggest that exposure assessments based on total particle mass measured outdoors may obscure the actual causal relationships for indoor exposure to particles of outdoor origin.

To facilitate routine health risk assessments, we develop

Spectroscopic analysis shows that 115 residential wood smoke-dominated particulate matter samples absorb light with strong spectral selectivity, consistent with prior work that has demonstrated that organic carbon (OC), in addition to black carbon (BC), appreciably absorbs solar radiation in the visible and ultraviolet spectral regions. Apportionment of light absorption yields the absorption Ångström exponent of the light absorbing OC in these samples, which ranges from 3.0 to 7.4 and averages 5.0, and indicates that OC and BC, respectively, would account for 14% and 86% of solar radiation absorbed by the wood smoke in the atmosphere (integrated over the solar spectrum from 300 to 2500 nm). OC would contribute 49% of the wood smoke particulate matter absorption of ultraviolet solar radiation at wavelengths below 400 nm. These results illustrate that BC is the dominant light absorbing particulate matter species in atmospheres burdened with residential wood smoke and OC absorption is secondary but not insignificant. Further, since biomass combustion generates a major portion of atmospheric particulate matter globally, these results suggest that OC absorption should be included when particulate matter effects on the radiative forcing of climate are considered, and that OC absorption may affect the ultraviolet actinic flux and thus tropospheric photochemistry

Recent studies associate particulate air pollution with adverse health effects. The indoor exposure to particles of outdoor origin is not well characterized, particularly for individual chemical species. In response to this, a field study in an unoccupied, singlestory residence in Clovis, California was conducted. Real-time particle monitors were used both outdoors and indoors to quantity PM2.5 nitrate, sulfate, and carbon. The aggregate of the highly time-resolved sulfate data, as well as averages of these data, was fit using a time-averaged form of the infiltration equation, resulting in reasonable values for the penetration coefficient and deposition velocity. In contrast, individual values of the indoor/outdoor ratio can vary significantly from that predicted by the model for time scales ranging from a few minutes to several hours. Measured indoor ammonium nitrate levels were typically significantly lower than expected based solely on penetration and deposition losses. The additional reduction is due to the transformation of ammonium nitrate into ammonia and nitric acid gases indoors, which are subsequently lost by deposition and sorption to indoor surfaces. This result illustrates that exposure assessments based on total outdoor particle mass can obscure the actual causal relationships for indoor exposures to particles of outdoor origin.