T. W. Kirchstetter1,2 and T. L. Thatcher3
http://www.atmos-chem-phys-discuss.net/ ... -2012.html
1Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, USA
2Civil and Environmental Engineering Department, University of California, Berkeley, USA
3Civil and Environmental Engineering Department, Cal Poly, San Luis Obispo, USA
Abstract. 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.