Emission Factors and Optical Properties of Black and Brown Carbon Emitted at a Mixed-Conifer Forest Prescribed Burn 

Abstract. Prescribed burning is a fuel management practice employed globally that emits carbonaceous aerosols that affect human health and perturb the global climate system. Aerosol black and brown carbon (BC and BrC) emission factors were calculated from ground and aloft smoke during prescribed burns at a mixed-conifer, montane forest site in the Sierra Nevada in California. BC emission factors were 0.52 ± 0.42 and 1.0 ± 0.48 g kg-1 for the smoldering and flaming combustion phases. MCE is a poor predictor of BC emission factor, in this study and published literature. We discuss limitations of using BC to PM2.5 mass emission ratios to generate emissions inventories. Using BC emission factors measured in this study, we recommend BC to PM2.5 ratios of 0.7 % and 9.5 % for the smoldering and flaming combustion. We calculated absorption Ångström exponents (AAE) based on multiwavelength absorption for BrC and BC of 6.26 and 0.67. Using the Delta-C method with a BrC-specific absorption cross-section, we estimate a smoldering combustion BrC emission factor of 7.0 ± 2.7 g kg-1, nearly 14 and 7 times greater than the smoldering and flaming BC emission factors. Furthermore, we estimate that BrC would account for 23 % and 82 %, respectively, of the solar radiation absorbed by the smoldering smoke in the atmosphere integrated over the solar spectrum (300–2500 nm) and in the UV spectrum (300–400 nm), indicating that BrC affects tropospheric photochemistry in addition to atmospheric warming.