Biomass burning dominates brown carbon absorption in the rural southeastern United States Geophysical Research Letters

Brown carbon aerosol consists of light-absorbing organic particulate matter with wavelength-dependent absorption. Aerosol optical extinction, absorption, size distributions, and chemical composition were measured in rural Alabama during summer 2013. The field site was well located to examine sources of brown carbon aerosol, with influence by high biogenic organic aerosol concentrations, pollution from two nearby cities, and biomass burning aerosol. We report the optical closure between measured dry aerosol extinction at 365nm and calculated extinction from composition and size distribution, showing agreement within experiment uncertainties. We find that aerosol optical extinction is dominated by scattering, with single-scattering albedo values of 0.940.02. Black carbon aerosol accounts for 919% of the total carbonaceous aerosol absorption at 365nm, while organic aerosol accounts for 99%. The majority of brown carbon aerosol mass is associated with biomass burning, with smaller contributions from biogenically derived secondary organic aerosol. 2015 Grant no. NA13OAR4310063 OAR (Oceanic and Atmospheric Research) ESRL (Earth System Research Laboratory) Submitted http://dx.doi.org/10.1002/2014gl062444 Other 1878