Biomass Burning Aerosol Emission Factor Correlation with Aerosol Angstrom Exponent

Biomass burning has a significant impact on the overall inventory of aerosols that scatter and absorb atmospheric radiation. Past research has focused on characterizing biomass burning aerosols using characteristics associated with Black Carbon (BC) and other light absorbing Organic Carbon (i.e., brown carbon, etc.) such as Modified Combustion Efficiency (MCE), BC mass concentration, and Absorption Ångström Exponent (AAE). This study develops a predictive relation between the ratio of light absorption to CO and AAE for biomass burning aerosols. Data was collected from laboratory biomass burning as well as of ambient biomass burning smoke using SP2 (BC), Picarro (CO), and PASS-3 (absorption at 405, 532, 780nm) instruments. Linear fits were used to calculate light absorption emission ratios (β (light absorption)/ΔCO and BC/ΔCO). Light absorption by BC was inferred from its mass and subtracted to isolate the absorption by other organic aerosols and curve fitting techniques were used to correlate emission ratios to AAE. Measured light absorption and BC emission ratios are reported for several fuel types and ignition methods. The resulting correlations show an inverse logarithmic relationship between emission ratios and AAE that is largely independent of fuel type and ignition method. This analysis shows that as AAE increases, the emission ratio of total absorption decreases in all wavelengths. It also shows that the contribution of organic aerosol absorption to the total absorption emission ratio is significant at all AAE values, but dominates at higher AAE values. These correlations will allow for the prediction of light absorption by BC and organic aerosol emissions from biomass burning by using CO emissions. The results of this study allow for an empirical and potentially more accurate prediction of the climate forcing potential of biomass burning emissions.