Estimation of the Elemental to Organic Carbon Ratio in Biomass Burning Aerosol Using AERONET Retrievals

The balance between the cooling and warming effects of aerosol originating from open biomass burning (BB) critically depends on the ratio of its major absorbing and scattering components, such as elemental carbon (EC) and organic carbon (OC), but available direct measurements of this ratio in remote regions are limited and rather uncertain. Here, we propose a method to estimate the EC/OC mass ratio in BB aerosol using continuous observations of aerosol optical properties by the Aerosol Robotic Network (AERONET) and apply it to the data from two AERONET sites situated in Siberia. Our method exploits a robust experimental finding (that was reported recently based on laboratory analysis of aerosol from the combustion of wildland fuels) that the single scattering albedo of BB aerosol particles depends linearly on the EC/(EC + OC) mass ratio. We estimated that the mean value of the EC/OC ratio in BB aerosol observed in summer 2012 was 0.036 (±0.009), which is less than the corresponding value (0.061) predicted in our simulations with a chemistry transport model using the emission factors from the Global Fire Emissions Database 4 (GFED4) fire emission inventory. Based on results of our analysis, we propose a parameterization that allows constraining the EC/OC ratio in BB aerosol with available satellite observations of the absorption and extinction aerosol optical depths.