Light absorption enhancement due to mixing in black carbon and organic carbon generated during biomass burning

Abstract We report the direct observation of the light absorption enhancement effect due to the mixing of black carbon (BC) and organic carbon (OC) aerosols generated during biomass combustion. The biomass fuels viz. mango tree wood (Mangifera indica) and dung cake were burned and the dry absorption of the aerosol stream was measured using the 7-wavelength aethalometer. The absorption coefficients were measured for thermally denuded and undenuded aerosols. The measurements provided an enhancement ratio for black carbon in presence of organic carbon at seven different wavelengths. The near-source enhancement ratio for wood and dung cake at 880 nm was found to be 1.35 ± 0.06 and 1.59 ± 0.08, respectively. The enhancement effect was found to increase with the decrease in wavelength for both the fuels, indicating absorption by the brown carbon. The organic coating on the black carbon was estimated using the mie theory modelling. The organic coating factor on the black carbon was found to be 1.37 and 1.69 for wood and dung cake, respectively. The enhancement ratio at 370 nm increased with the increase in the absorption angstrom exponent (AAE). The enhancement ratio depicted negative linear dependence (r = −0.91) on the logarithmic ratio of black carbon and absorption coefficients of brown carbon at 370 nm across both fuels and burn conditions.