A preliminary study on brown carbon emissions from open agricultural biomass burning and residential coal combustion in China

Recent studies suggest that, between ordinary organic carbon (OC, non-light-absorbing) and black carbon (BC, strongly light-absorbing) in atmospheric carbonaceous aerosols, there are some light-absorbing organic carbon aerosols collectively termed brown carbon (BrC). Although China has large BrC emissions from residential coal combustion and open agricultural biomass burning, there are little specific BrC emissions or testing data available. A 7-wavelength aethalometer was used to monitor the light-absorbing features of primary aerosols emissions from summertime open burning of wheat straw and from wintertime combustion of residential coal. Based on distinctions in the spectral dependence between BrC and BC (the Ångström index is theoretically 1.0 for BC and is greater than 1.0 for BrC), the relative Shares of BrC and BC (B_BrC/BC ratio) were calculated. The results show that the value was 1.754±0.278 for wheat straw and 0.183±0.142 for residential coal. Based on the BrC/BC ratios obtained, preliminary estimates of China's BrC emissions from residential coal and open agricultural biomass burning in 2000 were calculated with the help of corresponding BC emissions reported in previous studies. The yearly sum of BrC emissions from residential coal and open agricultural biomass burning was 270.6±101.6 Gg (BC equivalent) in China, with (175.4±27.8) Gg or approximately 65% attributable to field agricultural biomass and (95.2±73.7) Gg or approximately 35%, to residential coal. These findings would establish a foundation for a more comprehensive measurement of BrC emissions in the future as well as studies of BrC in atmospheric chemistry and radiation forcing.