Abundances and light absorption properties of brown carbon emitted from residential coal combustion in China.

Brown carbon (BrC) fractions, including water soluble organic carbon (WSOC), water soluble humic-like substances (HULISw), alkaline soluble organic carbon (ASOC) and methanol soluble organic carbon (MSOC) were extracted from particles emitted from the residential combustion of coal with different geological maturities. The abundances and light absorption properties of these BrC fractions were comprehensively studied. The results showed that the abundances of the different constituents of the BrC fraction varied greatly with the extraction solvent, accounting for 4.3%-46%, 2.3%-23%, 3.2%-14%, and 76%-98% of the total carbon content in particles. The specific UV-Vis absorbance (SUVA254) of BrC fractions followed the order of MSOC > ASOC > HULISw > WSOC. The WSOC and MSOC fractions from the combustion of low maturity coal had relatively low SUVA254 and high SR values. The mass absorption efficiencies (MAE365) for ASOC and MSOC were higher than for WSOC, and WSOC and MSOC from low maturity coal combustion had relatively low levels of light absorption. These findings indicated that coal combustion is a potential source of atmospheric BrC and the abundance and light absorption of the coal combustion-derived BrC fractions were strongly dependent on the extraction methods used and the coal maturity rather than the coal shapes.