Distribution and stable carbon isotopic composition of dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls in fresh and aged biomass burning aerosols

Abstract. Biomass burning (BB) is a significant source for dicarboxylic acids (diacids) and related compounds that play important roles in atmospheric chemistry and climate change. In this study, a combustion chamber and oxidation flow reactor were used to generate fresh and aged aerosols from burned rice, maize, and wheat straw to investigate atmospheric aging and the stable carbon isotopic (δ13C) composition of these emissions. Succinic acid (C4) was the most abundant species in fresh samples; while, oxalic acid (C2) became dominant after atmospheric aging. Of all diacids, C2 had the highest aged to fresh emission ratios of 50.8 to 64.5, suggesting that C2 is largely produced through secondary photochemical processes. Compared with fresh samples, the emission factors of ketocarboxylic acids and α-dicarbonyls increased after 2-day but decreased after 7-day aging, indicating short residence time and further atmospheric degradation from 2- to 7-days. The C2 δ13C values for aged biomass samples were higher than those of urban aerosols but lower than marine or mountain aerosols, and the C2 δ13C became isotopically heavier during aging. Relationships between the reduction in volatile organic compounds (VOCs), such as toluene, benzene, and isoprene, and increase in dicarboxylic acids after 2-day aging indicate that these volatile organic compounds led to the formation of dicarboxylic acids.