Abstract
Size-segregated aerosol samples were collected in Singapore and Indonesia during forest fire event and afterward in 1997. They were analyzed for dicarboxylic acids, ketoacids and dicarbonyls using a capillary GC and GC/MS. Molecular composition of the dicarboxylic acids and the related compounds showed that oxalic (C2) acid was the most abundant species followed by malonic (C3) and succinic (C4) acids. Concentrations of dicarboxylic acids in fine aerosol particles (diameter<2.1μm) collected in Singapore during intensive forest fires were formed to be more than 3 times higher than those collected afterward. This suggests that the dicarboxylic acids associated with forest fire are more concentrated in fine particles. During the forest fire, volatile organic compounds are likely generated by the combustion process of trees and are oxidized to dicarboxylic acids by photochemical reactions. The diacids are probably condensed in fine particle size. However, it is not easy to distinguish between the diacids directly produced by biomass burning and secondary produced by photooxidation. Dicarboxylic acids such as C3, C4 and azelaic (C9) acid that were most abundant in the coarse particles (diameter2.1-11μm) are suggested to be formed by atmospheric heterogeneous reaction on aerosol surfaces.
