Water-soluble dicarboxylic acids in the tropospheric aerosols collected over east Asia and western North Pacific by ACE-Asia C-130 aircraft : Characterization of Asian aerosols and their radiative impacts on climate

Tropospheric aerosols were collected during C-130 aircraft campaign over the east Asia/Pacific region in April to May 2001 and were analyzed for low molecular weight dicarboxylic acids. Homologous series of C 2 -C 5 dicarboxylic acids were detected, for the first time, in the polluted troposphere in the Asian region using aircraft. Oxalic acid (C 2 ) was found to be the most abundant species followed by malonic (C 3 ) or succinic (C 4 ) acid. Total concentrations of C 2 -C 5 diacids (44-870 ng m-3, average 310 ng m -3 ) are similar to those reported in urban Tokyo near the ground level. Concentrations of oxalic acid showed a positive correlation (r2 = 0.70) with total organic carbon (TOC), although other diacids showed weaker positive correlation. These results suggest that water-soluble dicarboxylic acids and TOC were emitted from similar sources on the ground in the Asian continent and/or produced by the photochemical oxidation of anthropogenic organic compounds in the atmosphere. The diacid-carbons were found to comprise 0.2-3.3% (average 1.8%) of TOC. Water-soluble dicarboxylic acids may play an important role in controlling the chemical and physical properties of organic aerosols in the polluted troposphere over the east Asia and the western Pacific.