Stable carbon isotopic composition of low-molecular-weight dicarboxylic acids and ketoacids in remote marine aerosols

[ 1] We determined stable carbon isotopic composition (delta C-13) of C-2 to C-9 dicarboxylic acids (DCAs) and some ketoacids in the marine aerosols from the western Pacific and Southern Ocean (35 degrees N to 65 degrees S). On average, oxalic ( mean, - 16.8 parts per thousand), adipic ( - 17.2 parts per thousand), and glyoxylic ( - 17.6 parts per thousand) acids showed heavier delta C-13, whereas maleic ( - 24.2 parts per thousand), methylmalonic ( - 23.6 parts per thousand), and phthalic ( - 23.1 parts per thousand) acids were more depleted in C-13. Oxalic acid presented very diverse delta C-13 values ( - 27 to -7 parts per thousand), which increased from midlatitudes toward the equator. A similar latitudinal trend of delta C-13 was also found for malonic, succinic, and adipic acids. However, such a trend was not observed for phthalic, maleic, and glyoxylic acids. We suggest that the delta C-13 increase toward the equator is associated with photochemically aged air masses, in which kinetic isotope effects for photochemical degradation of DCAs may be important. Differences in delta C-13 of some saturated DCAs were also found to increase from midlatitudes to the equator.