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

We determined stable carbon isotopic composition (δ 13 C) of C 2 to C 9 dicarboxylic acids (DCAs) and some ketoacids in the marine aerosols from the western Pacific and Southern Ocean (35°N to 65°S). On average, oxalic (mean, −16.8‰), adipic (−17.2‰), and glyoxylic (−17.6‰) acids showed heavier δ 13 C, whereas maleic (−24.2‰), methylmalonic (−23.6‰), and phthalic (−23.1‰) acids were more depleted in 13 C. Oxalic acid presented very diverse δ 13 C values (−27 to −7‰), which increased from midlatitudes toward the equator. A similar latitudinal trend of δ 13 C 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 δ 13 C 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 δ 13 C of some saturated DCAs were also found to increase from midlatitudes to the equator.