Aircraft measurement of dicarboxylic acids in the free tropospheric aerosols over the western to central North Pacific

Aircraft observation of aerosols was conducted in February 2000, for spatial and vertical distributionsof dicarboxylic acids in the free troposphere over the western to central North Pacific. Oxalic, malonic, adipic and azelaic acids were detected in the aerosol samples as the major species. Concentrations ofthese diacids decreased exponentially with an increase in altitude. They were higher in the westernNorth Pacific (130°E) and decrease eastward. Local flights conducted over Naha (Okinawa), Iwojimaand Saipan showed that diacid concentrations decreased from the lower to upper troposphere.In the atmosphere over Saipan, where the air is not strongly affected from polluted East Asia, diacidconcentrations were almost below the detection limit. Vertical profiles of diacids over Naha and Iwojimawould be typical over the western North Pacific during winter, suggesting that diacids weresignificantly injected to the free troposphere from East Asia. Backward air mass trajectories alsosuggested that the diacids in the free troposphere over the North Pacific are strongly affected bythe outflow from East Asia. Diacids, which were produced by both primary emission and secondaryphotochemical processes in polluted air of East Asia, could alter the physico-chemical properties ofaerosols in the free troposphere over the western North Pacific.