[1] Aerosol sampling for major oxygenated organic compounds (dicarboxylic acids, fatty acids, and levoglucosan) was conducted from 15 March to 19 April 2001 on board the National Oceanic and Atmospheric Administration R/V Ronald H. Brown over the western North Pacific, the East China Sea, and the Sea of Japan, as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign. During the cruise, aerosol particles were collected on quartz fiber filters using a high-volume air sampler. Diacids were also collected using an annular denuder sampling system to assess their gas-particle partitioning. Concentrations of total diacids, total fatty acids, and levoglucosan were found to be higher off the coasts of East Asia than in the remote Pacific. Contributions of these organic compounds to total organic carbon and total organic matter (OM) were calculated to be 9.8 ± 2.3% and 19.0 ± 4.8%, respectively, assuming OM to be organic carbon  1.6. Diacid concentrations were highly correlated with nss-SO 4 2À and NO 3 À , which originate from anthropogenic sources over East Asia. The temporal variations and chain-length distributions of fatty acids suggest that atmospheric transport of terrestrial organic materials is important off the coast of the continent. C 2 À C 5 diacids were present predominantly in the particulate phase. The relative abundances of C 2 À C 5 diacids stayed almost unchanged throughout the cruise, suggesting that deposition is more important than chemical decomposition as a sink of diacids and that they are relatively stable end products in the atmosphere.

Size‐segregated (11 stages) marine aerosol samples were collected off the coast of East Asia during the ACE‐Asia campaign in 2001 and were analyzed for homologous series of dicarboxylic acids (C2–C12), ω‐oxocarboxylic acids (C2–C4), and n‐fatty acids (C16–C30), as well as organic carbon (OC), elemental carbon, and major inorganic ions. Concentrations of OC and major diacids and oxoacids in continental polluted air masses showed predominantly submicron maxima. However, during dusty haze events, supermicron maxima were observed, suggesting a size shift due to the secondary accumulation of these components on dust as well as sea salt particles. Supermicron maxima were also found for palmitic acid (C16 fatty acid) and other lower‐molecular‐weight fatty acids (LFAs, C16–C19) that are emitted from a microlayer of the ocean surface. In contrast, higher‐molecular‐weight fatty acids (HFAs, C20–C30) were mainly detected in the submicron mode, presumably due to a substantial contribution of biomass burning aerosols. This study demonstrates a high‐variability in the size distributions of organic components (i.e., between submicron and supermicron modes) in the coastal regions off East Asia. Such variations in the physical properties of the marine aerosols may be important in relation to their cloud‐condensation‐nuclei and light extinction activities.

[1] Size distributions of C 2 -C 4 dicarboxylic acids in aerosols were studied in the marine boundary layer (MBL) of the central to western North Pacific as well as off the coasts of East Asia. C 2 -C 4 Diacids were mostly present in submicron particles over the coastal ocean, but they were relatively abundant in supermicron particles over the remote ocean. We found that the peak diameters for the concentration of C 2 -C 4 diacids in supermicron particles over the remote ocean were similar to that for the surfacearea distribution of sea salts, suggesting a deposition of gaseous diacids on sea-salt particles and/or their heterogeneous formation during long-range transport. The present results, together with the solubility product of calcium oxalate, suggest that oxalic acid in sea salts may partly form insoluble calcium salt, which potentially enhances the uptake of gaseous oxalic acid by the aerosol particles.

[1] Daytime and nighttime PM 2.5 samples were collected at the summit of Mount Tai (1534 m) located in North China Plain during a week in 2006 summer. Size-segregated aerosol particles were also collected using an eight-stage impactor during the same period. Samples were analyzed for various water-soluble organic compounds using GC/FID and GC/MS techniques. Among the species identified in PM 2.5 samples, dicarboxylic acids (C 2 -C 11 ) were found as the most abundant compound class, followed by ketocarboxylic acids, saccharides, polyols and polyacids, and dicarbonyls. Daytime concentrations of most compounds were found to be 2-3 times higher than in nighttime. Such a diurnal variation was first interpreted by the depressed transport of pollutants in nighttime from the lowlands to the mountaintop owing to the decreased heights of planetary boundary layer, and second by the photochemical production in daytime. The diurnal variation trends of secondary organic aerosols (SOA) such as diacids at the mountain site are the same as those on lowlands, but the diurnal patterns of primary organic aerosols (POA) on the mountaintop are in contrast to those on lowlands, where POA such as saccharides and polyols are usually higher in nighttime owing to the accumulation within inversion layer developed. The eight-stage impactor samples showed bimodal distributions of diacids and related compounds peaking at size ranges of 0.70-1.1 mm and 5.8-9.0 mm. In the present study, water-soluble organics in the fine mode are largely originated from biomass burning and/or photooxidation of gaseous precursors and the subsequent adsorption on the preexisting particles, whereas those in the coarse mode are mainly derived from suspended soil particles and pollens and in part via the hygroscopic growth of fine particles and formation of cloud/fog droplets.