Changes in the Size Distributions of Oxalic Acid and Related Polar Compounds Over Northern Japan During Spring.

Size distributions of chemical species provide evidence for their sources and formation mechanisms. Size‐segregated aerosols with 12 sizes were collected over Northern Japan (Sapporo: 43.07°N and 141.35°E) during the spring (9 April–21 May) of 2001 and analyzed for water‐soluble organic and inorganic species. The dominances of SO42– and NH4+ in submicron (Da < 1.1 μm) and Na+ and Ca2+ in supermicron (Da > 1.1 μm) aerosols suggest substantial contributions from anthropogenic sources, sea‐salt and dust particles via long‐range atmospheric transport. Oxalic acid (C2) is the dominant organic species followed by malonic (C3) and succinic (C4) acid. A supermicron mode enrichment of C2 is heavily involved with the long‐range transport of dust particles, whereas submicron mode C2 was influenced by anthropogenic sources from the East Asian continent. The size distributions of shorter‐chain diacids (C3–C6), phthalic (Ph) and glyoxylic acid are consistent with those of C2, whereas azelaic acid (C9) is enriched in submicron and supermicron modes by the influences of continental and marine air masses. The mass concentration ratios of C3/C4 in submicron (1.5–2.3) and supermicron (1.2–1.8) mode demonstrated that water‐soluble organic aerosols in Sapporo were photochemically processed during long‐range transport. The Ph/C9 ratios show that the influence of anthropogenic sources on 9–28 April samples was pronounced in supermicron (2.5–2.9) than the submicron (1.1–1.2) particles, and vice‐versa on 6–21 May samples. These contrast distributions suggest that the continental air masses from East Asia and marine air masses from the surrounding ocean likely control the chemical composition of aerosols over Northern Japan. Plain Language Summary: Dicarboxylic acids make up a considerable portion of water‐soluble organic aerosols (OAs) in the atmosphere. We present the changes in the size distributions of water‐soluble secondary OAs during the ACE‐Asia campaign in the spring of 2001 in Northern Japan. The molecular distribution of dicarboxylic acids in size‐segregated aerosols with a predominance of oxalic acid (C2) followed by malonic acid implies that water‐soluble OAs over Northern Japan were photochemically aged. The substantial fraction of C2 on the supermicron mode aerosols is affected by the dust transported from the East Asian continent, suggesting its uptake or heterogeneous production on the surface of dust particles during long‐range transport to Northern Japan. Significant positive correlations of C2 and related compounds with Ca2+ in a supermicron mode further support a heterogeneous production of C2 in Ca2+‐enriched supermicron aerosols. The results suggest that the air masses from East Asia and the surrounding ocean mainly control the abundances of OAs over Northern Japan. The atmospheric abundance of secondary OAs could change due to the enhanced production of C2 in supermicron and submicron particles that can affect aerosol‐cloud interaction and radiative forcing of the most considerable fraction of water‐soluble secondary OAs. Key Points: The chemical composition of atmospheric aerosols over Northern Japan is controlled by continental and marine air massesOxalic acid size distribution is induced by the long‐range transport of dust particles and anthropogenic sourcesWater‐soluble organic aerosols over Northern Japan were photochemically processed during long‐range atmospheric transport [ABSTRACT FROM AUTHOR]