Size distributions of low molecular weight dicarboxylic acids, ketocarboxylic acids, glyoxal and methylglyoxal in the marine aerosols from Okinawa Island, Japan

Size-segregated marine aerosol samples (5 sets) were collected in 2008 spring at Cape Hedo Station of National Institute of Environmental Studies, Okinawa (128.25° E, 26.87° N), an outflow region of Chinese aerosols and their precursors, using an Andersen middle volume impactor at a flow rate of 100 lpm and pre-combusted quartz fiber filters. The samples were analyzed for low molecular weight diacids and related compounds, using a capillary gas chromatography and GC/MS after BF3/n-butanol derivatization. Particle size cuts (8 stages + BUF) are 0.43, 0.65, 1.1, 2.1, 3.3, 4.7, 7 and 11.3 µm in diameter. Homologous series of aliphatic (C2-C12) and aromatic (phthalic, iso- and tere-phthalic) diacids were detected as well as w-oxoacids (C2-C9), glyoxal and methylglyoxal. Oxalic acid (C2) was found as the dominant diacid in all the size ranges, followed by malonic (C3) and succinic (C4) acids. Glyoxylic (wC2) acid was the most abundant ketoacid followed by wC4 acid. Most of the organic species maximized in fine mode of 0.65-1.1 or 1.1-2.1µm. Oxalic acid (C2, 4.4-70.6 ngm-3, av. 23.9 ngm-3) comprised 54-80% (av. 67%) of total diacid concentrations. The small diacids showed concentration peaks on fine mode, suggesting that they are produced by photochemical oxidation of volatile organic precursors during long-range atmospheric transport from Asian Continent. They may also be produced by heterogeneous reactions in the atmospheric particles (dusts and cloud droplets).