Study On Sources And Formation Of Atmospheric Particulate Dicarboxylic Acids In Qianliyan Island

Study on chemical composition characteristic of particulate dicarboxylic acids,which could influence human health, radiation balance, climate, and formationmechanisms of secondary organic aerosol (SOA), have received more attention inrecent years. We can estimate the formation mechanisms of dicarboxylic acid thoughits size distribution as different distribution modes of chemical constituents inatmospheric particle may reflect various sources. There is no much systematicunderstanding on the sources and formation mechanisms of particulate dicarboxylicacids in Qianliyan Island so far. Based on the size distribution measurement samplescollected during the period from24th April to4th May,2011in Qianliyan Islandfollowed by analyzed using IC (Ion Chromatography), the sources and formationmechanisms of dicarboxylic acids, i.e. oxalate, malonate, and succinate, are discussed.The different characteristics of size distributions of major chemical constituents indifferent weathers (i.e. sunny and dust weather) are compared and diurnal variation isalso analyzed. The main conclusions are shown as follows:(1)The size distributions of major ionic species are complex since the influence oflocal pollution source, i.e. generating equipment, in Qianliyan Island can not beignored. Moreover, the concentrations of ionic species are relatively high in the rangeof <0.048μm and>9.9μm in sometimes. However, this kind of influence is muchmore significant in sunny days.(2)There are mainly two concentration distribution modes (i.e. droplet mode andcoarse mode) of particulate oxalate in both weather conditions. The peak range ofeach mode is0.54~1.0μm and3.1~6.2μm respectively, while the former one is thedominant mode all the time. Although the numbers of samples in sunny days are more than twice of that in dust weather, the concentration of oxalate is obviously higher andthe bimodal distribution of oxalate is much more significant in dust weather. Andmeanwhile there is no significant increase of concentration in coarse particle rangeof>6.2μm. It’s different from oxalate that malonate and succinate have no obviousdroplet mode but present condensation mode (0.093~0.32μm) and coarse particlemode (1.8~6.2μm) in some times. Succinate in dust weather shows a condensationmode in range of0.093~0.32μm while its concentration is higher than that in sunnydays. In other hand, the concentration of malonate is decreased during the dustweather, however, it presents obvious condensation mode in the daytime and coarsemode in nighttime.(3)Particulate dicarboxylic acids in Qianliyan Island may come from continentsource followed by marine source in sunny days. Liquid phase reaction in cloudprocess dominates the formation of oxalate in droplet mode(0.54~1.0μm) during thedaytime while other mode distributions may resulted from gas-particle condensationformation, heterogeneous formation, and metabolic activity of fungi from marinesource. Moreover, heterogeneous reaction may be a major pathway to generateoxalate in particles with coarse size. In nighttime, the formation of particle oxalate indroplet mode is affected by the cloud process while heterogeneous reaction betweengaseous precursors and sea-salt aerosol may dominates its distribution in coarse sizemode.(4)In dust weather, the sources of particulate dicarboxylic acids in QianliyanIsland are greatly influenced by continent sources of East Asia. Meanwhile, dustaerosol from long distance transport could be an important source of dicarboxylicacids or precursors, since the concentration ratios of malonate to succinate in thedaytime and nighttime are0.23and0.29respectively which are obviously lower thanthat in sunny days. Particulate oxalate always distributes in droplet mode in range of0.54~1.8μm in the daytime during dust weather. The correlation coefficients betweenoxalate and nitrate, ammonium and magnesium are0.90,0.88and0.86respectivelywhich means that oxalate may be produced from gaseous photochemical reaction and cloud process. Additionally, particulate oxalate in dust weather presents bimodaldistribution in nighttime as well as in sunny days. The correlation coefficientsbetween oxalate and nitrate, ammonium and non-sea-salt sulfate are0.98,0.87and0.80, respectively. Therefore, the conclusion is indicated that the major formationmechanisms of oxalate in droplet mode and coarse mode are cloud process andheterogeneous reaction on the surface of dust aerosol, respectively.