Molecular composition and size distribution of sugars, sugar-alcohols and carboxylic acids in airborne particles during a severe urban haze event caused by wheat straw burning

Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m(-3)) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2-20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (&gt;2.1 mu m) with respect to the haze and non-haze samples, but a large difference in the fine fraction (&lt;2.1 mu m) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes.</p

Selected water-soluble organic compounds found in size-resolved aerosols collected from urban, mountain and marine atmospheres over East Asia

Primary (i.e. sugars and sugar-alcohols) and secondary (i.e. carboxylic acids) water-soluble organic compounds (WSOCs) in size-segregated aerosols from the urban and mountain atmosphere of China and from the marine atmosphere in the outflow region of East Asia were characterized on a molecular level. Levoglucosan is the most abundant compound among the quantified WSOCs in the urban and mountain atmosphere, whose concentration at the urban site was 1-2 orders of magnitude higher than that at the mountain and marine sites. In contrast, malic, succinic and phthalic acids were dominant among the measured WSOCs at the marine site. In the urban air, sugars except levoglucosan gave a bimodal size distribution with a large peak in fine range (&lt;2.1 mu m) and a small peak in coarse range (&gt;= 2.1 mu m) during winter, being opposite to those in spring. In contrast, these WSOCs at the mountain and marine sites dominated in the coarse range but diminished and even disappeared in the fine range. Geometric mean diameters (GMDs) of the measured WSOCs in the fine mode at the urban site were larger in winter than in spring. Levoglucosan and carboxylic acids except for azelaic and benzoic acids showed a larger GMD in the coarse mode at the marine site probably due to an increased hygroscopic growth.</p

Comparison of dicarboxylic acids and related compounds in aerosol samples collected in Xi'an, China during haze and clean periods

PM10 aerosols from Xi&#39;an, a mega city of China in winter and summer, 2009 were measured for secondary organic aerosols (SOA) (i.e., dicarboxylic acids (DCA), keto-carboxylic acids, and &alpha;-dicarbonyls), water-soluble organic (WSOC) and inorganic carbon (WSIC), elemental carbon (EC) and organic carbon (OC). Molecular compositions of SOA on haze and clean days in both seasons were compared to investigate their sources and formation mechanisms. DCA in the samples were 1843&plusmn;810ngm-3 in winter and 1259&plusmn;781ngm-3 in summer, respectively, which is similar and even higher than those measured in 2003. Oxalic acid (C2, 1162&plusmn;570ngm-3 in winter and 1907&plusmn;707ngm-3 in summer) is the predominant species of DCA, followed by t-phthalic (tPh) in winter and phthalic (Ph) in summer. Such a molecular composition is different from those in other Asian cities where succinic acid (C4) or malonic acid (C3) is the second highest species, which is mostly due to significant emissions from household combustion of coal and open burning of waste material in Xi&#39;an. Mass ratios of C2/diacids, diacids/WSOC, WSOC/OC and individual diacid-C/WSOC are higher on the haze days than on the clean days in both seasons, suggesting an enhanced SOA production under the haze condition. We also found that the haze samples are acidic while the clean samples are almost neutral. Such a difference in particle acidity is consistent with the enhanced SOA production, because acid-catalysis is an important aqueous-phase formation pathway of SOA. Gly/mGly mass ratio showed higher values on haze days than on clean day in both seasons. We comprehensively investigated the ratio in literature and found a consistent pattern. Based on our observation results and those documented data we proposed for the first time that concentration ratio of Gly/mGly can be taken as an indicator of aerosol ageing.</p

Comparison of abundances, compositions and sources of elements, inorganic ions and organic compounds in atmospheric aerosols from Xi'an and New Delhi, two megacities in China and India

Wintertime TSP samples collected in the two megacities of Xi&#39;an, China and New Delhi, India were analyzed for elements, inorganic ions, carbonaceous species and organic compounds to investigate the differences in chemical compositions and sources of organic aerosols. The current work is the first time comparing the composition of urban organic aerosols from China and India and discussing their sources in a single study. Our results showed that the concentrations of Ca, Fe, Ti, inorganic ions, EC, PAHs and hopanes in Xi&#39;an are 1.3-2.9 times of those in New Delhi, which is ascribed to the higher emissions of dust and coal burning in Xi&#39;an. In contrast, Cl- levoglucosan, n-alkanes, fatty alcohols, fatty acids, phthalates and bisphenol A are 0.4-3.0 times higher in New Delhi than in Xi&#39;an, which is attributed to strong emissions from biomass burning and solid waste incineration. PAHs are carcinogenic while phthalates and bisphenol A are endocrine disrupting. Thus, the significant difference in chemical compositions of the above TSP samples may suggest that residents in Xi&#39;an and New Delhi are exposed to environmental hazards that pose different health risks. Lower mass ratios of octadecenoic acid/octadecanoic acid (C-18:1/C-18:0) and benzo(a)pyrene/benzo(e)pyrene (BaP/BeP) demonstrate that aerosol particles in New Delhi are photochemically more aged. Mass closure reconstructions of the wintertime TSP indicate that crustal material is the most abundant component of ambient particles in Xi&#39;an and New Delhi, accounting for 52% and 48% of the particle masses, respectively, followed by organic matter (24% and 23% in Xi&#39;an and New Delhi, respectively) and secondary inorganic ions (sulfate, nitrate plus ammonium, 16% and 12% in Xi&#39;an and New Delhi, respectively).</p