深圳大气PM2.5中水溶性有机物的来源特征

Source apportionment of water-soluble organic matter in PM2.5 in Shenzhen

对2017年9月~2018年8月深圳市北部大气PM2.5中水溶性有机物(WSOM)的质量浓度、质谱及来源结构进行测量和分析.结果表明:PM2.5的质量浓度为(32.3±18.4)μg/m^3,WSOM的质量浓度为(9.4±5.7)μg/m^3,占颗粒物总有机物的(77.6%±14.0%).质谱分析显示,WSOM的氧碳比(O/C)平均值达到(0.57±0.09),属于二次有机物的O/C值范围,且生物质燃烧排放的离子碎片C2H4O^2+的丰度显著,说明WSOM的来源中有显著的生物质燃烧排放的有机气溶胶.为了明确WSOM的来源结构,利用正矩阵因子分解法(PMF)模型进行来源解析,发现3个合理因子:高氧化态有机气溶胶(MO-OOA),低氧化态有机气溶胶(LO-OOA)和生物质燃烧(BBOA),贡献比例分别为51.7%,31.8%和16.5%.MO-OOA和BBOA贡献浓度均呈现秋冬高、春夏低的季节变化特征,反向轨迹分析显示其与内陆污染传输关系密切.LO-OOA的变化相对稳定,本地源的贡献较大.结合14C同位素示踪法对秋冬季WSOM样品分析,发现机动车等化石源二次有机物是WSOM的主要来源,贡献比例达到53.9%,需继续加强对化石燃料控制来降低WSOM污染.

This study systematically analyzed the Water-Soluble Organic matter(WSOM)in PM2.5 collected during September 2017 to August 2018 in the northernzone in Shenzhen.The mass concentration,mass spectraand sources of WSOM were obtained.The average mass concentration of PM2.5 was(32.3±18.4)μg/m^3.WSOM was determined to be 77.6%±14.0%of the organic matter(OM),with anaverage mass concentration of(9.4±5.7)μg/m^3.As shown in the mass spectrometry,the average O/C ratio of WSOM was 0.57±0.99,which was within thetypical range ofthe O/C valuesof SOA.Meanwhile,the abundant C2H4O^2+proved that biomass burning organic aerosol(BBOA)contributed significantly to the WSOM.Furthermore,positive matrix factorization(PMF)model was applied to perform source apportionment of WSOM and three reasonable factors were identified,including BBOA,more oxidized oxygenated OA(MO-OOA)and less oxidized oxygenated OA(LO-OOA),accounting for 16.5%,51.7%and 31.8%,respectively.Compared to spring and summer,BBOA and MO-OOAcontributed more in autumn and winter,which was more closely related to inland pollution transport based on backward trajectory analysis.Thelittle variation of LO-OOA in different air masses possibly impliedits local sources.14C measurement was conducted to help separate fossil and non-fossil emissions of WSOM,and the fossil fuel-derived secondary organic matterwas found to dominate the WSOM mass(53.9%).Therefore,it’s necessary to strengthen the control of fossil fuel sources in order to reduce WSOM pollution.