西安冬季不同空气质量级别对应的PM_(2.5)化学组分变化特征

Characterization of chemical composition for fine particle matter collected in different air quality grades in Xi'an in winter

通过实验采样分析,研究了西安市冬季不同空气质量级别（HJ 633—2012）下PM2.5质量浓度及化学组分的变化特征和污染规律。结果表明,西安市2008—2009年冬季所有采样天均为轻度污染到严重污染状况,PM2.5质量浓度100%未达标（GB3095—2012）;PM2.5质量浓度及其化学组分基本随空气质量级别恶化而增加,除个别元素外,其他化学组分的质量浓度在严重污染时均出现突增,有机碳（4.5倍）和水溶性无机离子（2.7倍）的增加倍数较大;随大气污染程度的增加,人为源的重金属富集因子增加剧烈（1.6~2.0倍）,而主要来自自然源的元素富集因子变化无规律;重污染时期PM2.5中的多环芳烃（PAHs）、正构烷烃（nalkanes）均主要来自人为源排放贡献,其中生物质燃烧、低温燃煤排放是PAHs剧增的主要因素。

The ambient fine particle matters （PM2.5） were collected from November 2008 till March 2009 （wintertime） in an urban site of Xi＇an to compare with the chemical compositions according to the air quality grades guidelines （HJ 633-2012）. All of PM25 mass concentrations were in excess of the 75 μg/m3 level in the 24 h Ambient Air Quality Standards （GB 3095-2012）. The concentrations of PM2.5 mass and their corresponding chemical compositions were elevated to show a generally increasing trend of the AQI except for a few elements. The concentrations of organic carbon （OC） and water-soluble inorganic ions on six-grade days were approximately 4.5 and 2.7 times those of three-grade days. The enrichment factors of anthropogenic elements （e.g., As, Zn and Pb） on six-grade days were 1.6-2.0 times those of three-grade days, while the elements from crustal sources were not observed along with any surge and rule of air pollution levels. PAHs and n-alkanes mainly were contributed by anthropogenic sources. During the occurrence of heavy air pollution in winter, biomass burning and coal combustion emissions showed a larger contribution to PAHs than gasoline vehicle emissions.