常州市大气PM_(2.5)中PAHs污染特征及来源解析

Pollution Characteristics and Source Identification of PAHs in Atmospheric PM_(2.5) in Changzhou City

2016年1~8月期间,在常州市采集到55个大气细颗粒物PM_(2.5)样品,采用气相色谱-质谱联用仪测定其中17种PAHs的含量.结果表明,冬、春、夏季PAHs的季均浓度分别为140.24、41.42和2.96 ng·m^(-3),冬季污染较严重,且以4~6环中高分子量化合物为主.Ba P日均浓度平均值3.64 ng·m^(-3),超标日占总采样天数的41%.PAHs浓度与气温(相关系数-0.643)和能见度(相关系数-0.466)显著负相关,与大气压呈显著正相关(相关系数0.544),而与风速、相对湿度相关性较差.受昼夜温差、大气层结和污染源变化等因素影响,夜间PAHs浓度高于白天.气团后向轨迹模型分析表明,常州PM_(2.5)中PAHs主要受当地排放源和短距离传输的影响,长距离传输影响小(仅占11%).特征比值法分析发现,PAHs主要来源于燃煤、机动车尾气和生物质燃烧.利用超额终生致癌风险(ILCR)模型评估PAHs通过呼吸暴露途径对人体健康的影响,结果表明:成人的ILCR值高于儿童,冬季和春季人群的ILCR值略高于风险阈值,夏季则不明显.

A total of 55 ambient fine particle（ PM_（2. 5）） samples were collected in Changzhou City from January to August 2016. The concentrations of 17 PM_（2. 5）-bound PAHs in the samples were analyzed by GC-MS. Results showed that seasonal average mass concentrations of PAHs in winter,spring,and summer were 140. 24,41. 42,and 2. 96 ng·m^（-3）,respectively,which indicating that the pollution of PAHs in winter appeared more serious than in the other two seasons,and 4-6-ring high molecular weight PAHs were predominant in all three seasons. The average daily level of Ba P was 3. 64 ng·m^（-3）and the days it exceeded the permitted standard accounted for 41% of total days. PAH concentration had significant negative correlations with temperature（ correlation coefficient：-0. 643） and visibility（ correlation coefficient：-0. 466）,whereas it had good positive correlations with atmospheric pressure（ correlation coefficient： 0. 544） and poor correlations with wind speed and relative humidity. PAH concentrations were higher at nighttime than at daytime,because of the influences of temperature difference,atmospheric stratification,as well as pollution sources.The results from the air backward trajectory model indicated that PM_（2. 5）-bound PAHs in Changzhou were mainly affected by local emission sources and short-distance transportation,whereas the contribution of long-distance transmission was small（ only 11%）.Based on analysis of characteristic ratios,PAHs were mainly sourced from coal burning,vehicle emissions,and biomass burning. An incremental lifetime cancer risk（ ILCR） model was used to evaluate the health impact of PAHs via breathing exposure pathways.Results revealed that the ILCR of adults was higher than that of children. The ILCRs of the group for winter and spring were slightly higher than the risk threshold,but a difference was not obvious for summer.