南京冬季市区和郊区气溶胶中PAHs浓度的昼夜特征及粒径分布

Size Distributions and Diurnal Variations in the Concentrations of Polycyclic Aromatic Hydrocarbons in Winter in Urban and Suburban Nanjing,China

为了研究南京市区与郊区气溶胶中多环芳烃(PAHs)污染状况和分布特征,利用气-质联用仪(GC-MS)分析了2010年1月1～10日日间和夜间分别在南京大学和南京信息工程大学采集的气溶胶样品,得到南京市区与郊区17种PAHs浓度,总浓度分别为41.36～220.35 ng.m-3和45.10～200.86 ng.m-3,其中约66%～67%分布于细粒子(Dp≤2.1μm)中.研究发现,南京市区和郊区气溶胶中PAH总浓度均处于较高的水平;但两者昼夜变化趋势不同,即市区PAH总浓度日间高于夜间,郊区PAH总浓度日间低于夜间.主导风向的改变和高压天气系统对PAH浓度变化影响较大;在市区其影响主要表现在细粒子部分,而郊区主要表现在粗粒子部分.市区和郊区不同环数的PAHs粒径分布不同;2～3环PAHs,郊区含量高于市区;而4～6环PAHs,市区含量高于郊区.高环数(4～6环)PAHs在粗模态出现较大浓度峰可能是由于南京地区粗模态气溶胶中碳含量较高.市区和郊区相似的特征比值说明两者的PAHs具有相同污染来源,主要为生物质及煤的燃烧和汽车尾气,表明南京市区PAHs受到郊区工业源排放影响较大.

The contamination status and distribution characteristics of particulate polycyelic aromatic hydrocarbons （PAHs） were investigated in aerosols of urban and suburban Nanjing. A total of 17 PAHs were analyzed in the aerosol samples collected in daytime and nighttime during January 1th to 10th , 2010 in Nanjing University （NU） and Nanjing University of Information Science ＆ Technology （NUIST）. The PAH concentrations at the urban and suburban sites were 41.36-220. 35 ng.m 3 and 45. 10-200.86 ng＇m 3 respectively, of which about 66%-67% was absorbed by fine particles （Dp〈2.1 p,m）. High levels of particulate PAHs were detected at both sampling sites with different diurnal variations. The higher total-PAH concentration occurred in the daytime at the urban site and in the nighttime at the suburban site. The change of prevailing wind direction and high-pressure weather system had significant impact on the variation of PAH concentrations, which were dominated by fine and coarse particles in urban and suburban regions, respectively. Difference in PAH size distributions was found for low weight molecular PAHs （LWM-PAH） and high weight molecular PAHs （HWM-PAH） in urban and suburban areas. The concentrations of 2-3 ring PAHs were higher at the suburban site than those at the urban site, whereas larger amounts of 4-6 ring PAHs were found at the urban site than at the suburban site. The concentration peaks in coarse particle size of high-molecular-weight PAHs found in our study were larger than those in some of the previous studies, which might be due to the high carbon content in coarse particles in the atmosphere at our sites. Analysis of diagnostic ratios indicated that the PAHs particles at both two sites have the same sources, including combustion of coal and biomass, vehicular exhaust and suburban industrial emission.