无锡市大气PM2.5中黑碳的粒径分布与混合态特征

针对长江三角洲地区PM2.5中的重要组分黑碳(BC)气溶胶,2010~2011年利用单颗粒黑碳光度计(SP2),对江苏省无锡市夏冬两季BC气溶胶的质量浓度、粒径分布及单颗粒混合态进行了连续在线观测.结果表明,无锡市冬季BC质量浓度(6.1μg/m3)是夏季(2.5μg/m3)的2.4倍,内混态BC比例(NIB)冬季(64.8%)也显著高于夏季(44.6%),说明冬季BC污染与来外来污染传输有关.反向轨迹分析表明,来自华北平原的污染气团输入是冬季高浓度BC污染的首要原因. NIB的日变化趋势与BC质量浓度的完全相反.午后BC质量浓度最低时NIB最高,反映了二次光化学产物包覆在BC颗粒外层的老化过程.此外,夏冬两季BC粒径分布保持稳定,其质量浓度峰值对应粒径在225nm左右,数浓度峰值对应粒径在120nm左右.

Characteristics of black carbon aerosol in Wuxi

In this study, we targeted at black carbon (BC) in PM2.5in YRD and deployed a single particle soot photometer (SP2) in Wuxi City of Jiangsu Province to perform on-line characterization of major BC aerosol properties, e.g., concentrations, size distribution, and mixing state. The measurement was conducted during both the summer and winter campaigns of 2010~2011. The main finding was that, the BC pollution level increased by 2.4times from the summer (2.5μg/m3) to the winter (6.1μg/m3), together with a significant increase of the number fractions of internally mixed BC (NIB) from 44.6 to 64.8%. The high NIB level in the winter indicates that air mass transport of aged BC particles from North China was the primary reason to form the high BC pollution in the winter of Wuxi, which was further supported by the back trajectory analysis. The diurnal variations of the BC mass concentration and NIB during the campaigns showed opposite trends, with the lowest BC concentrations but the highest NIB in the daytime, reflecting the role of coating processes by photochemical production of secondary materials. In addition, the size distributions of BC in volume equivalent diameter (VED) were found to have stable lognormal patterns during the campaigns, with the peak diameter at ~120nm for the number distribution and at ~225nm for the mass distribution.