基于气溶胶光学特性的颗粒物来源分析

为初步探讨利用气溶胶光学指标判别污染物来源的适用性，选取天津市冬季一次重污染过程（2017年11月17—21日），对气溶胶的七波段吸收系数、三波段散射系数及其化学组分进行在线观测及分析，研究气溶胶光学特性的变化，并结合化学组分定性分析污染过程不同阶段的污染来源.结果表明:SSA（单散射反照率）可以从散射性组分和吸光性组分对消光贡献的变化判断污染来源.污染积累期，颗粒物中散射性组分（SO₄2-、NO₃-、NH₄+）的增幅高于吸光性组分EC（元素碳），导致污染积累期的SSA值高于污染前期和污染消散期，说明污染积累期存在较明显的二次转化过程.SAE（散射波长指数）可以从粒径角度推断污染来源.此次观测的污染积累期SAE值呈较明显的下降趋势，说明在细粒径段（2.5 μm以下）颗粒物粒径有增大的趋势，这主要与颗粒物中无机盐的吸湿增长及颗粒物之间的碰并有关.AAE（吸收波长指数）在一定程度上可以指示吸光颗粒物的类型.污染前期，BrC（棕色碳）在370、470 nm处对光吸收的贡献率分别为50.7%、33.8%；同期PM_2.5中ρ（Cl-）、ρ（K+）同步升高，卫星遥感显示，观测点周围有大量火点出现，推测主要受祭祖活动的影响.研究显示，气溶胶光学指标能够从散射性组分和吸光性组分对消光贡献变化、粒径变化、吸光颗粒物类型角度定性解析一部分污染来源，但其对于燃煤源和机动车等重要源类的指示作用还有待进一步研究. 

Source Analysis of Particulate Matter based on Aerosol Optical Properties

In order to explore the applicability of using aerosol optical index to identify pollutant source, the process of heavy pollution in winter in Tianjin City (November 17th-21st, 2017) was selected for online observation and analysis of the absorption coefficient of seven bands, the scattering coefficient of three bands and the chemical composition of the aerosol, to study the changes in the optical properties of the aerosol, and to qualitatively analyze the pollution sources in different stages of the pollution process in combination with the chemical composition in this study. The results show that SSA (single scattering albedo) can be used to distinguish between the source of pollution and the changes in the contribution of scattering species and light-absorbing species. During the pollution accumulation period the scattering components (SO₄2-, NO₃-, NH₄+) showed a higher growth rate than the absorption components EC, resulting in higher SSA in the pollution accumulation period than that in pre-pollution period and pollution dissipation period. In the pollution accumulation period, there was an obvious secondary transformation process. SAE (scattering angstrom exponent) can be used to infer the source of pollution from particle size. In this observation, SAE showed a significant downward trend during the pollution accumulation period, indicating that the particle size increased in the fine particle size range (below 2.5 μm), mainly due to the hygroscopic growth of particulate inorganic salts and coagulation growth of the particles. AAE (absorption angstrom exponent) can indicate the type of light-absorbing particles to some extent. In the pre-pollution period, the contribution of brown carbon to the light absorption coefficient at 370 and 470 nm was 50.7% and 33.8%, respectively. During the same period, the mass concentrations of Cl- and K+ in PM_2.5 increased simultaneously, and satellite remote sensing showed that a large number of fire spots appeared around the observation point, which was mainly affected by ancestor worship activities. It can be seen that the optical indexes can qualitatively analyze part of specific pollution sources from the contribution of scattering coefficient and absorption coefficient to extinction, particle size change and light absorbing particle type. But their indicative effects on important sources such as coal burning sources and motor vehicles need to be further studied.