成都市郊冬季一次大气重污染过程化学组分粒径分布特征

The particle size distribution of chemical components during a heavy air pollution period in suburban Chengdu in winter

利用惯性撞击式8级采样器(Andersen)于2017年12月15日至2018年1月3日对成都大气颗粒物进行连续采样,结合气象观测资料和气溶胶激光雷达数据分析污染过程水溶性无机离子和碳质气溶胶粒径分布变化特征及气溶胶垂直分布演变.结果表明,二次气溶胶的形成和积累是此次污染过程发生发展的重要原因.NO_(3)^(-)和SO_(4)^(2-)重污染阶段呈单峰型分布,峰值粒径出现在0.65-1.1μm粒径段,表明主要由前提物的云内反应生成,沙尘阶段呈双峰型分布,主峰位于3.3-4.7μm,NO_(3)^(-)主要以非均相反应存在于粗粒径段中,SO_(4)^(2-)既有来自一次污染源(沙尘、土壤源等),也有来自二次氧化反应;高湿度下液相反应的加剧,NO_(3)^(-)、SO_(4)^(2-)和NH_(4)^(+)细粒子峰由0.65-1.1μm向1.1-2.1μm粒径段转移.Ca^(2+)、Mg^(2+)和Na^(+)主要集中在粗模态中,自然源对沙尘污染贡献显著;K^(+)和Cl^(-)沙尘阶段呈明显双峰型分布;OC和EC主要呈双模态分布,不同阶段峰值出现的粒径段有所改变.重污染阶段消光系数大值区主要位于1.0 km以下;边界层高度0.5 km左右且伴随有下沉气流,持续的偏东风或偏南风有利于大气增湿及污染物区域输送共同导致此次污染过程污染物持续升高.本研究可为成都市大气颗粒物形成的化学和物理机制的深入研究提供基础资料.

The atmospheric particles in Chengdu were continuously sampled from December 15^(th),2017 to January 3^(rd),2018 by using 8-stage sampler(Andersen).Meteorological observation data and aerosol lidar data were used to analyze the particle size distribution characteristics of water-soluble inorganic ions and carbonaceous aerosols and vertical distribution evolution of aerosol during the pollution process.The results showed that the formation and accumulation of secondary aerosols were important reasons for the occurrence and development of this pollution process.NO_(3)^(-) and SO_(4)^(2-) were unimodal during the heavy pollution period,peaking at 0.65-1.1μm,suggesting that they were mainly from in-cloud process.NO_(3)^(-) and SO_(4)^(2-) showed a bimodal distribution during the dust period and the main peak was 3._(3)^(-)4.7μm.,suggesting that NO_(3)^(-)was formed mainly heterogeneous reactions in the coarse particles and SO_(4)^(2-) was from both primary pollution sources(dust,soil sources,etc)and secondary oxidation reactions.Owing to high humidity,the aqueous phase reactions of NO_(3)^(−),SO_(4)^(2-)and NH_(4)^(+) were likely promoted,which led to the peak shifted from 0.65-1.1μm to 1.1-2.1μm.Ca^(2+),Mg^(2+) and Na^(+) were mainly concentrated in coarse particles,suggesting that natural sources contribute significantly to dust pollution.The size distribution of K^(+) and Cl^(-) were bimodal obviously during the dust period.OC and EC were bimodal mainly,and range of peak values were different during the different periods.The large value area of extinction coefficient during the heavy pollution period was mainly below 1.0 km.The boundary layer height was about 0.5 km and accompanied by downdraft airflow,and the continuous easterly or southerly wind were conductive to atmospheric humidification and regional transport of pollutants,which jointly lead to the continuous increase of pollutants in the pollution process.The study can provide basic data for further study on the chemical and physical formation mechanism of atmospheric particulate matter in Chengdu.