一次以南京为中心的夏季PM_(2.5)污染岛污染事件的数值模拟

2013年6月23~24日南京及其周边地区发生了一次小范围、突发性的气溶胶污染事件,PM_(2.5)的平均浓度达到242μg/m3,在夏季比较少见.本文利用WRF-chem模式对该PM_(2.5)污染事件进行模拟,通过对模式结果进行分析表明:此次污染事件与天气形势和边界层结构有着直接联系.此次污染发生时江淮地区正处于梅雨时节,南京及其周边地区处于江淮低空切变线上,切变线附近有辐合的流场,东部上游排放源的贡献和南京本地的静稳风场导致污染物在南京堆积.污染期间有比平时更强的气粒转化过程,23日PM_(2.5)浓度受到SO2减半的影响,浓度减少量为9.8%,受NOx减半影响的减少量为7.3%.污染发生期间南京地区上空温度垂直梯度较小,温度层结不利于污染物的垂直扩散,边界层高度较低,低层大气湍流活动较弱,垂直高度上的稳定层结也为污染物集聚提供了条件.

A numerical simulate study of the pollution incident of the PM2.5 pollutant island in the summer of Nanjing

A small scale, gusty aerosol pollution incident occurred from June 23 to 24, 2013 in Nanjing and its surrounding areas where the average concentration of PM_2.5 reached 242.25 μg/m³, which was uncommon in clear summer time. The WRF-chem model was used to simulate the PM_2.5 pollution incident and the results showed that the pollution incident was directly related to the weather situation and the boundary layer structure. The pollution occured in Jianghuai region during the rainy season with a Jianghuai low level shear line lay near the convergence of airflow in Nanjing and its surrounding areas. Emissions from the upstream source region in the east and the stable local wind field led to the accumulation of pollutants in Nanjing. There was a stronger gas-particle conversion and the concentration of PM_2.5 showed a decrease of 9.8% and 7.3% when SO₂ and NO_x emission was cut in half respectively. During the pollution period, the vertical temperature gradient was small over Nanjing and the temperature stratification was not conducive to the vertical diffusion of pollutants. As the boundary layer height was low and atmospheric turbulence in low layer was weak, the stable stratification was also favor of the pollutant accumulation.