南京市灰霾影响因子的数值模拟

Numerical Simulation of Impact Factors of Urban Haze in Nanjing Area

利用改进的南京大学空气质量预报系统(NJU-CAQPS),对2005年1月7日南京典型天气条件形成的污染过程进行了数值模拟,分析了城市人为热源、城市建筑物效应和不同类型人为热源排放对该区域主要污染物分布的贡献及对能见度造成的影响。结果表明,城区日平均能见度最低可达8km以下,一天之中有18h主城区地表能见度低于10km,属于典型灰霾天气;工业点源排放对地表SO2日平均浓度贡献最大,最大值达到110μg.m-3以上;流动源(即机动车源)排放对地表NO2日平均浓度贡献最大,最大值达到70μg.m-3以上;面源排放和点源排放对地表PM2.5日平均浓度贡献最大,最大值分别达到100μg.m-3和45μg.m-3以上。人为热源使低层大气温度升高、风场幅合,主城区垂直向上速度增大,从而降低了主城区地表污染物浓度,使能见度上升,灰霾影响面积减少了20.2km2。建筑物效应使主城区水平风速减小,污染物在主城区及上风方向聚集,浓度上升,在建筑物平均高度较高和密度较大的区域,细粒子PM2.5浓度比没有建筑物时约高10μg.m-3,相应地,主城区能见度下降,最大降幅可达2km,灰霾持续时间增加了2h,灰霾面积约增加了134km2。

Air pollution process in Nanjing on 7 January 2005 induced by typical weather condition was simulated with the modified Nanjing University City Air Quality Prediction System（NJU-CAQPS）.The contribution ratios of urban anthropogenic heat source,urban buildings and various anthropogenic heat sources to the concentration of several main pollutants and the impacts of the anthropogenic heat sources on visibility distribution were analyzed.The result shows that in main urban district,the daily average surface visibility reduced below 8 km,and the hourly surface visibility is less than 10 km for 18 h in one day;this condition should be considered as a heavy haze process.The industrial point source dominates mostly the daily average surface concentration of SO2,its peak value is above 110 μg·m-3;mobile source contributs the most to the daily average NO2 surface concentration,its peak value is above 70 μg·m-3;area and point sources have the significant contribution to the daily average surface concentration of PM2.5,the peak value is more than 100 μg·m-3 and 45 μg·m-3,respectively.Due to the anthropogenic heat source release, the lower layer temperature air increased and wind converged,the vertical speed over urban district increased,all these lead to the decreases of surface concentration of SO2,NO2,PM2.5 in urban district,the surface visibility increased correspondingly,and the area of regions over where visibility less than 10 km has decreased 20.2 km2.The horizontal wind speed over urban district decreased because of the building distribution,so that mass of pollutants concentrate over urban area and upper drift to the urban district,and in this district the concentration of various pollutants obviously increased.The concentration of fine particles（PM2.5） has increased 10 μg·m-3, comparing with the case without building effects. The comparison also showed that the ground visibility could decrease by a maximum of 2 km,the duration of visibility below 10 km increased by 2 hours,and the area of regions with haze increased by 134.2 km2 when the simulation concerned about the effects of buildings rather than not.