兰州冬季大气污染来源分析

Analysis of Air Pollutant Transport in Winter in Lanzhou

利用WRF(天气研究与预报模式)输出的高分辨率气象数据驱动HYSPLIT_4.9(混合单粒子拉格朗日轨迹模式),结合PSCF(潜在源贡献因子)和CWT(权重浓度轨迹分析)模拟研究复杂地形下兰州城市尺度大气污染物局地输送特征、潜在源区及其对空气质量的影响.结果表明:2002—2008年影响兰州城区冬季12月空气质量的轨迹可分为5类,输送类型可分为城区内输送和城区外输送.第1、3类轨迹出现频率均大于20%且污染轨迹出现频率均大于38%,是污染物的主要输送路径,对应潜在源区为兰州城关区东北部和榆中县东部,这2个源区对ρ(PM10)的影响最大,对ρ(SO2)的影响最小,对ρ(PM10)、ρ(SO2)和ρ(NO2)的贡献分别超过200、80和60μg/m3.来自榆中县的第4类轨迹和兰州西固区的第5类轨迹易造成大气重污染,而来自皋兰县的第2类轨迹属于清洁轨迹.兰州冬季污染既受局地输送的影响,也与地面天气形势密切相关.

The Hybrid Single Particle Lagrangian Integrated Trajectory （HYSPLIT） model, using high resolution meteorological fields from the Weather Research and Forecasting （WRF） model as an input, was used to analyze the pollutant transport characteristics and identify the main transport pathways by clustering 6 h backward trajectories for Lanzhou. Source regions and their relative contributions were defined with potential source contribution function （PSCF） and concentration-weighted trajectory （CWT）. The results indicated that trajectories could be grouped into five clusters for Decembers 2002-2008. The short-distance urban transport pathway from the northeast of the urban center and the east county transport pathway together accounted for more than 20% of all trajectories and 38% of all polluted trajectories. These were the most important pathways leading to high pollutant concentrations in Lanzhou during Dece 2002- 2008. The potential source areas were located in Chengguan District in the urban center and Yuzhong County. The effects of potential source areas on PM10 loadings were higher than on SO2 and NO2 , with the least effects on SO2. The contributions of the two potential source regions to PM10, SO2 and NO2 loadings were more than 200, 80 and 60 μg/m^3, respectively. The long-distance transport pathways from Yuzhong County and Xigu District tended to cause high pollution events in Lanzhou. The trajectories from Gaolan County were relatively clean. The air pollution in Lanzhou was affected by local transportation processes, but was also related to the weather situation.