内蒙古呼包鄂区域冬季大气细颗粒物污染成因解析

Analysis of the Causes of Atmospheric Fine Particle Pollution in Winter in the Hohhot–Baotou–Ordos Area of Inner Mongolia

利用气象模式WRF和中科院大气所自主发展的大气气溶胶与大气化学模式IAP-AACM对2016年冬季内蒙古中部呼包鄂地区大气细颗粒物(PM2.5)的典型污染过程进行了模拟分析。结果表明,呼包鄂地区的空气质量变化主要受大范围天气形势影响。污染累积阶段,500 hPa高度上该区域受阻塞高压或弱高压脊前平直的偏西气流控制,地面为弱高压或均压场,风速较小,边界层高度低,污染物不易扩散,且气温和相对湿度较高,利于二次颗粒物生成;污染消散阶段,天气形势发生明显变化,550 hPa高度以下有强冷平流,地面易形成大风天气,利于污染物消散,伴随着冷空气的南下,下游地区的污染物也得到清除。呼包鄂区域PM2.5主要来源于本地排放,鄂尔多斯本地排放贡献大于60%,呼和浩特本地排放贡献大于80%,包头本地排放贡献达到90%,该区域空气质量的变化可以反映区域大气污染气象条件的变化。交叉相关分析发现,呼包鄂区域的PM2.5浓度与其下游的山西、河北、河南地区的PM2.5浓度具有高度的时间相关性,相位差在6~24小时。呼包鄂区域PM2.5污染的改善有赖于本地污染源的管控,该区域冬季空气质量变化可作为下游地区空气质量变化的前兆因子,有助于下游地区空气质量的预报预警。

Using the Weather Research and Forecasting model and the Aerosol and Atmospheric Chemistry Model developed by the Institute of Atmospheric Physics,Chinese Academy of Sciences,several typical pollution episodes of fine particulate matter(PM2.5)over the Hohhot-Baotou-Ordos area of Inner Mongolia in the winter of 2016 were analyzed.The results indicated that the air quality changes in the Hohhot-Baotou-Ordos area were mainly affected by the large-scale synoptic pattern.At the stage of pollution accumulation,at 500 hPa,this area was controlled by the flat westerly airflow in front of the blocking high pressure or weak high-pressure ridge.At the ground level,this area was located in the weak high-pressure or uniform-pressure field.The low wind speed and the low height of the boundary layer were unfavorable to pollutant dispersion.Meanwhile,the air temperature and relative humidity were high,which were conducive to the formation of secondary particles.At the stage of pollution dissipation,the synoptic patterns had significantly changed.Below 550 hPa,strong cold advection occurred,causing gale weather on the ground,which was beneficial to pollutant elimination.Cold air moved southward,and pollutants over downstream areas were removed.Local emission was the main source of PM2.5over the Hohhot-Baotou-Ordos area.Local emission accounted for over 60%,80%,and 90% of the air pollution in Ordos,Hohhot,and Baotou,respectively.The change in the air quality of these regions can reflect the change in regional air pollution meteorological conditions.Cross-correlation analysis showed that the PM2.5concentrations in Shanxi,Hebei,and Henan regions were correlated with those in Hohhot-Baotou-Ordos,with a phase difference of 6-24 hours.The improvement of PM2.5pollution in Hohhot-Baotou-Ordos depended on the control of local source emissions.In winter,the air quality change in this region can serve as an indicator of the air quality change in the downstream region,which is helpful for the prediction and early warning of air quality in the downstream region.