北京秋季一次典型大气污染过程多站点分析

Multi-Site Study of a Typical Autumn Air Pollution Event in Beijing

多站点多种大气污染物的同步在线观测对深入剖析大气污染的成因和演变机制有重要意义。以龙潭湖、北京325 m塔、双清路和阳坊4监测站点实时NOx、SO2、O3、PM2.5和PM10浓度观测数据为基础,介绍了北京地区2010年10月3~11日发生的一次典型污染过程。不同污染物在污染过程中变化特征不一致,表现为NOx、SO2、O3浓度有明显日变化,而PM浓度升高后一直维持在高值,日变化幅度很小。通过分析不同站点、相同污染物之间的相关性和变异系数发现,4站点间一次污染物NO和SO2空间浓度差别大,变异系数分别为77%和70%,相关系数低于0.44;而二次污染物NO2、PM2.5、O3空间浓度差别较小,变异系数分别为34%、36%和29%,相关系数均超过0.54。结合中尺度气象模式研究发现,该污染过程中,850 hPa高空持续的西南暖平流造成华北地区显著平流逆温,与近地层辐射逆温共同作用,使北京地区混合层高度维持在1200 m以下。低混合层高度和低风速限制了大气垂直和水平扩散,造成北京地区近地层污染物累积,形成重度污染。

Synchronous online observations of multiple sites and species are significant for in-depth analysis of the causes and evolution mechanism of air pollution. In this study, the authors analyzed a typical air pollution event that occurred during 3-11 October 2010, on the basis of NOx, SO2, O3, PM2.5, and PM10 levels recorded at four monitoring sites in Beijing. Variations of the pollutants were determined to be inconsistent, with concentrations of NOx, SO2, and O3 appearing as obvious diurnal variations and PM showing slight daily changes while maintaining high levels of concentration. Calculation of the correlation coefficient and coefficient of variation of concentration for these pollutants revealed the following results： The coefficients of variation for the primary pollutants of NO and SO2, with correlation coefficients of less than 0.44, were 77% secondary pollutants NO2, PM2.5, and and 70%, respectively, exhibiting 03, with correlation coefficients distinct spatial distribution. Those for the above 0.54, were 34%, 36%, and 29%,respectively, exhibiting consistent spatial distribution. These findings were applied to the Fifth-Generation Penn State/National Center for Atmospheric Research （NCAR） Mesoscale Model （MM5）, which revealed that advection inversions caused by continued southeast warm air flows at 825 hPa and radiation inversions near the ground induced the mixed layer at a height lower than 1200 m, which respectively hindered the atmospheric vertical and horizontal diffusions to result in the synchronous accumulation of air pollutants.