中国东部春季一次强冷锋活动空气污染输送过程分析

利用CMAQ(4.7.1)和HYSPLIT后向轨迹模式,结合长岛和洪泽湖站点污染物观测数据,对2011年3月31日—4月3日影响我国东北部地区的一次典型强冷锋天气空气污染过程进行模拟分析,验证表明模式能较好地模拟此次强冷锋过程. 由结果可知,此次强冷锋前后污染物浓度呈先升后降又上升的现象. 在冷锋移动过程中,锋前出现一条高浓度污染带,锋面将污染物抬升至800～500 hPa的高度,使污染物在对流层中层快速向西太平洋传输；冷锋对当地污染物的去除不仅有水平方向的推动作用,还会使污染物向高空输送. 锋面过后污染物浓度急剧降低,冷锋对长岛站点SO₂、O₃、NO_x、PM_2.5的清除率分别为90.87%、34.10%、50.56%、72.69%,对洪泽湖站点则分别为82.53%、50.45%、65.11%、36.80%. 锋面过去1~2 d后,高压控制天气形势下污染物再次开始积累、浓度回升. 冷锋前后污染物形成一个“积累—锋前抬升—高空平流输送—锋后大风清除—积累”的循环. 

Process Analysis about the Impact of a Strong Cold Front on Air Pollution Transportation in Eastern China in Spring

In this paper, a variety of modeling tools including CMAQ and HYSPLIT models combined with the intensive monitoring data have been employed to simulate the air pollution processes of a typical strong cold front moving across northeastern China from 31th March to 3rd April, 2011. Compared to the observed data from the site of Changdao, Hongze Lake and other monitoring sites, CMAQ modeling system demonstrated it's ability to simulate the air concentration process of the cold front as well as regional concentration distribution. Both surface monitoring data and modeling results showed high concentration of air pollution before the cold front and drastically decrease after the front moved through. The cold front uplifted the pollutants to the height range of 800-500 hPa and the pollutants were quickly transported in the middle troposphere to the west Pacific. The air concentration was not only diluted by the horizontal advective transportation of the strong wind behind cold front, but was also raised up to the high altitude by the convective transport/diffusion before the cold front. Concentrations of SO₂, O₃, NO_x, PM_2.5 at Changdao site decreased 90.87%, 34.10%, 50.56%, 72.69% respectively while concentrations of SO₂, O₃, NO_x, PM2.5 at Hongze Lake decreased 82.53%, 50.45%, 65.11%, 36.80% respectively. Under the high pressure behind the cold front, air pollutants accumulated and concentrations rebounded again. For a complete cold front process, air pollutants may experience a cycle of “local accumulation-rising ahead of front-advective transport in the upper air-diluted by the strong gust of the wind-local accumulation”.