乌鲁木齐大气最大混合层厚度变化的环境响应

Envirenmental Response to Variation of the Atmospheric Maximum Mixing Depth in Urumqi

应用Holzworth干绝热曲线法求最大混合层厚度的基本原理,利用逐步逼近法和乌鲁木齐市气象站2003年1月至2009年4月逐日的气象观测资料,计算并分析了乌鲁木齐市大气最大混合层厚度的时间变化及其与空气污染的关系。结果表明:乌鲁木齐大气最大混合层厚度月均值的年变化呈单周期型,即1月最低(389 m),6月最高(2 071 m);4～9月大气最大混合层厚度在2 000 m以上的出现频率超过50%,冬季11月至次年2月则是500 m以下出现频率最大。乌鲁木齐大气污染指数与最大混合层厚度呈显著的负相关关系,表明最大混合层厚度是影响城市空气污染的重要因素。逐日PM10浓度与对应最大混合层厚度存在指数关系。

It is well known that Urumqi is one of the cities with the severest air pollution in China and even over the world.A large numbers of researches on calculation methods of maximum mixing depth（MMD） and relations between MMD and air pollutant concentration have been performed in the world in recent 50 years.However,there have been only a few studies focusing on the characteristics of MMD over Urumqi and the impacts of MMD on local air quality so far.According to the fundamentals of estimating MMD by the assumption of a dry adiabatic lapse rate and method of stepwise approach,in this paper the MMD values in Urumqi were calculated and their variable characteristics and relations with air pollution were analyzed based on the daily surface and sounding meteorological data observed during the period from January 2003 to April 2009.The result reveals that the annual change of monthly mean MMD was singly periodic.That is,the minimum value（389 m） of monthly mean MMD occurred in January but the maximum value（2 071 m） occurred in June.The occurrence frequency of MMD over 2 000 m during the period from April to September was higher than 50%.Moreover,the occurrence frequency of MMD below 500 m during the period from November to next February was relatively high.There was a negative correlation between air pollution index and MMD.As the air pollution level was increased,the MMD values with peak occurrence frequency was correspondingly decreased,that is,the MMD is one of the important factors affecting local air pollution,and there is an exponential relation between the daily mean PM10 concentration and the MMD.