北京地区平均最大混合层厚度的时间变化特征

Temporal Characteristics of Atmospheric Maximum Mixing Depth of Beijing

大气混合层厚度是大气环境质量影响预测中所需的重要参数。应用Holzworth干绝热法计算最大混合层厚度的基本原理,采用王式功等提出的逐步逼近法计算了北京观象台站1970—2007年的最大混合层厚度,分析了最大混合层厚度38年的变化和月平均值的年变化特征,同时应用2004—2007年同期的北京地区空气质量等级与同期大气混合层厚度逐月分布频率进行比较。结果表明,北京观象台的平均最大混合层厚度自1970—1998年有逐年减小趋势,1998年达到最小值,而从1998—2007年有逐年增加趋势,年平均最大混合层厚度与年降水日数有较为明显的负相关关系。最大混合层厚度的年变化表现出冬季低和夏季高的特征,且在夏季的7月和8月出现一个相对的低谷。空气质量等级与同期大气混合层厚度逐月分布频率表明,较高的最大混合层厚度出现频率较大的月,空气质量等级为1级和2级出现的频率高,而较低的最大混合层厚度出现频率较大的月,其空气质量等级为3级和4级出现的频率高。

Atmospheric mixing depth is one of most important parameters in air quality potential forecasting. Based on Holzworth＇s fundamental and Wang＇s stepwise approach,by using daily meteorological data from Beijing Observatory during 1970—2007,the maximum mixing depths（MMD） in Beijing Area were calculated and their variation characteristics with time were analyzed.The results showed that,from 1970 to 1998 the annual mean MMD had a decrease trend and got a minimum value in 1998,then from 1998 to 2007,the annual MMD turned into an increase trend.The seasonal variation showed the mean MMD being low in winter and high in summer.And the air quality and MMD frequency distribution revealed there is a remarkable negative correlation between them.