APEC前后北京几次静稳天气边界层特征对比分析

Comparative Analysis of Boundary Layer Characteristics During Stable Weather over Beijing Around APEC

对北京地区2014年11月3-11日APEC会议期间的大气扩散条件与2014年10月的4次雾-霾过程进行对比分析,表明APEC会议期间静稳天气指数略低于10月4次过程,具备一定的污染物积累潜势。数值模拟结果表明,对北京及周边地区污染排放的控制是APEC期间北京保持低水平气溶胶浓度的重要原因。周边地区污染物传输以及特殊地形条件下山谷风环流的日变化对北京地区污染物浓度的区域分布及演变有重要影响,夜间地形北风对近地面污染物有明显清除作用。相较于重污染天气,APEC期间气溶胶浓度低,温度效应小,山谷风环流明显,同时白天混合层高度上升幅度大,有利于污染物扩散。减排使气溶胶浓度减小,而低浓度气溶胶又使污染扩散条件进一步好转的相互反馈作用,是"APEC蓝"出现的主要原因。

Atmospheric dispersion conditions during the November Beijing Asia-Pacific Economic Coopera- tion （APEC） meeting are analyzed and compared with those in October when four fog haze processes oc- curred. Stable weather index （SWI） during APEC was slightly smaller than that during the four fog haze processes in October. Numerical simulations show that emission control of Beijing and its surrounding areas is the main reason for a low level of aerosol concentrations in Beijing during APEC. Both the pollu- tion transmission from neighboring regions and the diurnal variations of mountain-valley breeze under spe- cial terrain conditions contributed to the space distribution and time variation of pollution over Beijing. The north wind at night caused by topographic distribution eliminated pollution near ground obviously. Com- pared to heavy pollution weather, during the APEC, because of the low aerosol concentration and the cor- responding enlarged diurnal variations of surface air temperature, the valley wind circulation in the Beiiing area was obvious and hence enhanced daytime mixing layer height, producing more conductive conditions to spread the pollutants. Emission reduction led to low aerosol concentration which improved dispersion condition further, forming a negative feedback for pollutants to accumulate, contributing to ＂APEC blue＂ as well.