【摘要】 本文利用2013年6月至2015年10月北京南苑观象台两年多午后臭氧探空资料,初步分析了北京城区大气混合层内臭氧浓度的垂直分布规律以及典型天气条件下大气边界层臭氧的变化特征.主要结果有:（1）季节平均而言,地表至对流层中部（8km）的臭氧浓度在夏季最高,冬季最低,相差50¹30μg·m^-3,最大差异在边界层.总体而言,对流层臭氧浓度随高度有比较缓慢的增加,但是边界层内臭氧浓度的垂直结构随季节有比较大的差异:夏季混合层中部存在一个臭氧浓度极大值,这与夏季比较强的光化学生成臭氧有关;而在冬季地面臭氧浓度很低,平均值小于40μg·m^-3,说明冬季地面是臭氧很强的汇.（2）臭氧浓度季节内变率的季节差异也十分明显,夏季最大、冬季最小.季节内变率在从边界层向自由对流层过渡区域最小(夏季为24μg·m^-3,冬季仅为10μg·m^-3),在边界层内变率较大,夏季可达64μg·m^-3(冬季为30μg·m^-3),这也说明边界层化学过程明显影响臭氧浓度的变化.（3）我们从所有白天样本中严格筛选了部分混合层样本,并把臭氧浓度在由混合层向自由大气过渡时的垂直分布分成了三类,即臭氧浓度随高度增大（Ⅰ型）、减小（Ⅱ型）以及基本稳定不变（Ⅲ型）;臭氧垂直结构类型有明显的季节特征,夏季主要是Ⅱ型,而冬季则以Ⅰ型为主.（4）此外,我们还针对一些典型天气过程（强风、静稳雾天和PM2.5污染）边界层内臭氧的变化特征进行了分析,结果表明:强风切变产生的机械对流引起的充分混合,有利于高层臭氧向低层输送,使得混合层内臭氧浓度的垂直梯度明显减小,同时混合层高度较高,达3km以上;在高湿度静稳天气控制下,大气混合层较稳定,对北京上空污染物的垂直扩散十分不利:颗粒物浓度升高,削弱到达近地层的太阳辐射,从而降低臭氧的生成效率,混合层内臭氧浓度与混合层厚度都处于较低水平.更多还原

【Abstract】 Vertical distribution of ozone in the Mixing Layer（ML）and its variation in the AtmosphericBoundary Layer（ABL）over Beijing during typical weathers are investigated based on highresolution ozonesonde data during June 2013 through October 2015.Seasonal mean analyses show that ozone is highest in summer,and lowest in winter,with differences of 50¹30μg·m^-3 from the ground surface to the middle troposphere（8 km）and largest difference in the ABL.On the whole,ozone concentration increases slowly with altitude in the troposphere.But the ozone structure in the ABL varies greatly in different seasons:there exists an ozone peak in the ML in summer,which is caused by the enhanced photochemical product;in winter,however,ozone is extremely low in the surface layer with an average less than 40μg·m^-3,which suggests that there is a significant sink for ozone there.There exists also an obvious difference of intraseasonal ozone variability among different seasons,with the highest variation in summer and the lowest in winter.Intraseasonal variation shows its minimum in the transitional layer from the ABL to free troposphere(24μg·m^-3 in summer while only 10μg·m^-3 in winter),and is much higher in the boundary layer(64μg·m^-3 in summer while 30μg·m^-3 in winter),which suggests that chemical processes take a critical role in the ABL.Cases for typical ML structure are screened out of all the profiles and are classified into three types in respect of their ozone transition from the ML to the free atmosphere:increase（typeⅠ）,decrease（typeⅡ）and remain constant（typeⅢ）with altitude.The ozone profiles have obviously seasonal differences,with summer dominated by typeⅡ,and winter by type I.In addition,ozone variations in the boundary layer under some typical weather conditions are also analyzed,such as strong winds,MLs capped by stratocumulus cloud,rainy days,and heavy PM2.5 pollution.Strong winds can enhance vertical mixing by wind shear,which is in favor of bringing ozone-rich air from above to lower levels,leading to uniform ozone vertical distribution in the ML and thicker depth of the ML（larger than 3 km）.On the contrary,calm weathers with high humidity and weak wind tend to weaken the vertical diffusion of pollutants,and result in the higher concentration of particulate matters.In return,solar radiation is weak in the ABL,and so is ozone production efficiency.As a result,both the depth of the ML and its ozone concentration are very low.更多还原