北京夏季灰霾天臭氧近地层垂直分布与边界层结构分析

The vertical distribution of ozone and boundary layer structure analysis during summer haze in Beijing

后奥运时期首都北京的空气质量被更加关注,尤其是对于灰霾天与光化学复合污染的状况,而近地层数百米高度内的大气污染物与大气物理参数垂直分布观测对于空气质量变化过程评估至关重要.因此,本研究于2009年8月1—16日,在北京市325m气象塔进行了相应的立体观测,观测平台垂直分布在距离地面高度8、47、120和280m四层中.同时,在近地面320m高度以内,分15层分别观测了大气温度、湿度、风速、风向.另外,使用气溶胶后向散射云高仪观测了边界层2.5km内气溶胶后向散射系数.利用垂直分层的O3数据与边界层物理观测数据并结合天气形势、后向轨迹模式等方法,综合分析了本次观测数据之间的相互关系和内在联系.结果表明:夏季西北部低压槽控制的北京区域不利于低空大气扩散,容易形成光化学污染叠加灰霾污染,污染形成时白天地面小时最大φ(O3)可达120×10-9,280m高度处可达155×10-9;来自西北偏西的气流一般较为干净,有利于北京污染物的清除,而来自西南和偏南的气流使北京的O3污染加重,导致区域性高浓度O3污染;在稳定天气条件下,夜间残留层与地面的φ(O3)差别越大,次日光化学生成的φ(O3)起点越高,表明残留层O3在次日混合层抬升过程中卷夹到地面,影响地面空气质量;300m以内的近地层,在50m高度左右存在φ(O3)变化程度剧烈层,这是城市冠层界面与大气化学反应共同作用的结果.

We observed the ozone profile and atmospheric boundary layer physical parameters from August 1, 2009 to August 16, 2009, in the 325 meters meteorological tower in Beijing. Four layers observation platform for ozone profile were distributed in 8 m, 47 m, 120 m and 280 m, and 15 layers for the atmospheric temperature, humidity, wind speed, and wind direction from the ground to 320 m high. Ceilometer CL31 was used to provide information on the particles backscatter properties of the atmosphere in 2.5km height. By investigating ozone profile data, boundary layer physical parameters, the synoptic analysis, back trajectory analysis and photochemical smoke production model, the inter- and intra-relationship of the observation data was comprehensively analyzed. It was concluded that when Beijing area was controlled by northwest trough of low pressure in the summer, the low level atmospheric diffusivity was weak, favoring photochemical reaction and haze pollution. When pollution was formed, the highest ground-level hourly φ（O3） in the daytime can reach up to 120×10^-9 and φ（O3） can reach 155×10^-9 on 280 meters. West or northwest wind normally brought clean air mass and was helpful in removing pollutants in Beijing, while the airflow from southwest or south aggravated photochemical pollution in Beijing, leading to regional haze. During the stable weather conditions, the bigger difference of φ（O3） level between residual layer and the ground, the higher base level of photochemical generation in next day. This showed that O3 in residual layer was rolled into the ground that influenced the ground air quality during mixing layer uplifting process. There was an intense φ（O3） change layer about 50 meters high as a result of the canopy interface within city and atmospheric chemical reaction.