• 关键词：北京重污染  天气形势  污染成因  高压系统  细颗粒物PM_2.5

• 基金项目：中国科学院战略性先导科技专项（A类）（No.XDA19040203）；大气重污染成因与治理攻关项目（No.DQGG0209，DQGG0107，DQGG0304）

• 郝宏飞
• 1. 中国科学院大气物理研究所, 大气边界层物理和大气化学国家重点实验室, 北京 100029;2. 中国科学院大学, 北京 100049

• 杨婷
• 中国科学院大气物理研究所, 大气边界层物理和大气化学国家重点实验室, 北京 100029

• 王自发
• 中国科学院大气物理研究所, 大气边界层物理和大气化学国家重点实验室, 北京 100029

• 郑海涛
• 1. 中国科学院大气物理研究所, 大气边界层物理和大气化学国家重点实验室, 北京 100029;2. 中国科学院大学, 北京 100049

• 摘要：我国重污染呈现愈演愈烈态势，重污染事件在供暖季节（污染频发期）尤为频发.本文利用北京2013—2015年采暖期逐小时PM_2.5浓度数据、再分析资料、气团后向轨迹、气溶胶雷达数据以及探空数据综合分析了北京地区重污染状况，概括了重污染发生时常见的天气形势，探讨了重污染形成原因与天气形势的关系.研究结果表明：2013—2015年采暖期北京发生重污染（日均PM_2.5浓度大于150 μg·m^-3）的天数分别为36、28及35 d，即北京采暖期21.9%的天数受重污染天气影响.2月份重污染事件最为频发，发生频次为27.3%.北京发生重污染事件时，地面被高压控制时，高空500 hPa多东移的槽脊，当位于脊后槽前时，为上升运动，西南风，850 hPa多暖平流，西南风输送暖湿气流，湿度较大，地面偏南风，可能会存在污染物的输送；地面为低压控制时，500 hPa一般为稳定的西风气流或西北气流，低空850 hPa可能存在暖平流，地面常伴随弱的风场辐合，导致污染物累积；当地面为均压场时，高空500 hPa多为脊后槽前的形势，低空无明显冷暖平流，地面等压线稀疏或无等压线，静风天气.这3类结构引发的重污染天数分别占总重污染天数的47.3%、18.2%及34.5%.进一步分析重污染成因与天气形势关系表明：北京地面受高压系统控制时，污染时间持续最长，也最为频发（47.3%），PM_2.5平均浓度最高可达258.8 μg·m^-3，且常伴随来自西南方向的污染物输送，北京上空1 km附近存在逆温和逆湿.对污染传输路径研究发现：主要存在3条输送通道，①天津-廊坊-北京、②沧州-廊坊-北京、③石家庄-保定-北京.鉴于目前数值模式对天气形势的预报较为成熟，本文对区域重污染过程与天气形势之间的关系研究，有助于为北京地区空气质量的精准预报预警提供科学支持.

• Abstract：Air pollution is a severe problem in China especially during heating season for the decade years. To investigate the formation mechanisms of air pollution during heating, the relationship between air pollution and synoptic pattern was explored by employed three-year (2013-2015) high resolution PM_2.5 concentrations, reanalyzed data, radiosonde data, sounding data and HYSPLIT Trajectory Model in megacity Beijing, China. The results indicated that heavy pollution days (daily PM_2.5 concentration > 150 μg·m^-3) during heating Beijing is 36, 28 and 35 for 2013, 2014 and 2015, respectively, namely, 21.9 percent of the days in autumn and winter affected by heavy pollution, especially February being the worst, up to 27.3 percent in this month. Consistent air pollution episodes always accompanied with the following synoptic patterns:When the surface often with south wind is controlled by anticyclone,groove and ridge occurs frequently at 500 hPa;when located in front of groove and behind ridge, it is the upward movement,and wind direction is southwest.At 850 hPa, there is mostly warm advection,which transports warm and moist airflows to Beijing, where humidity increases. When the surface with wind convergence is controlled by cyclone, at 500 hPa, it's stable west or northwest airflows;there may be warm advection at 850 hPa. When the surface with calm wind is controlled by uniform pressure,at 500 hPa,Beijing is located behind weak ridge, and there is no obvious cold and warm advection in the low air, with sparse pressure lines or none. On surface, Beijing was controlled by anticyclone, low pressure or uniform pressure situation, which accounted for 47.3%,18.2% and 34.5% of the serious haze episodes, respectively. The above results also illustrated that air pollution episodes accompanied with anticyclone arose most frequently with maximum daily PM_2.5 concentration 258.8 μg·m^-3, which is often accompanied by pollutants from the southwest, and there is an inversion and reverse humidity around 1 km above Beijing. Research on pollution transport finds that there are three main transport pathways:Tianjin-Langfang-Beijing, Cangzhou-Langfang-Beijing, and Shijiazhuang-Baoding-Beijing. Given it is very mature for synoptic situation forecast by numerical model, in this paper, the relationship between regional heavy pollution process and synoptic situation is analyzed, which offers scientific support for the accurate forecast and early warning of air quality in Beijing.

• Key words：Beijing air pollution  synoptic pattern  formation mechanisms  anticyclone  PM_2.5

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