• 关键词：环首都圈  霾和雾  长期变化  矢量和  气流停滞区  近地层输送

• 基金项目：国家重点基础研究发展计划项目（No.2011CB403403）

• 吴兑
• 1. 中国气象局广州热带海洋气象研究所, 广州 510080;2. 中国气象局北京城市气象研究所, 北京 100089;3. 中山大学环境科学与工程学院, 广州 510275

• 廖碧婷
• 广州市萝岗区气象局, 广州 510530

• 吴蒙
• 中山大学环境科学与工程学院, 广州 510275

• 陈慧忠
• 中国气象局广州热带海洋气象研究所, 广州 510080

• 王迎春
• 中国气象局北京城市气象研究所, 北京 100089

• 廖晓农
• 北京市气象台, 北京 100089

• 古月
• 北京市气象台, 北京 100089

• 张小玲
• 中国气象局北京城市气象研究所, 北京 100089

• 赵秀娟
• 中国气象局北京城市气象研究所, 北京 100089

• 权建农
• 北京市人工影响天气办公室, 北京 100089

• 刘伟东
• 北京市气象局, 北京 100089

• 孟金平
• 北京市气象局, 北京 100089

• 孙丹
• 北京市气象局, 北京 100089

• 摘要：为了研究环首都圈京津冀晋4省市霾和雾的长期变化特征与典型个例的近地层输送条件，使用京津冀晋长期气象资料和高分辨率自动气象站资料，分析了环首都圈霾和雾天气的长期变化趋势，与使用矢量和算法分析典型个例气流停滞区的形成过程.结果表明，在1950—1960年代，环首都圈京津冀晋4省市霾日非常少，1970年代开始增多，1980年代以后明显增多，并形成几个霾日集中区，比较明显的是邯郸-邢台-石家庄-保定-北京-天津的带状分布，还有太原及以南的带状分布，最为严重的情况出现在1996—2000年，2000年以后有一定减少.北京1950年代霾日比较多，最多达到1年有160 d以上霾日，与同期沙尘天气偏多相关联，随着在首都周边地区的大规模植树造林，到1967年，霾日已经减少到1年不足10 d，1970年代以后北京的能见度急剧恶化导致霾日迅速增加，到1980年代初增加到220 d以上，一直到1999年前后北京的霾日维持在每年160~200 d左右；2000年以后到北京奥运会前后，霾日持续下降，到2010年霾日仅有56 d，2012年有所反弹，增加到91 d.北京及华北地区霾日季节分布突出的特点是除去采暖季有较多的霾日外，在盛夏季节霾日也明显多，集中出现在6—9月，尤其是盛夏季节的7—8月，与所谓的桑拿天同期出现，这与全国大部分城市的变化趋势完全不同.霾过程的发生和矢量和的大小存在较为明显的正相关关系.霾过程中，在华北平原均出现明显的气流停滞区，区域矢量和很小，不利于空气中污染物的水平扩散；清洁过程时华北4省市尤其是北京地区受明显的西北气流影响，风矢量和为较一致的偏北方向，水平扩散条件较好，较利于污染物的扩散，对应同期能见度较高.京津冀西侧、北侧靠山、东邻渤海，尤其是北京小平原三面环山.太行山、燕山和军都山形成的“弓状山脉”对冷空气活动起到了阻挡和削弱作用，导致山前暖区空气流动性较小形成气流停滞区、污染物和水汽容易聚集从而有利于霾和雾的形成.由于受太行山的阻挡和背风坡气流下沉作用的影响，使得沿北京、保定、石家庄、邢台和邯郸一线的污染物不易扩散，形成一条西南-东北走向的高污染带，华北平原偏南气流的弱辐合作用和也加重了北京的污染.山西省的高浓度污染物亦在低空偏南气流输送下沿桑干河河谷和洋河河谷以及滹沱河-拒马河河谷向北京输送.河北中南部与山西诸河谷的累积污染带叠加近地层输送流场是造成北京严重霾天气过程的重要原因之一.

• Abstract：Based on the meteorological data and high-resolution automatic weather station data from 1950 to 2012, the long-term trend of haze and fog days and the surface layer transport conditions under haze weather in North China, including Beijing, Tianjin, Shanxi and Hebei, were characterized by using Vector Sum Technique. Results showed that the haze days were limited in the 1950s and 1960s, began to increase in the 1970s, and increased significantly after 1980s. A number of zones with severe haze occurrences were developed, represented by Handan-Xingtai-Shijiazhuang-Baoding-Beijing-Tianjin zone and the one from Taiyuan extending to the south. The number of haze days peaked in 1996—2000. The number of haze days was high in Beijing in the 1950s, with more than 160 days in the most serious year, mostly associated with dust storms. As a consequence of large-scale afforestation in its surrounding area, the haze days of Beijing dived to less than 10 per year from 1967. From the 1970s, the visibility of Beijing deteriorated sharply, with the number of haze days rose over 220 in the early 1980s, and maintained about 160~200 days per year until 1999. From 2000 to 2008, the haze days of Beijing began to decline. There were only 56 days in 2010, while rebounded to 91 days in 2012. Apart from the heating season, haze days also occurred frequently from June to September, especially from July to August. This seasonal characteristic was completely different from other parts of the country. Analysis using Vector Sum Technique showed that there was obvious positive correlation between regional haze process and the value of the vector sum. During the haze process, a significant airflow stagnation area was formed in the North China Plain, with a small value of regional vector sum that was not conducive to pollutant dispersion in the air. On the contrary, during the cleaning process, the prevailing wind was northwesterly, and vector sum was consistently northerly. This indicated that the horizontal diffusion conditions were conducive to pollutant dispersion, leading to a higher visibility. Beijing was confined on three sides by mountains, with Bohai Sea to the east. The "arcuate mountains" formed by Taihang Mountain, Yanshan Mountain and Jundu Mountain played an important role in blocking and weakening the activities of cold air, leading to the formation of air stagnation zone in the piedmont warm area. Pollutants and water vapor tended to accumulate, contributing to the formation of haze and fog. Due to the blockage of Taihang Mountain and the air sink along the leeward slope, the pollutants in the Beijing-Baoding-Shijiazhuang-Xingtai-Handan zone were difficult to diffuse, leading to a southwest-northeast serious pollution belt. High concentrations of pollutant over Shanxi were transported to Beijing by low-surface southerly flow along the Sanggan Valley, Yanghe Valley, and Hutuohe-Juma Valley. Superimposed cumulative pollution belt over Central and Southern Hebei and valleys of Shanxi with the transport flow near the ground was an important reason for the severe haze process.

• Key words：Beijing-Tianjin-Shanxi-Hebei  haze and fog  long-term trend  vector sum  airflow stagnation area  surface layer transport

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