安徽省臭氧污染特征及其气象成因

Characteristics and Meteorological Causes of Ozone Pollution in Anhui Province

自2013年起,中国采取了以降低PM2.5质量浓度为首要目标的大气污染防治措施。该措施的实施在颗粒物治理方面已取得显著的成效,但近地层臭氧(O3)污染问题却愈发突出。文中基于多源资料,结合气团后向轨迹分析与多种统计分析研究了2017—2019年安徽省O3污染的时空分布特征、O3污染形成的局地气象条件及输送路径。空间上,安徽省O3-8h超标天数北多南少、东多西少,空间差异显著;淮河以北和沿江东部为2个O3污染高发区,夏半年(4—9月)年均超标天数超过60 d;江南为O3污染低发区,年均超标天数不到10 d。2017—2019年,O3超标率的空间差异缩小。时间上,O3-8h浓度年变化呈双峰型分布,双峰分别位于6月和8月或9月;O3超标天数主要集中在夏半年,夏半年的O3-8h超标天数占全年O3-8h超标天数的95%,6月O3-8h超标率最高;O3浓度日变化为单峰型,谷值、峰值分别在07时和15时。根据4—9月的资料,导致O3-8h超标的局地气象条件为高温、低湿和微风,如日最高气温高于30℃(淮河以北)或28℃(江淮之间和沿江东部)、日最低相对湿度低于60%、风速2~4 m/s有利于O3污染形成。气温和相对湿度对O3-8h超标率的影响与地域有关。O3污染高发区的代表性城市O3输送路径分析结果表明,O3污染与不利的输送条件密切相关,主要输送路径包括东北方向和偏东方向。

Since 2013,China has started air pollution control measures with reducing PM2.5 concentration as the primary goal,and had achieved remarkable successes.However,the near surface ozone pollution was becoming more and more prominent.In summer,O3 is often the primary air pollutant in many cities.Based on multi-source data,combined with back-trajectory-cluster analysis and various statistical methods,we analyzed the temporal-spatial distribution of ozone pollution in Anhui Province,the major mete⁃orological factors and transport paths for the formation of ozone pollution.During 2017 to 2019,the number of ozone pollution days showed significant spatial and seasonal differences.It was more in the northern cities than in the southern cities and more in the eastern cities than in the western cities.From 2017 to 2019,spatial differences were reducing.There were two high ozone pollution areas with annual average ozone pollution days over 60 d,which were located in the north of Huai River and the area along east Yangtze River.The region south to Yangtze River was a low incidence area of ozone pollution,with the annual average ozone pollu⁃tion days less than 10 d.The annual change of O3-8h showed a bimodal distribution,with two peaks in June and August or Septem⁃ber,respectively,and the one in June was more prominent.Around 95%of ozone pollution occurred in the summer half year(April to September),with June having the highest rate of ozone pollution over standard.The diurnal variation of ozone concentration was unimodal,with the valley at 07:00 BT and the peak at 15:00 BT.Based on the data from April to September,the key meteorologi⁃cal factors for O3 pollution included high temperature,low humidity and gentle wind,e.g.the daily maximum temperature over 30℃(the region to the north of Huai River)or 28℃(region between the Yangtze River and Huai River and along the east Yang⁃tze River),the daily minimum relative humidity below 60%and wind speed between 2~4 m/s.The results of back-trajectory-clus⁃ter-statistic analysis for representative cities in the high ozone pollution areas indicated that the ozone pollution was closely related to the adverse transport conditions.The main transport paths for ozone in Anhui include northeast and easterly directions.