2017年春夏期间南京地区臭氧污染输送影响及潜在源区

Transport Influence and Potential Sources of Ozone Pollution for Nanjing During Spring and Summer in 2017

基于南京市空气质量数据与NCEP全球再分析资料,利用后向轨迹模式计算了2017年春夏(4~10月)到达南京城区逐时的24 h近地面气团后向轨迹,并将后向轨迹数据与臭氧质量浓度数据结合,进行轨迹聚类与潜在源区分析.结果表明,2017年南京市臭氧日最大8 h滑动平均浓度在12~261μg·m^(-3),超标共58 d,主要集中在春夏季.臭氧月变化呈现单峰状,其中6月臭氧浓度与超标天数最高,臭氧日变化总体呈单峰状,峰值浓度出现在14:00左右;模拟获得5136条轨迹,其中超标轨迹约占10%,超标轨迹月度分布差异较为明显,5、6两月合计占比约60%,经聚类分析得到气团输送路径共有6条,分别来自东北偏北、西北、西南、东南偏南、东南及东北方向,其中东南与东南偏南方向两类气团出现频率最高,分别为23.33%和20.76%,且对应的臭氧浓度较高,对南京臭氧污染贡献较大;潜在源区分析WPSCF与WCWT的高值区一致性较好,均揭示臭氧污染潜在源区主要分布在常州、无锡、苏州与湖州等环太湖城市,同时周边城市泰州、马鞍山、芜湖、滁州、南通与连云港等地是次要的潜在源区.臭氧污染区域输送贡献明显,需要强化长三角区域联防联控.

In this study,the 24-hour backward trajectories of air mass at ground level(10 m)in Nanjing were calculated by using the HYSPLIT model with the NCEP global reanalysis data from April 1st to October 31st,2017.The backward trajectories were then combined with the hourly concentration data of O3 in Nanjing for trajectories clustering analysis and potential pollution sources analysis.The results show that in 2017,the maximum daily 8 h running average O3 level in Nanjing was around 12-261μg·m^(-3)with 58 days of O3 pollution in Nanjing,mainly in the spring and summer.The monthly variation of O3 showed a single peak,with the highest O3 concentration,as well as the most days exceeding the standard,occurring in June;the diurnal variation of O3 was unimodal and reached its peak around 14:00.A total number of 5136 trajectories were obtained by simulation,among which the exceeded trajectories accounted for approximately 10%.The exceedance trajectories in May and June were significantly higher,accounting for 60%of the total exceedance trajectories.Six ground-level air mass transporting pathways were identified through clustering analysis,from the NNE,NW,SW,SSE,SE,and NE directions.The SE and SSE directions with higher O3 levels were the dominant transport routes of O3 pollution,contributing to 23.33%and 20.76%of backward trajectories,respectively.As for the potential pollution source analysis,the area with high WCWT value distribution matched the WPSCF result,indicating that the potential sources of O3 pollution were mainly distributed in Changzhou,Wuxi,Suzhou,Huzhou,and other cities around Taihu Lake.Additionally,cities located around Nanjing,such as Taizhou,Ma'anshan,Wuhu,Chuzhou,Nantong,and Lianyungang,were considered the secondary potential sources.The results indicate that O3 pollution in Nanjing is a regional issue and its control requires joint prevention and control strategies in the Yangtze River Delta.