南京地区细颗粒物污染输送影响及潜在源区

Transport Influence and Potential Sources of PM_(2.5)Pollution for Nanjing

基于南京市空气质量数据和NCEP全球再分析资料,利用后向轨迹模式计算了2019年3月至2020年2月以南京城区为受体点的逐小时气团24 h后向轨迹,并将后向轨迹数据和PM_(2.5)浓度数据结合,进行轨迹聚类和潜在源区分析.结果表明,研究期间南京市ρ(PM_(2.5))平均值为(36±20)μg·m^(-3),超过国家二级标准限值的污染天数为17 d,ρ(PM_(2.5))的季节变化特征明显:冬季(49μg·m^(-3))>春季(42μg·m^(-3))>秋季(31μg·m^(-3))>夏季(24μg·m^(-3)),全年PM_(2.5)浓度和地面气压显著正相关,而跟气温、相对湿度、降水量和风速均为显著负相关关系;春季气团输送路径为7条,其余季节均为6条,其中,春季的西北路和东南偏南路,秋季东南路和冬季西南路是各季主要的污染输送路径,均具有传输距离短,气团移动慢的特点,说明静稳天气下本地累积是PM_(2.5)出现高值的主要原因之一;冬季西北路气团传输路径较长,ρ(PM_(2.5))为58μg·m^(-3),是所有路径中第2高值,说明皖东北城市对南京输送影响较大;PSCF和CWT潜在源区分布较为一致,主要的潜在源区分布以南京本地和邻近区域为主,说明控制PM_(2.5)污染需要强化本地管控并和邻近区域开展联防联控,冬季污染输送影响最大,主要潜在源区分布在南京西北和滁州交界地带,且主要范围在滁州境内,联防联控的范围需要扩大到安徽.

In this study,24-hour backward trajectories of the air mass in Nanjing were calculated by using the HYSPLIT model with the NCEP global reanalysis data from March 2019 to February 2020.The backward trajectories combined with the hourly concentration data of PM_(2.5)were then utilized in the trajectory clustering analysis and potential pollution source analysis.The results showed that the average concentration of PM_(2.5)in Nanjing was(36±20)μg·m^(-3)during the study period,with 17 days exceeding the grade Ⅱ national ambient air quality standards(75μg·m^(-3)).PM_(2.5)concentration exhibited clear seasonal variation,with winter(49μg·m^(-3))>spring(42μg·m^(-3))>autumn(31μg·m^(-3))>summer(24μg·m^(-3)).PM_(2.5)concentration was significantly positively correlated with surface air pressure but significantly negatively correlated with air temperature,relative humidity,precipitation,and wind speed.Based on the trajectories,seven transport routes were identified in spring,and six routes for the other seasons.The northwest and south-southeast routes in spring,southeast route in autumn,and southwest route in winter were the main pollution transport routes in each season,with the characteristics of short transport distance and slow air mass movement,indicating that local accumulation was one of the main reasons for the high value of PM_(2.5)in quiet and stable weather.The distance of the northwest route in winter was large,and the PM_(2.5)concentration was 58μg·m^(-3),which was the 2^(nd)highest concentration in all routes,indicating that the cities in the northeast of Anhui had a great transport influence on Nanjing PM_(2.5).The distribution of PSCF and CWT was relatively consistent,and the main potential source areas were mainly local and adjacent areas of Nanjing,indicating that PM_(2.5)control is needed to strengthen local control and carry out joint prevention and control with adjacent areas.Winter was most affected by transport,its main potential source area was located at the junction of northwest Nanjing and Chuzhou,and the main source origin was in Chuzhou;therefore joint prevention and control should be expanded to Anhui.