长沙市气流传输特征及其对大气环境的影响分析

Characteristics of Airflow Trajectories and Its Impact on the Atmospheric Environment in Changsha City

利用HYSPLIT气流轨迹模型和GDAS全球资料同化系统数据,文章计算了长沙市2016-2019年区域逐时的72 h气流后向轨迹并进行了轨迹聚类,结合监测数据分析了大气污染物浓度及气象因子受气流传输的影响规律,进一步采用轨迹权重浓度分析(WCWT)识别了污染潜在源区。结果表明:长沙市PM2.5与NO2、SO2、CO均显著正相关,而O3与NO2、CO均显著负相关,且O3与PM2.5浓度分别与风速呈显著正、负相关关系。长沙市受东北方向气流影响显著,春、夏、秋和冬季其轨迹占比分别为50.1%、37.7%、82.1%和42.8%,不同气流传输类型影响下污染物浓度差异明显,颗粒物、NO2、CO在冬季受西南及西北气流影响时浓度较高,其他三季受东北方向短距离传输气流影响时浓度较高,四季O3和SO2分别受东北方向、南面沿海方向气流影响时浓度较高;另外,区域风速和温度受不同类型气流影响时也存在明显差别。WCWT分析表明,长沙市PM2.5潜在源区域主要集中在西北方向的陕西、山西,东北方向的河南以及东南方向的广东等部分区域,O3潜在源区域主要集中在东北方向的河南、河北、江苏、浙江以及西南方向的广西、广东部分区域,SO2、NO2及CO潜在源区域较为相似,在西北方向的宁夏、陕西、湖北沿线及南面的广东珠三角区域均存在贡献高值;污染物潜在源分布差异显示,长沙市NO2受西北燃煤排放影响相对较大,而CO受广东珠三角区域机动车排放影响相对较大,区域NOx对O3的滴定作用明显。

The Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model and data from global data assimilation system(GDAS)were used to calculate the 72 hours backward trajectories from 2016 to 2019 in Changsha City,the cluster analysis method was used to analyze the characteristics of the backward airflow trajectories and their effects on the air pollutants concentration and meteorological factors over Changsha in different seasons,combining with the hourly monitoring data during the same period in Changsha.Meanwhile,Weighted Concentration-Weighted Trajectory Analysis(WCWT)were utilized to calculate the potential source regions combining with hourly pollutant concentration data.The results showed that PM2.5 was positively correlated with NO2,SO2 and CO,while O3 was negatively correlated with NO2 and CO.The concentrations of O3 and PM2.5 were positively and negatively correlated with wind speed respectively.The northeast airflow affected Changsha significantly and the proportions were as follows:spring(50.1%),summer(37.7%),autumn(82.1%),winter(42.8%).The differences in the impacts of different seasons and different backward trajectories on air pollutants concentration and meteorological factors in Changsha were significant.The concentrations of particulate matter,NO2 and CO were relatively higher in winter when affected by southwest and northwest airflow,while in other seasons,the concentrations were relatively higher affected by northeast short-distance airflow.However,the concentrations of O3 and SO2 were relatively higher all year round when affected by airflow from northeast and south coastal respectively.WCWT analysis found that parts of Shaanxi,Shanxi,Henan and Guangdong were the main potential areas affecting PM2.5 in Changsha.The main potential areas affecting O3 in Changsha were located in parts of Henan,Hebei,Jiangsu,Zhejiang,Guangxi and Guangdong.The potential areas of SO2,NO2 and CO were similar,mainly located in parts of Ningxia,Shaanxi,Hubei and Pearl River Delta region.Further analysis indicates that NO2 was greatly affected by coal-fired emissions from the northwest,while CO is greatly affected by motor vehicle emissions from the Pearl River Delta.The titration of NOxplayed an important role in O3 pollution in Changsha.