南昌市环境空气污染时空变化特征及影响因素研究

选取2014~2017年南昌市不同时间尺度AQI及主要空气污染物数据，利用GIS技术、神经网络分析、后向轨迹模型及地统计分析方法，分析了南昌市环境空气污染时空变化特征及影响因素。结果表明，南昌市近年来空气质量总体变化不大，空气质量等级以良为主，占全年比例为57%~61%。但首要污染物变化较大，即PM2.5比例显著下降，NO2和O3比例显著上升，PM10变化不大。南昌市空气污染季节变化显著，冬春季空气质量较差，以PM10、PM2.5污染为主，夏季空气质量最好，以O3污染为主。空气污染周变化以周末及周一污染较重、周四污染最轻，说明南昌市空气污染除了与群众出行习惯有关，还存在其他影响因素。南昌市空气质量日变化呈双峰型（9:00~11:00和20:00~22:00），主要受上、下班高峰期带来的交通尾气影响。南昌市空气污染空间变化呈典型的“郊区-市区”分布，其中AQI、PM10、PM2.5、SO2、NO2、CO值均以市区较高、郊区较低，而O3的空间分布规律正好相反，这主要与城区NOx排放较多，O3易与其迅速反应而消耗有关。后向轨迹聚类分析结果表明，来自本地的短轨迹气团占比高，对PM2.5、PM10、NO2、O3的影响大。气象因素上，PM2.5、PM10、NO2受相对湿度影响较大，O3受温度影响较大。

Spatiotemporal Distribution of Air Pollution and Its Impacted Factors in Nanchang City

Base on GIS, self-organizing map (SOM), back trajectory model and geostatistical method, this study investigates the spatiotemporal distribution of air pollution and its impacted factors in Nanchang City. For this purpose, the data of air quality index (AQI) and the main air pollutants in different time scales from 2014 to 2017 is selected, as well as the meteorological factors. Results show that the air quality of Nanchang City is not significantly improved in recent years. 51≤AQI≤100 is the main level of AQI with the ratios between 57% and 61%. But the primary pollutants are greatly changed, e.g. the number of polluted days of PM2.5 decrease, while the counterpart of NO2 and O3 increase. For seasonal variation, the air quality in Nanchang City is poor in winter and spring, with PM10 and PM2.5 as the primary pollutants. In comparison, the counterpart is good in summer, with O3 as the primary pollutant. The air quality is relatively bad on Monday and the weekends, and relatively good on Wednesdays and Thursday. It reveals that travel habit of people is not the only influence factor for the air quality in Nanchang City. The diurnal variation of air quality in Nanchang City shows a bimodal distribution peaked at 9:00-11:00 and 20:00-22:00, which is primarily related to the traffic exhaust during the rush hours. For spatial distribution, the air quality in Nanchang City is poor in the downtown area compared with that in the suburban area. Specifically, the concentrations of PM10, PM2.5, SO2, NO2, CO are higher in the downtown area. In contrary, O3 shows the higher concentration in the suburban area. Because there is more amount of NOx emission in the downtown area and O3 is easily consumed by rapid reaction with them. Back trajectories and cluster analysis suggest that the prevailing air masses were from the nearby area in Nanchang and PM10, PM2.5, NO2 and O3 pollution may mainly originate from these areas. Principal component analysis (PCA) demonstrates that the relative humidity and temperature is the main impact corresponding to the high concentration of PM2.5, PM10 and NO2 and the concentration of O3, respectively.