1.School of Environmental Science and Engineering, Nanjing University of Information Science &2.Technology
Due to the special terrain conditions and coal-based energy structure, air pollution in the Fenwei Plain has been a serious issue. In 2018, the Fenwei Plain was listed as a key area for air pollution prevention and control. This study used the observed concentrations of PM10, PM2.5, SO2, NO2, CO, O3 over 2015–2019 and the Air Quality Index (AQI) to analyze the temporal and spatial distributions of AQI and mass concentrations of pollutants in the Fenwei Plain. We applied the multiple linear regression model to identify the meteorological conditions that influenced the daily and interannual variations of PM2.5 in winter and the maximum daily average 8-hour O3 (MDA8_O3) in summer in the Fenwei Plain. We found that air quality of the Fenwei Plain deteriorated year by year from 2015 to 2017 but improved from 2018 to 2019. The most polluted cities were Xi’an, Weinan, Xianyang, Linfen, Yuncheng, Sanmenxia, Luoyang, which were located in the junction of the Fenhe plain and the Weihe plain. The primary air pollutants in the Fenwei Plain were PM2.5, PM10 or O3, which accounted for about 90% of the polluted days. Severe pollution occurred mainly in the winter heating period when the weather conditions were unfavorable and the emissions of pollutants were large. In summer, concentrations of O3 in the Fenwei Plain increased over the past years. The most important meteorological parameter for daily variations of both PM2.5 in winter and MDA8_O3 in summer was 2-meter air temperature (T2M), with relative contributions of 45.5% and 35.3%, respectively. T2M was positively correlated with PM2.5 in winter and MDA8_O3 in summer. The second important meteorological parameter was 2-meter relative humidity (RH2M) for both PM2.5 in winter and MDA8_O3 in summer, with relative contributions of 41.5% (positive correlation) and 25.4% (negative correlation), respectively. With respect to interannual variations in PM2.5 in winter, the two most dominant meteorological parameters were T2M (43.6%) and RH2M (31.9%), which were both positively correlated with concentrations. Changes in meteorological conditions in winter over 2015–2019 had an effect of increasing PM2.5, which offset to some extent the decreases in emissions. With respect to interannual variations in summertime MDA8_O3, the two most dominant meteorological parameters were T2M (71.7%, positive correlation) and wind speed at 850 hPa (WS850, 16.3%, negative correlation). Changes in meteorological conditions in summer over 2015–2019 had an effect of increasing O3 (1.2 μg m-3 yr -1), which was a smaller effect compared to the increases in O3 (7.5 μg m-3 yr -1) caused by changes in anthropogenic emission. Our results indicate that air pollution in the Fenwei Plain is severe. Which the particulate pollution has not yet been resolved yet, it now also faces new challenges of ozone pollution. Considering that the Fenwei Plain is under influenced by Shaanxi, Shanxi, and Henan, it is necessary for the three provinces to joint prevention and control to improve the air quality in the Fenwei Plain.