Fenwei Plain Air Quality and the Dominant Meteorological Parameters for Its Daily and Interannual Variations

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, PM_2.5, SO₂, NO₂, CO, and 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. A multiple linear regression model was applied to identify the meteorological conditions that influenced the daily and interannual variations of PM_2.5 in winter and the maximum daily average 8-hour O₃ (MDA8_O₃) in summer in the Fenwei Plain. Results reveal that the 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, and Luoyang, which were located at the junction of the Fenhe Plain and the Weihe Plain. The primary air pollutants in the Fenwei Plain were PM_2.5, PM₁₀, or O₃, which accounted for about 90% of the polluted days. Severe pollution occurred mainly in the winter heating period when weather conditions were unfavorable and the emissions of pollutants were large. In summer, O₃ concentrations in the Fenwei Plain increased over the past years. The most important meteorological parameter for the daily variations of both PM_2.5 in winter and MDA8_O₃ in summer was the 2-meter air temperature (T2M) with relative contributions of 45.5% and 35.3%, respectively. T2M was positively correlated with PM_2.5 in winter and MDA8_O₃ in summer. The second important meteorological parameter was the 2-meter relative humidity (RH2M) for both PM_2.5 in winter and MDA8_O₃ in summer with relative contributions of 41.5% (positive correlation) and 25.4% (negative correlation), respectively. With respect to the interannual variations in PM_2.5 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 PM_2.5, which offset the decreases in emissions to some extent. With respect to the 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 a ⁻¹), which was a smaller effect compared to the increases in O₃ (7.5 μg m⁻³ a ⁻¹) caused by the changes in the anthropogenic emission. This study’s results indicate that air pollution in the Fenwei Plain is severe. With the particulate pollution not yet resolved in the Fenwei Plain, 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 establish joint prevention and control to improve the air quality in the Fenwei Plain.