Trends in Air Pollutant Concentrations and the Impact of Meteorology in Shandong Province, Coastal China, during 2013-2019

摘要

Although weather conditions significantly affect air pollutant concentrations, few quantitative studies have been conducted on the effects of long-term and seasonal changes in meteorology on air quality. Hence, in this study, the trends in Shandong Province, China, for six criteria pollutants (viz., sulfur dioxide [SO2], carbon monoxide [CO], particulate matter [PM] with an aerodynamic diameter of < 10 μm [PM10], PM with an aerodynamic diameter of < 2.5 μm [PM2.5], nitrogen dioxide [NO2], and ozone [O3]) were analyzed for the period of 2013–2019, when overall emissions of air pollutants decreased, and the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem) was applied to evaluate the role of inter-annual and seasonal meteorological changes. Five of the six criteria pollutants exhibited a sharp drop in concentration until 2017 and a gradual decline afterward, with the maximum and minimum annual values occurring during winter and summer, respectively. In contrast, the level of O3 rose between 2013 and 2019 and displayed the opposite seasonal trend. Also, the diurnal concentrations of the first five criteria pollutants showed a typical bimodal distribution, whereas those of the O3 showed a typical unimodal distribution. Furthermore, a trimodal distribution was observed for the ratios between the diurnal PM2.5 and PM10 concentrations. Using 2013 as the baseline, the inter-annual meteorological changes accounted for only 3.4–18.6% of the decrease in the five criteria pollutants—with little effect on the O3—between 2015 and 2019, indicating that emission control measures drove the long-term improvement in air quality during these years. However, seasonal meteorological factors, which favored diffusion during summer and winter but accumulation during spring and autumn, played a larger role in the short term for all six species, especially during winter, when they reduced concentrations (excluding those of SO2 in 2019 and O3 altogether) by 6.5–31.0%.