Temporal variations in ambient air quality indicators in Shanghai municipality, China.

Official data on daily PM, PM, SO, NO, CO, and maximum 8-h average O (O_8h) concentrations from January 2015 to December 2018 were evaluated and air pollution status and dynamics in Shanghai municipality were examined. Factors affecting air quality, including meteorological factors and socio-economic indicators, were analyzed. The main findings were that: (1) Overall air quality status in Shanghai municipality has improved and number of days meeting 'Chinese ambient air quality standards' (CAAQS) Grade II has increased. (2) The most frequent major pollutant in Shanghai municipality is O (which exceeded the standard on 110 days in 2015, 84 days in 2016, 126 days in 2017, 113 days in 2018), followed by PM (120days in 2015, 104 days in 2016, 67 days in 2017, 61 days in 2018) and NO (50 days in 2015, 67 days in 2016, 79 days in 2017, 63 days in 2018). (3) PM pollution in winter and O pollution in summer are the main air quality challenges in Shanghai municipality. (4) Statistical analysis suggested that PM, PM, SO and NO concentrations were significantly negatively associated with precipitation (Prec) and atmosphere temperature (T) (p < 0.05), while the O concentration was significantly positively associated with Prec and T (p < 0.05). Lower accumulation of PM, SO, NO, and CO and more serious O pollution were revealed during months with higher temperature and more precipitation in Shanghai. The correlation between the socio-economic factors and the air pollutants suggest that further rigorous measures are needed to control PM and that further studies are needed to identify O formation mechanisms and control strategies. The results provide scientific insights into meteorological factors and socio-economic indicators influencing air pollution in Shanghai.