Widespread and persistent ozone pollution in eastern China during the non-winter season of 2015: observations and source attributions

Rapid growth of industrialization, transportation, and urbanization has caused increasing emissions of ozone (O-3) precursors recently, enhancing the O3 formation in eastern China. We show here that eastern China has experienced widespread and persistent O3 pollution from April to September 2015 based on the O-3 observations in 223 cities. The observed maximum 1 h O-3 concentrations exceed 200 mu g m(-3) in almost all the cities, 400 mu g m(-3) in more than 25% of the cities, and even 800 mu g m(-3) in six cities in eastern China. The average daily maximum 1 h O-3 concentrations are more than 160 mu g m(-3) in 45% of the cities, and the 1 h O-3 concentrations of 200 mu g m(-3) have been exceeded on over 10% of days from April to September in 129 cities. Analyses of pollutant observations from 2013 to 2015 have shown that the concentrations of CO, SO2, NO2, and PM2.5 from April to September in eastern China have considerably decreased, but the O-3 concentrations have increased by 9.9 %. A widespread and severe O-3 pollution episode from 22 to 28 May 2015 in eastern China has been simulated using the Weather Research and Forecasting model coupled to chemistry (WRF-CHEM) to evaluate the O-3 contribution of biogenic and various anthropogenic sources. The model generally performs reasonably well in simulating the temporal variations and spatial distributions of near-surface O-3 concentrations. Using the factor separation approach, sensitivity studies have indicated that the industry source plays the most important role in the O-3 formation and constitutes the culprit of the severe O-3 pollution in eastern China. The transportation source contributes considerably to the O-3 formation, and the O-3 contribution of the residential source is not significant generally. The biogenic source provides a background O-3 source, and also plays an important role in the south of eastern China. Further model studies are needed to comprehensively investigate O-3 formation for supporting the design and implementation of O-3 control strategies, considering rapid changes of emission inventories and photolysis caused by the Atmospheric Pollution Prevention and Control Action Plan released by the Chinese State Council in 2013.