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 (O₃) 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 O₃ observations in 223 cities. The observed maximum 1 h O₃ concentrations exceed 200 µg m⁻³ in almost all the cities, 400 µg m⁻³ in more than 25 % of the cities, and even 800 µg m⁻³ in six cities in eastern China. The average daily maximum 1 h O₃ concentrations are more than 160 µg m⁻³ in 45 % of the cities, and the 1 h O₃ concentrations of 200 µg 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 PM_2.5 from April to September in eastern China have considerably decreased, but the O₃ concentrations have increased by 9.9 %. A widespread and severe O₃ 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 O₃ contribution of biogenic and various anthropogenic sources. The model generally performs reasonably well in simulating the temporal variations and spatial distributions of near-surface O₃ concentrations. Using the factor separation approach, sensitivity studies have indicated that the industry source plays the most important role in the O₃ formation and constitutes the culprit of the severe O₃ pollution in eastern China. The transportation source contributes considerably to the O₃ formation, and the O₃ contribution of the residential source is not significant generally. The biogenic source provides a background O₃ source, and also plays an important role in the south of eastern China. Further model studies are needed to comprehensively investigate O₃ formation for supporting the design and implementation of O₃ 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