Volatile organic compounds in China: Characteristics, sources and contributions to O3 pollution

Urban core with densely interleaved residential, commercial and transportation lands hosts intensive air pollutants emission and reaction. In recent years, photochemical ozone (O₃) pollution significantly intensifies in Chinese cities. To investigate the responsible in-situ chemistry, O₃ and its precursors and meteorological parameters were simultaneously measured in 10 megacities in China and at 10 sites in the Pearl River Delta region in summer. Moderate wind speeds, strong solar radiation and high temperature were observed in all cities, indicating favourable meteorological conditions for local O₃ formation. The highest O₃ level was found in Beijing, followed by Lanzhou and Wuhan, while relatively lower O₃ value was recorded in Chengdu and Shanghai. Photochemical box model simulations revealed that net O₃ production rate in Lanzhou was the largest, followed by Beijing, Wuhan and Chengdu, while it was the lowest in Shanghai. Besides, the O₃ formation was mainly controlled by volatile organic compounds (VOCs) in most cities, but co-limited by VOCs and nitrogen oxides in Lanzhou. Moreover, the dominant VOC groups contributing to O₃ formation were oxygenated VOCs (OVOCs) in Beijing and Wuhan, alkenes in Lanzhou, and aromatics and OVOCs in Shanghai and Chengdu. Source apportionment analysis identified six sources of O₃ precursors in these cities, including liquefied petroleum gas usage, diesel exhaust, gasoline exhaust, industrial emissions, solvent usage, and biogenic emissions. Gasoline exhaust dominated the O₃ formation in Beijing, and LPG usage and industrial emissions made comparable contributions in Lanzhou, while LPG usage and solvent usage played a leading role in Wuhan and Chengdu, respectively. The findings are helpful to mitigate O₃ pollution in China.