Effect of emission control measures on ozone concentrations in Hangzhou during G20 meeting in 2016

The effect of emission control measures on ozone (O₃) concentrations in Hangzhou during G20 (The Group of Twenty Finance Ministers and Central Bank Governors) meeting during 24 August to 6 September of 2016 was evaluated using the nested version of a global chemical transport model. During G20, observed concentrations of PM₁₀, PM_2.5, SO₂, NO₂, and CO were all below national air quality standards, whereas those of MDA8 O₃ were above national standard (with an averaged value of 160.2 μg m^-3) but had a decreasing trend. Model sensitivity studies show that, MDA8 O₃ concentrations in Hangzhou during G20 were reduced by 11.3 μg m^-3 (6.8%), 14.8 μg m^-3 (8.9%), and 19.5 μg m^-3 (11.7%) with emission control measures in the core area, Zhejiang province, and the Yangtze River Delta (YRD) region, respectively, indicating that control measures were the most effective when carried out jointly in YRD. Considering the ratios of NO_x to VOCs during G20, Hangzhou and most areas of Zhejiang province were in transitional regime; reductions in either NO_x or VOCs could reduce O₃ concentrations. We also quantified how sensitive O₃ concentrations respond to emission reductions in sectors of industry, power, residential and transportation in the whole of YRD during G20. The removal of emissions in industry and transportation sectors would lead to the largest reductions of 17.6 μg m^-3 (10.5%) and 12.3 μg m^-3 (7.4%) in MDA8 O₃ concentrations in Hangzhou during G20, respectively. This study has important implications for the control of high O₃ levels in eastern China.