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A field campaign was conducted to study the PM2.5 and atmospheric gases and aerosol\'s components to evaluate the efficacy of radical measures implemented by the Chinese gov-ernment to improve air quality during the 2016 G20 Summit in Hangzhou China.The lower level of PM2.5 (32.48 ± 11.03 μg/m3) observed during the control period compared to pre-control and post-control periods showed that PM2.5 was alleviated by control policies.Based on the mass concentrations of particulate components,the emissions of PM2.5 from local sources including fossil fuel,coal combustion,industry and construction were effectively reduced,but non-exhaust emission was not reduced as effectively as expected.The accu-mulation of SNA (SO42-,NO3-,NH4+) was observed during the control period,due to the favourable synoptic weather conditions for photochemical reactions and heterogeneous hy-drolysis.Because of transboundary transport during the control period,air masses from remote areas contributed significantly to local PM2.5.Although,secondary organic carbon(OCsec) exhibited more sensitivity than primary organic carbon (OCpri) to control measures,and the increased nitrogen oxidation ratio (NOR) implied the regional transport of aged sec-ondary aerosols to the study area.Overall,the results from various approaches revealed that local pollution sources were kept under control,indicating that the implementation of miti-gation measures were helpful in improving the air quality of Hangzhou during G20 summit.To reduce ambient levels of PM2.5 further in Hangzhou,regional control policies may have to be taken so as to reduce the impact of long-range transport of air masses from inland China.