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With rapid economic growth and urbanization,the Yangtze River Delta (YRD) region in China has experienced serious air pollution challenges.In this study,we analyzed the air pollution characteristics and their relationship with emissions and meteorology in the YRD region during 2014-2016.In recent years,the concentrations of all air pollutants,except O3,decreased.Spatially,the PM2.5,PM10,SO2,and CO concentrations were higher in the north YRD region,and NO2 and O3 were higher in the central YRD region.Based on the number of non-attainment days (i.e.,days with air quality index greater than 100),PM2.5 was the largest contributor to air pollution in the YRD region,followed by O3,PM10,and NO2.However,particulate matter pollution has declined gradually,while O3 pollution worsened.Meteorological conditions mainly influenced day-to-day variations in pollutant concentrations.PM2.5 concentration was inversely related to wind speed,while O3 concentration was positively correlated with temperature and negatively correlated with relative humidity.The air quality improvement in recent years was mainly attributed to emission reductions.During 2014-2016,PM2.5,PM10,SO2,NOx,CO,NH3,and volatile organic compound (VOC) emissions in the YRD region were reduced by 26.3％,29.2％,32.4％,8.1％,15.9％,4.5％,and 0.3％,respectively.Regional transport also contributed to the air pollution.During regional haze periods,pollutants from North China and East China aggravated the pollution in the YRD region.Our findings suggest that emission reduction and regional joint prevention and control helped to improve the air quality in the YRD region.