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The mass concentrations of PM10,PM2.5 and PM1 were investigated simultaneously in 24 stations of CAWNET (China Atmosphere Watch Network) from 2006 to 2012 using GRIMM 180 instruments.The highest PM mass were observed at the stations of Zhengzhou,XiAn and Gucheng in Hua Bei Plain (HBP) of N.China,which is the most serious hazy area of China.For example,the averaged PM10,PM2.5 and PM1 concentrations at Zhengzhou are 149.9,94.6 and 77.7 μg m?3,respectively.The second high PM region is in E.China,and then in S.China,with the Yangtze River Delta and the Pearl River Delta areas as their major body,respectively.According to the newest air quality standard of China with annual averaged PM10 and PM2.5 mass concentrations of 70 and 35 μg m?3,15 stations can meet the PM10 standard and only 7 stations (most are rural and remote stations) have concentration lower than the PM2.5 standard.Due to the large contribution of coarse mineral aerosol in N.China and more secondary aerosol formation in relative warm and humid areas of S.China,the ratios of PM2.5 to PM10 exhibit obviously increasing trend from north to south,with the highest value of 80 – 90% in the Yangtze River Delta area.In the stations near the Asian dust source,the ratios are normally less then 50%.The PM1 mass contributed most of PM2.5,accounting over 80% at the most stations.Seasonally,PM concentrations are normally highest in winter and lowest in summer at most stations,with obvious increasing in spring associated with the impact of sand and dust storm (SDS).The decreasing trend followed by increasing trend was observed at XiAn from 2006 to 2012,but the trends are not reproduceted at other stations.It indicates that there is no significant improvement or deterioration trend of air quality with PM in recent years in China.