Ambient PANs(peroxyacetyl nitrates)variation in Beijing from 2005 to 2010

Measurements for PANs by GC-ECD and other routine pollutants were taken in Beijing from 2005 and 2010.August was the typical photochemical season in Beijing urban sites.We compared monthly mean value and peak value,daily mean value and diurnal variation of PAN(peroxyacetyl nitrate)for the past six years in August.PAN monthly mean concentration was lowest in August,2005,about 500pptv.PAN increased gradually in 2006 and 2007 whose concentrations were 1413pptv and 2139pptv respectively.PAN concentration decreased to the level of 750pptv in 2008 and 2009.Persistent high PAN concentration occurred in August,2010 and the monthly mean value was as high as 6ppb.The diurnal variations were evident and positively single peaked.Seasonal variation for PAN was judged by measurements from Nov.2008 to Dec.2009.Concentation was higher in Winter.Thermal decomposition as the main loss path for PAN in the troposphere was not responsible for the concentration variation for these years in August. Correlation Analysis showed PAN had closer correlation with Ox(Ox=O3+NO2) than O3,and the high concentration of PAN was liable to have bigger correlation coefficient between PAN and O3.Backward trajectory clustering analysis proved that the air mass from south Beijing and the near districts around Beijing most influenced the PAN concentration and other pollutants. In the future, we will use principal component analysis and the multiple stepwise regression analysis to know the contribution variations from 2005 to 2010 for PAN's relevant factors including meteorologic parameters and SO2,CO,PM,NO,NO2, as well as to get the simple regression equation to predict the PAN concentration.