Haze Variations And Connecting Tactors Over The Yangtze River Delta Region

With the rapid development of urbanization and industrization, the Yangtze River Delta region has suffered low visibility and haze episodes..It is typical to analyze extinction coefficient of visibility,meteorological condition and physical and chemical characteristics of aerosols in Nanjing during haze.It is crucial to compare the difference and applicability of different haze discrimination methods and its criteria in haze study based on the meteorological data from38observation stations of year1980-2009. Choose method3to obtain haze day of Yangtze River Delta region,The extinction coefficients for all observation sites were calculated with double correction.The corrected extinction coefficients varied seasonally from the peak in winter to the bottom in summer. According to the Chinese urban API (Air pollution Index) data of2000-2009, the relationship of visibility and air pollution over Nanjin,Hangzhou and Heifei are discussed. According to the data of scattering coefficient and absorption coefficient of aresols,PM2.5concentration and the ground observation,the contribution of extinction factor is analyzed. The stepwise regression model of visibility in different relative humidity are calculated. Nanjing suffered heavy haze in December2013.Based on the ground observation data,sounding data,surface chart and on-line measurement of chemical compositions system,the cause of this heavy haze was analyzed.The results showed that Method1and2(with daily mean observation) and Method3(with14:00observation) are all capable to represent the long-term trend of haze, but haze-day numbers counted via these methods show differences, which becomee less remarkable with decadal changes, the haze-day number obtained employing Method3is less than others, while the haze-day number obtained employing Method4is between those with Method1and3; using all Methods but Method3can distinguish the severity of haze significantly.Over the30years, there was a significantly increasing trends in haze days. Horizontal visibility, haze days, dry coefficient and API of three urban stations of Nanjing,Hangzhou,Hefei were analyzed, visibility was negative correlated with API in the haze days, and the correlation coefficients gradually increased in higher relative humidity.Aerosol scattering accounted for the most of extinction factors,and Bsa varied seasonally from the peak in winter to the bottom in summer.The highest probability of haze occurred between150μg·m-3and200μg·m-3in the concentration of PM2.5.The correlation of visibility,relative humidity and concentration of PM2.sare analysised.The threshold aerosol concentration that is corresponding to the low visibility (<10km))is47μg·m-3.When aerosol concentrantion are very high(>200μg·m-3) the change in visibility is not sensitive to aerosol concentration.Nanjing suffered heavy haze in December2013.The surface was controlled by weak high-pressure and uniform pressure,small wind speed,great air relative humidity and the inversion led to the pollutant accumulated on the surface layer for long time,hard to diffusion. The concentration of SO42-,NH4+and NO3-accounted for87%.The PCA models identified four sources of PM2.5:secondary sources(coal or motor vehicle exhaust), road dust,fuel combustion(incineration),the contribution rate was54.609%,17.709%,11.993%, respectively.