| Current research on haze, which is a hot issue of environmental problems, has been focused on the analysis of weather and climatic characteristics, meteorological cause and chemical composition. The study on the aerosol vertical distribution of haze has still rarely been reported. In this study some new meaningful information for operation of warning and forecasting of haze at Shanghai was revealed.Using the observational data from the ground-based Micro-Pulse Lidar (MPL) and Sun-photometry at Shanghai Urban Environment Meteorology Center from March 2009 to February 2010, the aerosol extinction coefficient and opticle depth were retrieved according toWelton method. The trend of the parameters was consistent with the ideal profile of numerical simulation. In spite of this, there were some errors in the low atmosphere and moving average could minimize the influence of remote signal noise. The results showed that the variation tendencies of inversion and observation of aerosol optical depth (AOD) were almost the same; Because AOD observed by sun-photometry was for the entire atmospheric column and that of lidar inversion was only for the atmosphere near surface,80% of the inversion values were lower than the observations. Due to the large fluctuations of inversion values, the retrieval process needs to be further improved.With the data from Milos500-Finland Vaisala Company's seven elements automatically observational weather station and the newly issued standard for meteorologically observational operation, days of haze and haze-free, dry and damp haze and haze of different intensity were statistically analyzed. The results revealed that the number of haze days varied ranging from the largest to the fewest in winter, summer, spring and autumn sequently. Dry haze days, which occurred most in winter, appeared more frequently than damp haze days, which occurred most in summer. For haze of different intensity, slight haze occurred most in spring and summer, while severe haze in winter. Diurnal and seasonal variation of the aerosol extinction coefficient and the distribution of AOD for different heights in troposphere were analyzed, using the data retrieved by Micro-Pulse Lidar at Shanghai Urban Environment Meteorology Center from March 2009 to February 2010. The results indicated that AOD below lkm accounts for 64% of that betweem 0-6km when haze occurred at Shanghai and 44% during haze-free periods. The AOD values are greater than 0.04 during haze periods and less than 0.04 during haze-free periods. This shows that increasing aerosols at low atmosphere is the main cause of haze. The vertical gradient change in seasonally average extinction coefficient for haze was significant, ranging from the largest to the fewest in winter, summer, spring and autumn sequently. During damp haze (80%<RH<95%) periods the fluctuations of extinction coefficient, changing from 0.0001 to lkm-1, are larger than that during dry haze(RH<80%) periods, which fluctuated around 0.1km-1. Below 500m, the phenomenon that extinction coefficient of damp haze is larger than that of dry haze is most obvious in winter, so damp haze has a greater contribution to reduced visibility than dry haze.The boundary-layer height, particle concentration, relative humidity and wind speed and direction, which are the main factors affecting the occurrence of haze, were also studied. The results showed that variation of boundary-layer height for four seasons were similar, with the highest height 725～825m. Surface aerosol mass concentrations during the haze periods were ranging from 30 to 60μg/m3 for PM1,and 45 to 75μg/m3 for PM2.5, and during the haze-free periods they were from 10 to 25μg/m3 and 15 to 35μg/m3 respectively. Severe haze easily occurred in the winter due to the lowest atmospheric boundary-layer height and the highest concentration of particulate matter; there were more damp haze and less severe haze in summer due to the lowest concentration of particulate matter and the maximum relative humidity. The surface wind was generally small over Shanghai during haze periods, at an average of 2.0m/s, referring to light wind condition, which leads to less atmospheric diffusion and haze occurrence.Finally, the typical haze case, including a slight,mild, moderate and severe haze, which occurred at Shanghai from 19 to 21, December 2008 was analyzed in this paper. Micro-Pulse Lidar, together with a variety of observational approaches, was applied in the analysis. The comprehensive analysis of aerosol optical properties and their vertical distributio before and after the haze can provides reference information for urban haze pollution control. |
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