Characteristics Of Haze And Observational Study On Physical Properties Of Aerosols In Hangzhou

Based on ground and upper-air meteorological data during1998-2010and aerosols data in2011from the national reference climate station of Hangzhou, this paper studied climatic characteristics and the influence of weather conditions on haze and the variation of aerosols and its influence factors. The physical properties of aerosols in haze and non-haze weather were compared. Furthermore, the typical haze weather process and properties of aerosols were analyzed. The main conclusions are shown as follows:(1) The average number of haze days was162.8per year. The annual variation of haze days were mainly related to the aerosol pollution conditions and changes of surrounding environment. The largest occurrence frequency of haze days happened in December, and the least happened in July. The main reason was that strong air convection and adequate rainfall appeared in summer, which is conducive to the dispersion of pollutant. By contrast, atmospheric stratification is stable and inversion layer is much thicker in winter, so pollutants were much easier to gather together. Therefore, the haze days in Hangzhou have high-occurrence frequency in winter and low-occurrence frequency in summer. High-pressure is the main synoptic situation in which haze occurred, while in the weather system of cyclone and easterly belt, haze days occurred rarely. The haze days always occurred in neutral stratification. The occurrence frequency of haze day was52%in cloudy days. Calm is the optimal condition of haze occurring. The averaged inversion strength at20:00is much higher than that at08:00, which is the opposite of inversion thickness under the haze. Inversion is an important factor to haze.(2) The seasonal variations of PM2.5, PM10, black carbon and scattering coefficient were decided by atmospheric circulation and the changes of meteorological conditions. The diurnal variations associated with boundary layer evolution, traffic emissions and human activities. The background values of black carbon and scattering coefficient were3.01μg/m3and238.9Mm-1, which were calculated by fitting hour frequency distribution. Precipitation more than10mm can effectively clear20%～50%black carbon in atmosphere. The wind speed played a distinct role in diffusing and conveying to aerosols. Scattering coefficients interval difference in different wind direction had no obvious difference because of special geographical position. The mass concentration of PM2.5, PM10, black carbon and scattering coefficient in haze was higher than in non-haze. With the increasing of haze level, these observed values became larger and larger.(3) In haze process of June,2012, the main reasons, which caused poor visibility and extremely serious pollution, were the combined effects of long-distance transmission of pollutants, local pollution emission and static stability of weather. The high value of aerosol single scattering albedo is0.92-0.96which indicated that the aerosol had stronger ability for light scattering in haze weather. The values of Angstrom exponent were0.21and0.92in fog weather and dry haze weather, respectively, which indicated the distribution of aerosol particle sizes had significant differences.