The Preliminary Study Of The Characteristics Of Aerosols During Haze And Its Effect On Visibility In Guangzhou

Guangzhou is the political, economic and cultural centre of Guangdong Province with an area of 7475 square kilometres and a population of 11.05 millions. With the rapid development of economy over the past 25 years, Guangzhou has experienced hazy conditions that range from slight transient haze episodes to severe haze episodes. The rapid increase in fossil fuel usage led to an increase in aerosol concentrations and a decrease in visibility in this region. Visibility degradation has become one of the major problems of public concern in Guangzhou city. As a new meteorological problem and environmental catastrophic phenomenon, haze frequently occurred in the Pearl River Delta. In order to characterize the features of haze and to understand haze formation mechamism, it's very necessary to investigate the physical and chemical characteristics of aerosols during haze.In this study, PM10 characteristics and its effect on visibility during haze in Guangzhou city were investigated. First of all, both the long term and short term variation trends of atmospheric visibility were interpreted by analyzing the past data of prevailing visibility. Second, the correlation of atmospheric visibility with its major meteorological and pollutant parameters was established. Finally, the relationship between visibility degration and chemical species was derived by using multiple linear regression techniques.Regular visibility was observed during the period of 2002-2006. The observed visibility was mainly in the range of 2-6km. The visibility below 6km was about 62% of total observation days and poor visibility was usually occurred in autumn and winter. RH and wind speed were the most important meterological factors to influence the air visibility. In this study, the air particle pollution during haze was very serious and much higher than that in normal days. Accumulation mode aerosol, which is generally thought to dominate light scattering due to their high scattering efficiency, was consistent with coarse mode aerosols in normal days and higher than coarse mode aerosols in haze days. Three haze modes: summer forenoon mode, winter fluctuation mode and winter stabilization mode were summarized according to the variation of air visibility. Summer forenoon haze last only for several hours and winter fluctuation mode and winter stabilization mode always last for long time and deserved heavy pollution.PAHs and BEQ (BaP-equivalent) values (12.95) in winter haze were much higher than in other periods. Furthermore, relative higher value of IcdP/(BghiP+IcdP) and low value of Cmax, CPI, and BghiP/BeP in winter haze could be attributed to the growth of motor vehicle usage and energy consumption in winter.During the sampling period(2002/6/30-2003/07/01), secondary pollutants (SO₄^2-,NO₃^-and NH₄⁺) were the major chemical components in haze days and their concentrations show a rapid increase from normal to haze days, while primary pollutants (Na⁺, K⁺, Ca²⁺ and Mg²⁺), accounting for a small fraction of water-soluble organic compounds, are relatively stable. Sulfate was the largest single compound and nitrate experienced the largest variations in water-soluble inorganic ions.The proportions of SOC (secondary organic carbon) in haze days were much higher than those in normal days. The proportions of SOC in winter haze, summer haze, winter normal and summer normal were about 65%, 56%, 14.2% and 34%, respectively.The abundances of PM10, OC, EC, n-alkanes, PAHs, sulfate, nitrate and ammonia in haze days were 3.7, 4.3, 2.3, 3.0, 3.5, 3.7, 9.7 and 3.2 times normal days, respectively. Higher concentrations could be due to more stable boundary layer in haze days. Finally, multiple regression technique applied in chemical composition and visibility showed that carbonaceous and nitrate in haze days and TC and sulfate in normal days were likely the major contributors to visibility degradation.