Haze Phenomenon And Analysis Of The Characeristics Of Its Pollutants In Nanjing Area

The climatic characteristics and causes of hazy phenomena in Nanjing were analyzed based on surface observations obtained from Nanjing Meteorological Station and five suburban stations (Jiangpu, Liuhe, Lishui, Jiangning and Gaochun) from 1961 to 2006. The frequency of occurrence of hazy phenomena had the following trend: winter > spring > autumn > summer. The annual occurrence of hazy days had been increasing during the last forty-six years, and that a negative correlation exists between visibility and relative humidity during hazy periods. Meteorological factors have a significant effect on the occurrence of hazy phenomena. For example, hazy phenomena often occur when the wind speed was small and the relative humidity was high. The increasing trend of hazy days might be resulted from the increasing number concentration of total suspended particles (TSP) in the atmosphere, especially the fine-mode particles. The annual tendency, monthly and seasonal distribution of main air pollutants SO₂, NO₂ and PM₁₀ and the quality of the atmosphere in Nanjing have been analyzed based on the atmospheric monitoring data from 2002 to 2006. The results show that, during the last five years, there have been a considerable increase in SO₂, a remarkable decrease in PM10, and a slight increase in NO₂ concentrations. PM₁₀ was the dominant pollutants while the concentration of SO₂ and NO₂ were relatively low. All of the three pollutants presented minimum concentrations in summer. A comparison of the concentrations of the three pollutants under different meteorological conditions has revealed that a negative correlation existed between the concentrations of pollutants and wind speed and the maximum concentrations of pollutants were generally observed when the wind was blowing from the southeast. Precipitation had an important cleanup effect on pollutants, while a worse situation occured during haze or fog days. A negative correlation also existed between the visibility and the concentrations of PM₁₀ or NO₂. The air pollutants showed a "Weekend Effect" that their concentrations were obviously low during the weekends.Two sampling position were set up to investigate the characteristics of fine particles in Nanjing. One was in Nanjing University (representing the urban area). The other one was on the campus of Nanjing University of Information Science and Technology (representing the suburb region). The sampling was operated for 5 days in each season in 2007 to perform aerosol sampling. The mass concentration, water-soluble ion and elemental composition of fine particles were detected by weighing method, ion chromatograph, inductively-coupled plasma chromatograph separately. The results showed that water soluble anions were important components of PM_2.1 whose weight percents were 46.99% (urban) and 42.32% (suburb). The concentration of all the anions in PM2.1 was the minimum in winter. A high correlation lay between NH₄⁺ and SO₄^2-, which meant that they might exist in the form of (NH₄)₂SO₄. The SOR (conversion ratio of SO₂) and NOR (conversion ratio of NO_x) were determined largely by temperature: SOR increased and NOR decreased markedly when the temperature was high. Due to the NO₃^-/SO₄^2- mass ratio<1, stationary source such as coal burning were the major sources of SO₂ and NO_x. The mass concentration and enrichment factor of elements suggested that Pb, As, Zn, Hg, Cu, Cr and Ni were anthropogenic pollutants. Their pollution was much heavier in the urban than that in the suburb area. The water soluble ions SO₄^2-, NH₄ and the elements Pb, Zn had superiority in PM_21., while F^-, Cl^-, NO₂^-, NO₃^- and Ca, Mg, Na were enriched in coarse mode particles.