Variation Characteristics Of PM_2.5?PM₁₀ Concentration In The Beibei Area Of Chongqing And Their Relationship With Precipitation Acidity

With the rapid development of China social economy,most of provinces appear haze seriously.Chongqing is known for the City of Fog.,as the old industrial base of the southwest area.Because of the special basin terrain,the high frequency of static-wind appears in Chongqing.What`s more,the atmospheric particulate matter is not easy to spread,lead to the air quality is bad,and the acid rain frequency is high as a result.Meanwhile,Chongqing air quality is directly related to the health of residents and the development of social economy as the economic center of Southwest China.Several researches indicate that the main causes of haze are closely related to PM_2.5 and PM₁₀,which also have an effect on the acidity of precipitation.Therefore,it is of great significance for controlling and improves the air pollution in Chongqing to discuss the relationship between the change of atmospheric particulate matter and the acidity of precipitation under different weather conditions in Chongqing.This paper takes the top floor of School of Geographical Sciences as an observation point,which belongs to Southwestern University located in Beibei district of Chongqing City.118 qualified samples of PM_2.5?PM₁₀ from May 2015 to April 2016 were collected and analyzed.In addition,38 precipitation samples from June 2015 to September 2015 were collected to study the relationship between the concentration of acid ion and atmospheric particles.We also tested the pH and electrical conductivity?EC?of precipitation,as well as the concentration of SO₄^2-and NO₃^-.The results are as below:?1?Time variation characteristics of atmospheric particulate: the concentration range of PM_2.5 and PM₁₀ is very large during observation.The data were recorded as 34.4⁷1?g/m3 and 54.2⁹0.2?g/m3 separately.On the other hand,the variation trend of atmospheric particulate concentration is basically the same,the peak appears in winter,and the change range was relatively stable;while the bottom appears in summer,and the change was larger.In other words,air quality was best in summer,followed by autumn and spring,and winter was the worst.This may be resulted by the special topography and climate in Chongqing: it is humid in winter with small wind,which usually causes fog,exacerbating the pollution of atmospheric particulates;while in summer,the precipitation is adequate to clean the particulate,which can reduce the degree of pollution.The correlation coefficient between the concentration of PM_2.5 and PM₁₀ was R=0.93,and the ratio of PM_2.5 and PM₁₀ was up to 0.55⁰.79,that draw the conclusion that the effect of PM_2.5 to air quality was larger than PM₁₀.?2?The relationship between atmospheric particles and meteorological factors: with the statistics of SPSS,the results indicated that the correlation coefficient of PM_2.5,PM₁₀ and precipitation are-0.77 and-0.78,and the average wind speed was-0.67 and-0.58 respectively.The precipitation and wind speed was working on cleaning and diluting the particles;meanwhile,the correlation coefficient between the average air pressure and particles of PM_2.5 and PM₁₀ is 0.79 and 0.66 respectively;in high humidity condition,there is correlation between the humidity and atmospheric particulate.In addition,the test samples of atmospheric anion,NO₃^-/SO₄^2-average of 0.37,infer that the main sources of Chongqing for stationary sources,this may be associated with the energy structure of Chongqing is given priority to with coal.?3?The relationship between precipitation and PM_2.5?PM₁₀: 28.9% of the precipitation in Beibei district of Chongqing is acid rain in summer,which usually has low pH,as a result,the air pollution in the summer of Beibei district was lighter.The EC of precipitation is low,and the correlation coefficient between EC and pH is R=0.23,which indicates that the correlation between them is poor.The main acid ions in summer precipitation are SO₄^2-,and the change trend of SO₄^2-in atmospheric particulate is similar to that in precipitation,which indicates that the atmospheric particulate has a direct impact on precipitation acidity.The reason may be that the content of SO₄^2-in the atmospheric particles is higher,which is more likely to blend in the precipitation,which leads to the decrease of pH value and the acid rain.However,the contribution of NO₃^-to the acidity of precipitation is increasing year by year,moreover the ratio of SO₄^2-/ NO₃^-is decreasing,Which indicates that the energy structure is transforming from coal to a mix of coal and petrol.