| In order to build the “World Ecological Garden City”, Chengdu government hasissued a series of effective measures, due to which the air quality of Chengdu hasbeen improved to some extent. According to the Chengdu Environment QualityBulletin from2006to2010, the air quality is gradually becoming better than before,but the acid rain problem remains seriously, especiallyin the eastern part of Chengdu.Tracking the right sources of acid material in precipitation has become the key factorsto improve the quality of atmospheric environment. Stable isotope analysis is areliable method to track acid rain precursors, such as sulfur dioxide, ammonium, andnitrogen oxides.This paper has collected38samples of precipitationinChengdu eastern areasfrom May2011to October2011. By systematically analyzing the characteristics ofmajor inorganic ions, sulfurisotope, nitrogen isotope’s influencing factors andcharacteristic values, the paper has revealed the sources of sulfur, nitrogen in theprecipitation, which canprovide a theoretical basis for the prevention and controllingof air pollution in Chengdu.The results indicate that:(1) The order of the weighted average equivalent concentration of anion inprecipitation is: Sulfate ions> nitrate ions> chloride ion> fluoride ion. Sulfateaccounts for69.18%of the total inorganic anion. Nitrate inorganic anions contribute17.69%to the total value. The main acid rain type is sulfuric acid, and the nitrateconcentration gradually increased. It has a trend that the type of acid rain is changinginto the combination of the sulfuric acid with nitric acid. The order of the weightedaverage equivalent concentration of cation in precipitation is: ammonium calcium> potassium>sodium> magnesium ion.Ammonium inorganic cation is59.14%of thetotal contribution, and the contribution of precipitation for ammonium nitrogenincrease larger. The pH range of the precipitation is3.12~6.27, with the average of3.59, accounted for92.1%of the proportion. The acidity of the precipitation of thestudy areaand its acidification frequency is very high, while compared to the past, thefrequency of acid rain decreased.(2) The sulfur isotope values range of the precipitation is-1.5‰～+6.6‰，with the average of+2.6‰. The monthly average of the sulfur isotope is positive inprecipitation samples. The order of the isotopic values is: August> October> June>September> July> May. The sulfur isotope values have obvious monthly variation,which may due to the different wind direction in different seasons, since temperature、the influence of rainfall、pH and sulfate concentration changes is quite slight. Theammonium nitrogen isotope values range of the precipitation is-27.3‰～-11.0‰，with the average of-21.8‰. The monthly average of the ammonium nitrogenisotope is negative. The order of the isotopic values is: August> July> May> June>October> September. The sulfur isotope values have obvious monthly variation, too.Temperature is a factor affecting ammonium nitrogen isotope values, while the effectof wind direction、rainfall frequency、pH and ammonium concentration changes isslight. The nitrate isotope values range of the precipitation is-9.8‰～-0.2‰, with theaverage of-5.2‰. The monthly average of the isotopes of nitrate is negative, the orderof the isotopic values is: May> August> September> October> July> June, the nitrateisotope valueshave obvious monthly variation, too. The effect of wind direction、temperature、rainfall frequency、pH and ammonium concentration changes is slight.(3) The source of sulfur in atmospheric precipitation in the study area comesfrom the sulfur emissions, coal and oil combustion of the sulfur, chemistry of sulfurand sulfur-containing fuel-burning smelter. The main reason of sulfur increasing inatmospheric precipitation in the study area is vehicle exhaust emissions, while thecontribution of coal burning is less. Considering that industrial and energy structureis playing an active role in protecting the quality of atmospheric environment inChengdu, sea spay contribute sulfur only in the summer. The main reason ofammonium nitrogen increasing in atmospheric precipitation in the study area ishuman and animal excreta. The source of agricultural soil releasing is seasonal. Thesame with sulfur source, vehicle exhaust emissions of nitrogen oxides is the mainsource, and the release of agricultural soils and biological processes is anotherreason for the increasing of nitrate in atmospheric precipitation in the study area, while the lightning process only contribute to the increase of nitrate in the summerthunderstorms.(4) In precipitation samples, the correlation of ammonium, nitrate and sulfate isclose, the same with potassium ions, sodium ions, calcium ions and magnesium ions,which means that they may have the same sources. The inorganic ions in theprecipitation remains in the form of calcium nitrate, magnesium nitrate, potassiumnitrate, potassium sulfate, ammonium nitrate and ammonium sulphate. The ratio ofsulfate/nitrate is3.03.Compared to2011, the ratio is less increased. Sulfate inprecipitation are the main acid factors. The hydrolysis process of the acid saltprecipitation contribute to the pH value of precipitation. The ratio of sulfate/(nitrate+chlorine ion) is2.60, which indicates that the nitrate has a tendency ofincreasing the acidic contribution of precipitation. |
PDF Full Text Request