The Chemical Characteristics And Nitrate Sources Analysis Of Precipitation In Typical Cities In Southeast China

In recent years,with the acceleration of urbanization,the outbreak of population and the increase of motor vehicle in the whole world,the concentration of pollutants in the atmosphere is gradually increasing,which not only has a greater impact on the water environment,but also endangers the stability of the ecosystem.Therefore,the analysis of the composition and sources of pollutants in atmospheric precipitation is helpful to monitor the air pollution in cities and provide scientific basis for the prevention and control of air pollution in Hangzhou and Huzhou.Through the research,the main conclusions are as follows:（1）During the sampling period,the total value of δ¹⁸O in Hangzhou and Huzhou ranged from-14.87‰^-1.64‰,with an average of -7.10‰;and the value of δ²H ranged from-109.70‰¹.16‰,with an average of -36.42‰.The Local Meteoric Water Line（LMWL）was explained with the equation:δ²H=8.87δ¹⁸O+25.95.The slope and intercept are higher than those of the global atmospheric precipitation line（GMWL）and the local atmospheric precipitation line in China（CLMWL）,which are related to the geographical location of Hangzhou and Huzhou.In addition,the slope and intercept of Huzhou LMWL are larger than those of Hangzhou due to the heavy rainfall.The seasonal variations of the values of δ¹⁸O and δ²H values in atmospheric precipitation in Hangzhou and Huzhou are the largest in spring,lowest in summer,which is related to regional geographical factors and the sources of different air masses.（2）The D-excess values ranged from 4.42‰⁴0.25‰,and the average value is 20.39‰ in Hangzhou and Huzhou.The D-excess values for the winter,spring and autumn are much higher than those in summer,which is also related to the different sources of air masses.The relationship between theδ¹⁸O value and the temperature in precipitation is as follows:δ¹⁸O=-0.12T-4.77.There is a weak negative correlation between the δ¹⁸O value and temperature.The monsoon climate suppresses and masks the temperature effect to a certain extent,thus showing an anti-temperature effect.The relationship between δ¹⁸O and rainfall is:δ¹⁸O=-0.0036P-6.34,showing an obvious rainfall effect.（3）The pH in Hangzhou and Huzhou is lowest in winter and highest in summer,which is due to the high concentration of SO₂ and NO₂ in the atmosphere in winter.The order of concentration of cations and anions in precipitation in the whole region is:Ca²⁺>HCO₃^->SO₄^2->NH₄⁺>NO₃^->Cl^->Na⁺>Mg²⁺>K⁺.The ion concentration value is the highest in winter and the lowest in summer,rainfall is the key factor affecting seasonal variation.The SO₄^2-/NO₃^-value of the atmospheric precipitation in Huzhou City is 1.89,and the SO₄^2-/NO₃^- value in Hangzhou is 1.38,showing that the type of precipitation pollution in Hangzhou has gradually changed from sulfuric acid type to mixed type.Ca²⁺,Mg²⁺and K⁺showed a good correlation,because the EF_marinearine values of K⁺and Ca²⁺ were much greater than 1,indicating that they mainly came from soil.There is also a significant correlation between Cl^- and Na⁺,indicating that they have a common marine source.In addition,88% of NO₃^-and 99% of SO₄^2-are mainly from anthropogenic sources such as coal combustion.（4）The average concentration of NO₃^--N,NH₄⁺-N and DTN in Hangzhou was 0.63 mg N L^-1,0.94 mg N L^-11 and 1.64 mg N L^-1,respectively.The average concentration of NO₃^--N,NH₄⁺-N and DTN in Huzhou is 0.58 mg N L^-1,0.70 mg N L^-11 and 1.37 mg N L^-1,respectively.The concentrations of DTN,NH₄⁺-N and NO₃^--N have obvious seasonal variations,which may be related to the comprehensive effects of precipitation,pollutant emissions,oxidation conditions and exogenous inputs in Hangzhou and Huzhou.The range of the value of δ¹⁵N_-NO3NO3 and δ¹⁸O_-NO3NO3 in Hang zhou is-2.35‰³.72‰,52.86‰⁸6.50‰,respectively;and the value of δ¹⁵N_-NO3NO3 and δ¹⁸O_-NO3NO3 value in Hang zhou is-1.86‰².94‰,43.80‰⁸0.96‰,respectively.Nitrate in the atmosphere of the study area mainly comes from vehicle exhaust emissions,agricultural soil release,coal and biomass combustion.The values??ofδ¹⁵N_-NO3NO3 and δ¹⁸O_-NO3NO3 are lower in summer and spring,and higher in autumn and winter,which is related to the influence of different nitrate sources and atmospheric chemical processes.