Study On Migration And Transformation Characteristics Of Wet Deposition Nitrogen Pollutants In Xi’an

In this paper,14 precipitation events（13 rainfall events and 1 snowfall event）in Xi’an city during the one-year period were selected,and multi-phase nitrogen pollutants were taken as the research object to master the wet settlement and roof runoff load pollution conditions based on time series（early and later stages of rainfall）.The interphase migration and transformation of nitrogen pollutants and the contribution of each phase pollution load in the course of rainfall and roof runoff were deeply analyzed.The research results can effectively support the identification and control of wet settling nitrogen pollution.This paper draws the following main conclusions:（1）The analysis of 14 precipitation events shows that the p H and DO concentration of Xi’an are 6.65±0.18 and 8.79±0.26 mg/L in the process of wet deposition.The average concentrations of TN,NH₄⁺-N,NO₃^--N,NO₂^--N,COD and TON are 7.71±3.71 mg/L,4.53±1.69 mg/L,1.53±0.68 mg/L,0.08±0.05 mg/L,32.20±17.98 mg/L and 1.71±2.07mg/L.The seasonal difference of the concentration of pollutants in wet deposition was large.The average field concentration of pollutants was higher from March to June,and the concentration was lower from August to November.（2）The p H and DO concentration of Xi’an roof runoff were 6.74±0.16 and9.07±0.31 mg/L respectively.The average concentration values of TN,NH₄⁺-N,NO₃^--N,NO₂^--N,COD and TON are 11.84±5.42mg/L,6.22±2.62mg/L,2.78±1.57mg/L,0.18±0.08mg/L,70.12±17.38mg/L and 2.64±2.77mg/L.Except COD and NO₂^--N,the variation trend of the concentration of other pollutants shows that the concentration is higher in winter,followed by spring and autumn,and the concentration is lower in summer.Compared with roof rainfall runoff,roof snowmelt runoff has better water quality.（3）The load equivalents of pollutants at the initial stage of different rainfall were significantly different.All nitrogen pollutants in rainfall showed obvious scour reduction effect under the scour effect of rainfall and runoff,and the scour characteristics of nitrogen pollutants in each form were similar over time series in the wet deposition process and runoff process.In different rainfall sessions,the correlations between the concentrations of pollutants in wet settlement and roof runoff,and between the concentrations of pollutants and rainfall intensity were different.（4）NH₄⁺-N was the main form of dissolved nitrogen in wet deposition and roof runoff in different rainfall events.The atmospheric wet sedimentation process contributes77%of TN,78%of NH₄⁺-N,64%of NO₃^--N,60%of TON,and 46.7%of NO₂^--N in roof runoff.Under different rainfall events,the contribution ratio of wet sedimentation to NO₂^--N and TON in roof runoff was significantly different...