Study On The Spatio-temporal Variation And Influencing Factors Of Atmospheric Precipitation Hydrochemistry In Lanzhou City

Precipitation can usually effectively remove aerosol particles and dissolved gaseous pollutants from the atmosphere,and is the most effective atmospheric purification mechanism for atmospheric particles.The chemical composition of precipitation is more and more prominently affected by human activities.In some places where human activities are intensive,human emissions even determine the chemical composition of precipitation.Lanzhou is affected by high energy emissions,special topography and meteorological factors,making Lanzhou air pollution more prominent in atmospheric particulate matter and SO₄^2-pollution.Therefore,the research on the water chemical composition of the atmospheric precipitation in Lanzhou is particularly urgent and has practical significance.This paper systematically collected long-term series of atmospheric precipitation samples from Lanzhou and background points,and measured the chemical components of atmospheric precipitation based on hydrochemical methods,and studied atmospheric precipitation at different time scales(within the year,seasons,and different time intervals of precipitation within the event).The temporal variation of chemistry and the regional differences in the chemical composition of atmospheric precipitation between urban and suburban areas;mainly used SO₄^2-to used mathematical methods to quantitatively calculated the contribution of anthropogenic sulfate;through the used of human activity factors,air pollution factors,meteorological factors(wind speed,Precipitation,temperature,relative humidity,etc.)and the ion contented in atmospheric precipitation,etc.,to discussed the current situation and caused of air pollution in Lanzhou.The results showed:(1)The Hydrochemical Composition and precipitation acid-base characteristics of different sampling points in Lanzhou city were different.The main ions in the study area were Ca²⁺ and SO₄^2- .High precipitation was accompanied by high annual wet deposition fluxes of various ions.The average pH values of different sampling points from large to small were Yongdeng>Yuzhong>Gaolan>Anning.Ca²⁺was the most important neutralizing compound in the precipitation of all sampling points,and the AP/NP(neutralization potential)values of the four sampling points were less than 1.Most of the AAI values of precipitation events were less than 100%,but the AAI index(ammonia availability index)of individual precipitation events was much greater than 100%.The concentration of ions in the precipitation in the study area was much higher than that in the southeast of China,but the acidity of precipitation was much lower than that in the southeast of China.Finally,the chemical composition concentration of water in the atmospheric precipitation of Lanzhou City in this study was compared with the previous research results in this area,and it was found that the ion concentration showed an upward trend.(2)From May 2019 to September 2020,the concentrations of major ions in precipitation at different sampling points in Lanzhou showed different trends with time,and the ion concentration fluctuated significantly.Specifically,the variation of chemical composition of precipitation with season was winter>spring>autumn>summer;The results showed that the concentrations of ions in the precipitation were higher in the dry season(October to next April)and lower in the wet season(May to September);The concentrations of most ion components in the precipitation collected in the same time interval keep a certain variation law.The whole variation process could be divided into three stages:initial high concentration stage,gentle stage and rebound stage.Based on the annual scale,the concentrations of ions in precipitation showed obvious spatial differences,and the distribution of ions in precipitation at different sampling points was inconsistent.(3)The enrichment factors of seawater and soil in different sampling sites were consistent,and most ions were enriched relative to the ocean and crust.In the study area,the contribution of chemical components of precipitation from sea and non sea sources was different,and the contribution of ions was also different.On the whole,the source of chemical components of atmospheric precipitation at each sampling point was mainly from human activities and crustal material input,while the input of marine components was very small.The contribution of man-made sulfate varied with regional distribution.According to the statistical analysis,all ion sources could be roughly divided into four categories,which were crust mixed source,industrial source,transportation source and agricultural source.In addition,correlation analysis was used to study the relationship between various chemical components in atmospheric precipitation and meteorological factors,atmospheric quality factors and human activity factors.Finally,based on the analysis of the source of the above ions,the corresponding atmospheric control countermeasures were put forward.