The Characteristic Change Of Atmospheric Precipitation And Indicative Significance Of Dust Weather In Shiyang River Basin

The sand dust weather is mainly affected by the underlying surface and atmospheric motion.Desert and gobi in arid area and bare earth surface that the vegetation cover is very low can provide adequate dust sources for the occurrence of dust weather.Unstable air and air currents are the power source for the occurrence of dust weather.However,dust sources and power sources are two essential conditions for the occurrence of dust weather.Many scientists have carried out extensive research on the conditions of sand and dust weather including dust sources and power sources.Of course,it is also one of the main ways to understand and study the sand dust weather,so as to effectively control the dust weather.However,it is necessary to analyze and discuss the mechanism and main influence factors of sand dust weather in a more scientific way.Due to the unique significance of atmospheric precipitation in arid areas is the indication for dust weather.The concentration of the main anions and cations in the atmospheric precipitation also reflects the change of the chemical composition and the composition of the atmosphere in a certain extent.Atmospheric precipitation is one of the most effective ways to clean and purify the air pollution in the study area.With the occurrence of precipitation events and the cleaning and purification to atmospheric environment,a large number of pollutants that floating in the atmospheric environment into the precipitation.And this results in the change of the concentration of the main anion and cation in the precipitation.Finally,the p H,EC and the concentration of the main anion and cation in the atmospheric precipitation have also changed.As a result,the changes of p H,EC and ion concentration of atmospheric precipitation reflect the change of atmospheric environment to a certain extent.At present,the research on dust weather was mainly focused on the field of observation and analysis,cause and forecast,satellite remote sensing monitoring and geochemical tracing and other fields.The related research on dust weather indication of atmospheric precipitation chemistry only stays in research on the relationship between some climatic factors and the dust weather.There were few reports about the influence of the change of atmospheric precipitation on the sanddust weather.This paper analyzed and discussed the spatial difference of atmospheric precipitation,temporal variation and ion sources through analysis the p H of atmospheric precipitation,conductivity and the characteristics of main ions in the Shiyang River Basin.The results showed that:Through the analysis of precipitation samples in Shiyang River basin,the variation range of p H value of precipitation was from 6.62 to 8.53 in Shiyang River Basin,and the average value was 7.46 during the period of sampling.The precipitation in the Shiyang River Basin most concentrated in the p H value between 7and 7.5,followed by p H between 7.5 and 8.From the analysis of the changes in the different seasons,the order of p H value followed: spring?7.55?> winter?7.46?=summer?7.46?>autumn?7.36?,the p H value of spring was the highest.From the spatial scale change of p H value in the Shiyang River Basin,p H value showed an increasing trend from the upper reaches to the lower reaches?R2=0.8724?.The weighted average value of p H was 7.36 in upstream,and the midstream was 7.55,the downstream was 7.6.From the p H value of each observation site,the p H of Hesongyi,Minqin,Gulang,Wuwei,Xidahe,Jiutiaoling and Wushaoling was 7.63,7.6,7.52,7.51,7.36,7.36 and 7.36,respectively;The EC values in the Shiyang River Basin ranged from 17.28 to 787.00?s/cm,with a mean 186.66?s/cm.The maximum value appeared in February 28,2014,and the minimum value appeared in August 11,2013.The value of EC reached the peak in the winter and spring,but the EC value of summer and autumn is lower,especially summer's EC value.The EC value followed: winter> spring > autumn > summer,with the average values being 282.75?s/cm,238.76?s/cm,197.54?s/cm and144.81?s/cm,respectively.By analyzing the spatial variation in Shiyang River basin,the changes of EC was similar to p H that showed an increasing trend from upstream to downstream in the Shiyang River Basin.However,the increased trend of p H was significantly higher than EC?R2=0.3921?.From the each observation site of EC,Heisongyi?225.93?s/cm?was the highest and followed by Xidahe?218.58?s/cm?.The EC value of Wuwei,Gulang,Minqin,Jiutiaoling and Wushaoling was 176.06?s/cm,175.58?s/cm,155.98?s/cm,105.30?s/cm and 104.23?s/cm,respectively;The average ionic concentrations for SO₄^2-,Ca²⁺,NO₃^-,Cl^-,Na⁺,K⁺,Mg²⁺,NH₄⁺,NO₂^-and F^-were 28.74,17.77,12.16,8.24,5.71,3.83,3.42,1.97,0.44 and 0.19?eq/L.Among them,Ca²⁺and Na⁺ dominated cations and accounted for 71.80% of total cations composition,whiles SO₄^2-and NO₃^-dominated anions with a contribution of82.18%.The type of precipitation in study area was SO₄^2--Ca²⁺-NO₃^-,and three ions accounted for 71.14 % to the total ionic concentration.SO₄^2-,Ca²⁺ and NO₃^-accounted for 34.85 %,21.55 % and 14.75 % the total ionic concentration,respectively.The Jiutiaoling's sequence of Ca²⁺> Na⁺> K⁺> NH₄⁺> Mg²⁺ for cations is similar to Xidahe(Ca²⁺> Na⁺> K⁺> Mg²⁺> NH₄⁺).At the same,whether in Wushaoling or Jiutiaoling and Xidahe,the order of anions is SO₄^2->NO₃^->Cl^-.About cations in midstream,the order of Gulang has the same order as Heisongyi(Ca²⁺> Na⁺> Mg²⁺>K⁺> NH₄⁺).But about anions,Gulang is similar to Wuwei,and differ from Heisongyi.Minqin locates in downstream,the order was NO₃^->Ca²⁺>Cl^->SO₄^2->Na⁺>NH₄⁺>K⁺> Mg²⁺>NO₂^->F^-?p<0.05?for anions and cations,the concentration was 13.94,13.51,12.28,12.06,6.17,4.35,2.68,1.68,0.25 and 0.06?eq/L,respectively.The cations and anions concentrations showed great seasonal variation in the Shiyang River Basin.The order of the total precipitation ionic concentrations in the Shiyang River Basin was winter > spring > autumn>summer,with the mean values being 16.38,9.22,9.20 and 5.54?eq/L,respectively.The ion concentration of summer was the lowest and the concentration of winter and spring was higher.Through correlation analysis,factor analysis,enrichment factor analysis and endmember contribution analysis showed that the ions of atmospheric precipitation was mainly controlled by crustal and anthropogenic sources in Shiyang River Basin.Back trajectories suggested that the air mass arrived in Shiyang River Basin mainly from the dust sources region in Central or West Asia or Northwestern China through westerly circulation in dry season,while from the Indian Ocean or the Pacific Ocean through monsoon circulation in wet season.The precipitation can be divided into three types based on the vector of water vapor transportation: the monsoon precipitation,the westerly precipitation and the interaction precipitation.The frequency of monsoon precipitation accounted for 19% in all precipitation during thesampling period.The westerly precipitation accounted for 33% and the interaction precipitation was 48%.Through the analysis of the indication of p H,EC and ion concentration on the typical dust weather in Shiyang River Basin,p H and EC increased with the occurrence of dust weather.However,the indication of p H and EC on the sand dust weather was also affected by climatic factors,especially wind speed.With the occurrence of dust weather,the ions in precipitation showed an increasing trend in Shiyang River basin.From the overall change of the cation concentration with the typical dust weather occurred in Shiyang River basin,the change average values of Na⁺,K⁺,Mg²⁺,Ca²⁺ and NH₄⁺ was 22.62?eq/L,17.17?eq/L,9.83?eq/L,42.03?eq/L and-0.05?eq/L,respectively.The most sensitive cation was Ca²⁺,the next was Na⁺,K⁺ and Mg²⁺ were smaller,while NH₄⁺ was the least sensitive cation.The order of change values for anion concentration was SO₄^2-> NO₃^-> Cl^-> F^-> NO₂^-,and the change mean of anion was 40.92?eq/L,24.33?eq/L,21.10?eq/L,0.08?eq/Land0?eq/L,respectively.So The most sensitive anion was SO₄^2-,the next was NO₃^-,Clwas the same as NO₃^-,but NO₂^-wasn't change with the occurrence of dust weather.