Variation Characteristics And Source Apportionment Of Water Soluble Inorganic Ions In Atmospheric PM_2.5 In Xi’an

Environmental issues related to human health and survival,has been a hot issue of concern and scientific research.In recent years,Xi’an has repeatedly appeared heavy pollution haze,not only a serious impact on the traffic,environmental problems are more threatening people’s physical and mental health.The air environment in Xi’an city is to fine particulate matter(PM_2.5)pollution,with two nitrogen oxides and photo-chemistry pollution,and pollutant source complex,affecting a wide range,long duration and other characteristics.This study from June 2014 to March 2017 during the Xi’an PM_2.5 and PM_2.5 water soluble inorganic ion concentration data and related meteorological data,research and analysis of the main city of Xi’an PM_2.5 water soluble inorganic ions change characteristics.The effect of relative humidity on the change of water soluble inorganic ions in PM_2.5 was studied.At the same time,the source apportionment of water soluble inorganic ions in PM_2.5 was studied by means of the correlation coefficient matrix,enrichment factor method and the contribution ratio of different sources.The results show that:In Xi’an NO₃¹,NH₄⁺,SO₄^2-,Cl^- four kinds of main ions mean annual total ion of PM_2.5 are 91.84%,there is a significant change in the trend,the peak appears in December or so.Na⁺,Ca²⁺,Mg²⁺,K⁺four kinds of ion concentration change trend is stable,in the ±1 g/m³ concentration range fluctuations.According to the concentration value of NO₃¹and its diurnal variation,the mobile source has the largest contribution to NO₃¹in PM_2.5 in the main urban area of Xi’an.In winter,spring haze is more serious in 2016,the most serious haze in the study period,the proportion of the total number of days of fog and haze in the month of 83.87%,in February 2015 the second time inJanuary.In a complete haze cycle of SO₄^2-,NO₃¹,NH₄⁺,Cl^- four ions increased significantly.SO₄^2- accounted for the largest proportion of the haze reached 42.3%.While NO₃¹accounted for only 27.5% of the largest proportion of these two ions accounted for almost PM_2.5 of water-soluble inorganic ions of 70%.The effects of rainfall and relative humidity on NO₃¹,SO₄^2- and NH₄⁺ were significant,while the effects on Cl^-,Na⁺,K⁺,Ca²⁺and Mg²⁺were almost negligible.The contents of NO₃¹,SO₄^2-and NH₄⁺ in PM_2.5 were increased when the relative humidity increased and the relative humidity was maintained above 90% in the case of rainfall erosion in the process of rainfall.And the relative humidity began to decline,NO₃¹,SO₄^2-,NH₄⁺ content is also followed by the decline.The change in relative humidity affects the change in the composition of a single PM_2.5 particle.The proportion of NO₃¹,SO₄^2-,NH₄⁺in PM_2.5 and PM_2.5 was increased in the absence of rainfall scouring.When the rainfall is large,the scouring effect of rainfall begins to decrease the proportion of NO₃¹,SO₄^2-,NH₄⁺ and these three water-soluble ions in PM_2.5 and PM_2.5.In the process of rainfall due to rainfall and other meteorological factors coupled with the impact of human factors make the situation more complicated.In the whole rainfall process,the relative humidity does not reach 90%.When the relative humidity decreases after the rainfall,the NO₃¹,SO₄^2-and NH₄⁺contents in PM_2.5 do not necessarily follow the decrease,but the humidity is sometimes absorbed by the humidity The role of its content will continue to increase.The correlation matrix shows that the correlation coefficient of PM_2.5 SO₄^2-and NO₃¹,NH₄⁺ and Cl^-,NH₄⁺ and K⁺,Ca²⁺ and K⁺ are more than 0.50,that between ions have similar sources or ways of forming.The neutralization effect of ammonia in Xi’an PM_2.5 is higher than that of calcium and magnesium.The inorganic ions dissolved in Xi’an PM_2.5 water source analysis showed that SO₄^2-,NO₃¹,NH₄⁺ and Cl^- in Xi’an most mainly from Artificial pollution pollution;Na⁺ and Cl^- are mostly derived from the crust.In general,the water soluble inorganic ions in Xi’an PM_2.5 were mainly affected by Artificial pollution pollution sources,the contribution to the total ion concentration was 89.94%.