Characteristics Of Water-soluble Inorganic Ions In PM_2.5 Using Online Monitoring Instruments In Zhengzhou

With the acceleration of urbanization,the problem of air pollution becomes more and more serious.To understand the pollution characteristics of water-soluble inorganic ions in PM_2.5 in Zhengzhou,this study started from December 2017 to November 2018by using an on-line gas composition and aerosol ion monitoring system?AIM,URG-9000D?for observation the water-soluble inorganic ions in PM_2.5 in Zhengzhou continuously.The characteristics and sources of the mass concentration of water-soluble inorganic ions in PM_2.5 in Zhengzhou were analyzed.In addition,the characteristics of water-soluble inorganic ions combined with meteorological factors and concentration of gas pollutants were also analyzed.This study found that the water-soluble inorganic ions in PM_2.5 in Zhengzhou were seriously polluted,and the mass concentration was relatively high,accounting for about52.1%in PM_2.5.Secondary inorganic ions include sulfate,nitrate,and ammonium?SNA?,were the most important water-soluble inorganic ions,accounting for 82.7%of the total water-soluble inorganic ions?TWSIIs?.The mass concentration of water-soluble inorganic ions in PM_2.5 in Zhengzhou is the highest in winter,followed by autumn and spring,and the lowest in summer.The diurnal variation characteristics of the total water-soluble inorganic ion mass concentration in different seasons were different.The diurnal variation characteristics of the TWSIIs mass concentration in the whole year,spring,summer and autumn were both single-peak distribution,with the peak value around 09:00,while the pollutant mass concentration in winter was higher,but there was no obvious diurnal variation characteristics.By comparing the correlation between on-line monitoring results and traditional membrane sampling analysis results,it was found that for Cl^-,NO₃^-,SO₄^2-and NH₄⁺,the two methods had a good correlation.Meteorological conditions had a significant impact on water-soluble ion mass concentration.When the wind speed was relatively high,it could remove pollutants.When the wind speed was relatively low,it was greatly affected by local and surrounding area transmission.The water-soluble inorganic ions were negatively correlated with temperature,especially with semi-volatile ions such as Cl^-,NO₃^-and NH₄⁺.And the water-soluble inorganic ions were positively correlated with relative humidity,especially with secondary inorganic ions.The sulfur oxidation rate?SOR?in Zhengzhou was the highest in summer,followed by spring and autumn,and the lowest in winter.The nitrogen oxidation rate?NOR?was the highest in winter,followed by autumn and spring,and the lowest in summer.Both the values of SOR and NOR increase with the increase of pollution,and the influence of relative humidity on SOR is greater than that of NOR,while the influence of temperature is greater than that of SOR.The water-soluble inorganic ions in PM_2.5 in Zhengzhou were mainly affected by secondary conversion sources,fossil fuels and coal burning sources,soil dust and construction dust sources throughout the year and in each season,and secondary conversion sources were the main contribution sources.The water-soluble inorganic ions in PM_2.5 in Zhengzhou were affected by local pollutant discharge and surrounding area transmission in four seasons,especially in summer.