Characteristics Of Atmospheric NH₃ Pollution And Its Impact On PM_2.5 In Urnban Area Of Jinhua

Ammonia（NH₃）is an important measure of alkaline gas in the atmosphere,and it is also the main body involved in the atmospheric nitrogen cycle.It will neutralize with acidic gaseous precursors to form secondary inorganic water-soluble ions,resulting in the pollution of atmospheric particulate matter PM_2.5.It is of great social significance to clarify the pollution characteristics of secondary water-soluble ions carried by NH₃ and PM_2.5,and to evaluate the influence of NH₃ on the formation of secondary water-soluble ions.In this study,the atmospheric particulate matter PM_2.5 and gaseous pollutant NH₃ were collected in Jinhua City,and the concentrations of the atmospheric NH₃and the ion components carried on PM_2.5 were measured.In addition,the meteorological conditions such as temperature and humidity were measured,the official report data of other gaseous pollutants were collected at the same time.This study mainly discussed the pollution characteristics of NH₃ and the pollution characteristics of secondary water-soluble ions carried on PM_2.5 in Jinhua City,and used correlation analysis to explore the relationship between NH₃ and other atmospheric pollutants in this area.Finally,the effect of NH₃ on the secondary inorganic components carried by PM_2.5 was evaluated.According to the analysis of the experimental results,the following main conclusions were drawn:（1）The variation range of atmospheric NH₃ pollution concentration in Jinhua City were0.02 ug/m³～13.8 ug/m³.The seasonal characteristics of atmospheric NH₃ concentration were significant,with the highest in summer,the second in spring,and the lowest in winter,which were mainly affected by temperature,agricultural activities and some other human factors.The daily variation of atmospheric NH₃ was obvious,and the concentration of atmospheric NH₃ was generally higher during the day than at night.Correlation analysis showed that NH₃had a certain relationship with atmospheric particulate matter,temperature and gaseous pollutants（SO₂,NO₂,CO）,and the influence of temperature was the most obvious.（2）The proportion of water-soluble ions（SNA）of SO₄^2-,NO₃^-and NH₄⁺carried on PM_2.5,about 41.0%,27.8%and 56.9%in winter and spring respectively.The proportion was relatively large,indicating that SNA was the main component of atmospheric particulate matter in Jinhua City in 2021.The concentrations of SO₄^2-,NO₃^-and NH₄⁺also had significant seasonal variation characteristics.The concentration of NH₄⁺and NO₃^-showed the order of winter>spring>summer;the concentration of SO₄^2-showed the order of summer>spring>winter.In addition,the SNA concentration had a certain characteristic of diurnal variation.Under the influence of sunlight and temperature,the concentration of NH₄⁺during the day was generally slightly lower than that at night,while the concentrations of SO₄^2-and NO₃^-during the day were higher than those at night.（3）The clustering of backward trajectory showed that the atmospheric diffusion and transmission in Jinhua City was mainly affected by the land wind in winter,and the atmospheric pollutants mainly came from southern Jiangsu,northern Zhejiang and the local area of Jinhua.Atmospheric diffusion and transmission in spring was affected by the combined action of sea breeze and land breeze,and air pollutants mainly came from the Yellow Sea,Ningbo,southern Jiangsu,northern Zhejiang and Jinhua in China.In summer,atmospheric diffusion and transmission were mainly affected by the sea breeze,and atmospheric pollutants mainly came from coastal areas such as the South China Sea and the East China Sea.（4）During the sampling period,atmospheric NH₃ was significantly correlated with the secondary water-soluble ions NH₄⁺,NO₃^-and SO₄^2-carried by PM_2.5.There was a good negative correlation between atmospheric NH₃ and fine-grained NH₄⁺concentration,which indicated that atmospheric NH₃ will be converted to NH₄⁺,and this process of atmospheric NH₃ gaseous transformation affected the atmospheric PM_2.5 concentration level.Atmospheric NH₃ and NO₃^-were significantly negatively correlated,which indicated that atmospheric NH₃ and NO₃^-were the relationship between reactants and products.NH₃ and HNO₃ in the atmosphere reacted to generate NH₄NO₃,which in turn affected the atmospheric PM_2.5 concentration level.Atmospheric NH₃ was significantly positively correlated with SO₄^2-,and exogenous sulfate had a greater impact on Jinhua’s atmospheric PM_2.5.（5）Temperature,relative humidity,wind speed and concentration of acid gaseous precursors（SO₂,NO₂）all had influence on the process of gaseous transformation of NH₃and NH₄⁺.The environment of low temperature and high humidity was conducive to promoting the conversion of gaseous NH₃ to particulate ammonium salts,resulting in an increase in the concentration of secondary aerosols.When the concentration of SO₂ and NO₂in the atmosphere was high,it promoted the formation of ammonium salts in the atmosphere,resulting in secondary aerosol pollution in the atmosphere.