Chemical Composition And Source Analysis Of Atmospheric Particulate Matter In Lhasa During Rainy And Dry Season

Lhasa is an international tourist city with snowy plateau and ethnic characteristics.Due to its special geographical location,Lhasa has low atmospheric pressure,large temperature difference between day and night,and low ability to bear environmental pollution.Secondly,Lhasa has unclear four seasons and distinct rainy and dry seasons.Due to the great influence of rain erosion on particulate matter,this paper collected atmospheric PM_2.5,PM₁₀ and graded particulate matter samples manually in rainy and dry seasons from July to August and October to November in2021,analyzed and tested 10 water-soluble inorganic ions and 20 inorganic metal elements.The concentration,proportion and particle size distribution characteristics of water-soluble inorganic ions and inorganic metal elements in particles were analyzed,and the difference characteristics of rain and drought seasons were compared.Correlation analysis,principal component analysis and enrichment factor method were used to analyze the sources of water-soluble inorganic ions and inorganic metal elements.Finally,PMF model was used to determine the source of particulate matter.Through comprehensive analysis of atmospheric particulate matter data and results,the pollution characteristics,chemical composition and related sources of atmospheric particulate matter in rain and dry seasons in Lhasa can be scientifically analyzed,which is of profound significance for the prevention and control of air pollution in Lhasa and the protection of population health.This study found that during the sampling period,the air quality of Lhasa was relatively clean,and the mass concentration of particulate matter in dry season was much higher than that in rainy season.In Lhasa,the mass concentration of PM_2.5 in rainy season and dry season is9.64μg/m~3 and 18.38μg/m~3 respectively.The mass concentration of PM₁₀in Lhasa in rainy season and dry season was 16.78μg/m~3 and 37.31μg/m~3,respectively.According to GB3095-2012,all have reached the first-class standard.Compared with the dry season,the concentration of total water-soluble inorganic ions and inorganic metal elements in PM_2.5 and PM₁₀ in rainy season is lower,and the proportion of water-soluble inorganic ions in the mass concentration of particulate matter is higher than that of inorganic metal elements in the mass concentration of particulate matter.The proportion of total water-soluble inorganic ions in PM_2.5 and PM₁₀ in dry season is more than twice that in rainy season,and the proportion of total inorganic metal elements in PM_2.5 and PM₁₀ in dry season is more than twice that in rainy season.Compared with inorganic metal elements,water-soluble inorganic ions are greatly affected by the difference between rainy season and dry season.The main water-soluble inorganic ions of PM_2.5 in rainy season and dry season are SO₄^2-,Mg²⁺and NO₃^-.The main water-soluble inorganic ions in PM_2.5 in dry season also include NH₄⁺and Na⁺.The main water-soluble inorganic ions in PM₁₀ in Lhasa during rainy season and dry season are SO₄^2-,Mg²⁺and NO₃^-,while the main water-soluble inorganic ions in PM₁₀ during dry season also include NH₄⁺and Na⁺.The main metal elements in PM_2.5 and PM₁₀ in rainy and dry seasons are Ca,Na,Fe,Al,K and Mg.The characteristics of particle size distribution in Lhasa indicate that atmospheric particles are influenced by both natural and man-made sources.The particle size distribution of K⁺,Ca²⁺,NO₂^-and NO₃^-in water-soluble ions in rainy season showed a trimodal pattern.The particle size distribution of K⁺,Ca²⁺,Na⁺and Mg²⁺in water-soluble ions in dry season showed a trimodal pattern.The particle size distribution of Na and Ni in rainy season and Zn and Cd in dry season shows a trimodal distribution.These ions and elements come from many sources in rainy season and dry season.The enrichment factor method shows that Cd is a highly enriched element in PM_2.5 and PM₁₀ in rainy and dry seasons.According to a series of correlation analysis and source analysis results,garbage incineration sources,secondary sources,automobile exhaust sources,dust sources,coal burning sources and biomass combustion sources are the main sources of atmospheric particulate matter in Lhasa.Prevention and control of these sources can effectively reduce the concentration of atmospheric particulate matter in Lhasa.