Characteristics,Source Analysis And Heavy Metal Risk Assessment Of Atmospheric PM₁₀ Pollution In Yan’an Urban Area During Heating Period

In recent years,the characteristics of air pollution in China have changed from traditional coal smoke pollution to composite pollution with primary and secondary,local and regional coexistence of inhalable particulate matter(PM₁₀),fine particulate matter(PM_2.5)and gaseous pollutants.Air pollution is getting worse,especially during the heating period in the north.In this study,PM₁₀ environmental receptor samples were collected at four points（JCZ,BMDD,YDFY,ZY）in the main urban area of Yan’an city from December 22 to December 28,2020.By analyzing the pollution characteristics of their mass concentration and chemical components,PMF model was used to determine the source of pollutants.The potential ecological risk index method and health risk assessment model were used to evaluate the potential ecological risk and respiratory health risk of heavy metals.The main results and conclusions obtained are as follows:（1）The results showed that during the sampling period,the mass concentration of atmospheric particulate matter PM₁₀ in Yan’an city ranged from 53.99 to 199.72μg/m³,and the average concentration was（102.65±42.04）μg/m³,which did not exceed the second-level daily standard limit of China’s Ambient Air Quality Standard（GB3095-2012）.The average concentration of water-soluble ions was（35.54±11.13）μg/m³,accounting for 34.62%of PM₁₀.Among them,secondary inorganic ions（SNA）is the main pollution component,accounting for 60.78%of the total ion concentration.In addition,the mass concentration of Ca²⁺is also high,and the dust pollution is more serious.The results of NO₃^-/SO₄^2-ratio show that the pollution of yan’an urban area in heating period is affected by both mobile source and fixed source emissions.The results of SOR and NOR indicated that there was a secondary oxidation process of SO₂ and NO₂.The average concentration of inorganic elements was（12.65±4.48）μg/m³ accounting for12.33%of PM₁₀.The enrichment factor analysis showed that Na,Ca,Cr,Ni,Cu,Zn,As,Cd and Pb mainly came from human sources,and the human pollution of Cd and Pb was the most serious.The average concentrations of OC and EC were（14.65±4.01）μg/m³ and（2.96±0.57）μg/m³,accounting for 14.27%and 2.89%of PM₁₀,respectively.The ratio of OC/EC indicated that secondary organic carbon pollution was prevalent.The average concentration of SOC was（4.67±3.18）μg/m³,accounting for 29.6%of OC and 4.55%of PM₁₀,among which the monitoring station had the highest mass concentration of SOC.（2）PMF source analysis results show that,The main pollution sources of PM₁₀ in Yan’an city during heating period were secondary inorganic sources and biomass combustion sources（33.53%）,soil dust sources（30.18%）,motor vehicle emission sources（9.89%）,coal and industrial sources（7.55%）,road dust sources（15.79%）and other unsolved sources（3.07%）.（3）According to the human health risk assessment of heavy metals,the HQ values of non-carcinogenic heavy metals for the three groups were Mn>V>Cu>Fe>Zn in the order of respiratory exposure,and the non-carcinogenic risk of each heavy metal for children was higher than that for adult males and females.Mn has significant non-carcinogenic risk to three groups of people.The order of carcinogenic elements is Cr>As>Ni>Cd.Among them,Cr has unacceptable carcinogenic risk to adult male and female.（4）The potential ecological risk assessment results of heavy metals show that the potential ecological hazard coefficient（Er）of Cd in PM₁₀ during the heating period of Yan’an urban area is the largest,followed by Pb,Ni and Cu,which have a higher potential hazard risk to ecology.The combined potential ecological risk index（RI）of the 10 heavy metals is much larger than the standard level,which has a greater impact on local ecological risks.