Pollution characteristics and health risk assessment of metal elements in atmospheric PM2.5 in Lanzhou
Background,aim,and scope In the northwest region of China,Lanzhou City serves as a significant industrial hub,characterized by substantial pollutant emissions.The combination of spring dust storms,winter heating activities,and terrain that impedes pollutant dispersion makes the city prone to severe air pollution events.This study analyzes the concentrations of 10 metal elements in PM2.5 within Chengguan District and Xigu District of Lanzhou City in 2020.The research aims to elucidate the pollution characteristics and conduct a health risk assessment of these metal elements.The findings offer a scientific basis for developing strategies to control air pollution in Lanzhou City and contribute to the improvement of the atmospheric environment.Materials and methods A medium-flow atmospheric particulate sampler was employed to collect samples from Changjiaxiang Primary School in Chengguan District and Yumenjie Primary School in Xigu District over a one-year period,with a sampling height of 10 m.Quartz filter membranes were utilized to capture fine particulate matter.Following microwave digestion of PM2.5 samples,Inductively Coupled Plasma Mass Spectrometry(ICP/MS)was used to quantify the concentrations of 10 metal elements in PM2.5.The data were analyzed using positive matrix factorization(PMF)models to identify pollution sources,and U.S.Environmental Protection Agency(EPA)exposure models were applied for health risk assessment.Results The average annual mass concentrations of PM2.5 in Chengguan District and Xigu District were 48.21 μg·m-3 and 49.33 μg·mr-3,respectively.The total concentrations of the 10 analyzed metal elements were 241.03 ng·m-3 in Chengguan District and 296.80 ng·m-3 in Xigu District,with Al,Mn,and Pb being the predominant components in both regions.Analysis using PMF model identified four primary pollution sources in Chengguan District:industrial sources,coal/motor vehicle mixed sources,agricultural sources,and industrial/dust mixed sources.In Xigu District,three main pollution sources were identified:industrial sources,industrial/dust mixed sources,and coal/motor vehicle mixed sources.In both regions,industrial/dust mixed sources constituted the largest proportion,with industrial sources and coal/motor vehicle mixed sources also contributing significantly.Health risk assessments indicated that the non-carcinogenic hazard quotient(HQ)for each element in both districts was less than 1,suggesting negligible non-carcinogenic risk.Additionally,the carcinogenic risks associated with Cr,Ni,As,and Cd did not exceed the threshold of 10-4.Discussion With the rapid development of China's economy and society,atmospheric metal element pollution has become a pervasive and serious issue.This paper examines the characteristics of metal element pollution in atmospheric PM2.5 in Lanzhou City.The study reveals a high degree of variability in the concentrations of metal elements in atmospheric PM2.5,largely influenced by human activities.In both Chengguan District and Xigu District,Al,Pb,Mn,and As constituted 97.21％and 97.64％of the total concentration of the 10 analyzed elements,respectively.PM2.5 concentration in Lanzhou City exhibited significant seasonal variation.Notably,the concentrations of Pb,As,Cd,and Se increased substantially in winter,likely due to coal heating.The highest Al concentrations were recorded in spring,potentially attributed to frequent dust storms and stable wind conditions in northwest China,leading to lower Al concentrations in other seasons.Industrial and dust mixed sources were identified as the primary pollution contributors.Although the non-carcinogenic risk of all elements was below the threshold,the carcinogenic risks of four elements(Cr,Ni,As,and Cd)necessitate mitigation.This study focuses on atmospheric PM2.5 metal elements in Chengguan District and Xigu District,without specific assessment or comparison of pollution in other areas of Lanzhou City.Therefore,while it does not comprehensively reflect the background concentration across the entire city,it does represent the overall pollution level to a certain extent.PMF model was employed to analyze the pollution sources of metal elements.Health risk assessments were conducted to evaluate the carcinogenic and non-carcinogenic risks of these elements,providing insights into the mechanisms of metal element pollution.These findings can serve as a reference for formulating effective atmospheric control measures and policies.Conclusions PM2.5 concentration in Lanzhou City exceeds the annual average concentration limit set by the national secondary standard(35 μg·m-3).The primary sources of pollution are mixed industrial/dust sources,industrial sources,and coal/motor vehicle mixed sources.The analysis of 10 metal elements in PM2.5 indicates that there is no non-carcinogenic risk associated with these elements.Additionally,the carcinogenic risk for four elements is within the acceptable range.Recommendations and perspectives Measures should be implemented to prevent and control air pollution and to reduce the concentration of PM2.5,particularly the toxic metal elements in PM2.5.Efforts should focus on strengthening the regulation of industrial and traffic-related emissions,expanding green vegetation areas,and striving to improve the atmospheric environment in Lanzhou.
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