Pollution Characteristics,Source Apportionment And Health Risk Assessment Of PM_2.5 In 2018 In Zhengzhou

In recent years,with the rapid development of urbanization and industrialization,atmospheric environmental problems have become increasingly complex.PM_2.5 is considered to be the root cause of decreased atmospheric visibility,increased haze and environmental degradation.To understand the pollution characteristics of atmospheric particulates in process of urban development,PM_2.5 samples were analyzed from 9national control monitoring sites and 3 different functional areas in 2018 in Zhengzhou.This study conducted a comprehensive and systematic study on the pollution characteristics,spatiotemporal changes,regional transmission,source apportionment and health risk assessment of PM_2.5,and conducted in-depth exploration of the different pollution levels and typical heavy pollution processes of PM_2.5.Results showed that the annual average concentration of PM_2.5 was 65.3±55.1μg/m³ in 2018,1.9 times higher than the Chinese grade II annual limits.The seasonal mean PM_2.5 levels had obvious variations with the highest value in winter and the lowest value in summer.The hourly values of PM_2.5 at the national control sites showed a bimodal distribution,with the concentrations at night significantly higher than those during the day.In addition,PM_2.5,PM₁₀,SO₂,NO₂ and CO all had significant positive correlations,indicating from the simlar sources.Coal combustion and secondary formation were the main sources of PM_2.5 in Zhengzhou,especially they contributed the most to PM_2.5 in winter.Compared with previous years,the contributions of coal combustion decreased with the contributions of traffic sources increasing year by year.The proportions of water-soluble inorganic ions（WSIIs）,carbonaceous components and inorganic elements in PM_2.5 were 49.4%,20.1%and 16.2%,respectively.Secondary inorganic ions contributed the most to PM_2.5,and NO₃^-accounted for 33.3%of the total WSIIs concentration.With the increase of PM_2.5pollution level,the proportion of WSIIs increased significantly,with the ratios of NO₃^-,NH₄⁺and Cl^-to PM_2.5 dramatic increasing,indicating coal source and vehicle source playing more and more important roles to PM_2.5 during periods of heavy pollution, while the proportion of carbonaceous components and inorganic elements decreased obviously.In addition,high temperature and humidity,low wind speed and precipitation were important meteorological factors that cause heavy pollution of PM_2.5.According to the health risk assessment of heavy metals,ingestion exposure had unacceptable carcinogenic risks for adult men,adult women and children.PMF results showed that secondary inorganic aerosols（37.6%）,coal combustion（15.4%）,vehicle（13.3%）,SOA（12.3%）,dust（7.8%）,biomass burning（7.5%）and industrial emission（6.0%）were main sources of atmospheric PM_2.5 in Zhengzhou.Backward trajectory cluster analysis results showed that the polluted air masses mainly came from the northwest,with the potential pollution source areas of PM_2.5 mainly distributed in Luoyang,Jiaozuo,Jiyuan,Anyang,Pingdingshan and neighboring provinces（i.e.,Shanxi,Shanxi,Shandong and Beijing-Tianjin-Hebei）.Obviously,the short-distance transmission contributes significantly to the mass concentration of PM_2.5in Zhengzhou.