| Atmosphere is of important environment for human beings.The composition of atmosphere not only reflects the biological and geographical processes,but also provides necessary requirements for survival of plants and animals on the Earth.Dramatic changes of urbanization and industrialization has taken place since the last industrial revolution.With the rapid economic development,the earth environment has suffered significant pollution in the past few decades.PM2.5 pollution is one of the severe environmental issues that plagues the humans.PM2.5 not only alters people's life,but also poses a great threat to people's health.Therefore,the characteristics of PM2.5pollution of urban atmospheric environment and associated influencing mechanism have attracted much attention.In this study,three typical cities including Beijing,Jinan,and Shanghai were selected.Long time sampling acticities were implemented simultaneously from November,2014 to October,2015.The meteorological data and gas pollution data were obtained from China Meteorological Adminstration and Ministry of Ecology and Environment of China,respectively.The seasonal distribution of PM2.5,the relationships between environmental factors and PM2.5 concentration,the distribution,source and potential health risk of PM2.5-bound PAHs were investigated in this study.The average PM2.5 concentrations in Beijing were 125.71±91.14?g/m3,89.83±58.43?g/m3,77.13±54.66?g/m3,and 92.20±121.54?g/m3 in winter,spring,summer and fall,respectively.The average concentrations of PM2.5 in winter were significantly higher than those in other three seasons.There were coal-fired heating acativities in winter compared to the other seasons,which indicated that coal combustion was the main factor for the high concentration of PM2.5 in winter.The average PM2.5concentrations in Jinan were 113.86±62.66?g/m3,98.64±45.24?g/m3,110.31±60.48?g/m3,and 110.02±70.22?g/m3 in winter,spring,summer and fall,respectively.The concentrations of PM2.5 were lightly higher in winter than those in other seasons in Jinan,which was attributed to the coal combustion for heating in winter.However,the difference in PM2.5 concentration did not differed across the four seasons.The reason was that there is a large amount of coal burning in four seasons,and the industrial coal consumption accounts for 49.61%of the total coal consumption in Jinan.Thus,industrial coal burning was the main factor for the high concentration of PM2.5 in all four seasons in Jinan.The average PM2.5 concentrations in Shanghai were 86.26±43.29?g/m3,58.90±27.98?g/m3,48.85±24.48?g/m3,and 51.00±31.27?g/m3 in winter,spring,summer and fall,respectively.The concentrations of PM2.5 in winter were significantly higher than that in the other three seasons.However,there was no coal-fired heating activity in Shanghai in winter.The high concentrations of PM2.5 in winter was attributed to the contributions of long-distance transport of atmospheric particulate matter from surrounding provinces and cities.The proportion of PM2.5 in PM10accounted for more than 50%in these cities,indicating that PM2.5 was the main particulate matter in PM10.According to the air quality standard?GB3095-2012?,the ratios of PM2.5 concentration being lower than the national second-class standard?35?g/m3?were 50.26%?96/191?,27.75%?53/191?and 71.22%?143/205?in Beijing,Jinan,and Shanghai,respectively.Overall,among the three typical cities,Jinan had the highest PM2.5 pollution level,followed by Beijing and Shanghai.The relationship between different meteorological parameters and PM2.5.5 concentration shows that the height of planetary boundary layer?PBL?was negatively correlated with the concentration of PM2.5.The lower the PBL at night,the more unfavorable diffusion of pollutants conducived to the occurrence of chemical reactions,and the large number of secondary particle pollutants could lead to the increase of PM2.5 concentration at night.The influence of temperature on PM2.5 concentrations can be classified as the following aspects.Firstly,by changing human activity:when temperatures were low in the winter,coal combustion was used for heating,and the burning of large amounts of coal and other fuels will induce the bad air quality.Secondly,temperature can also affect the formation of PM2.5 by changing chemical reactions in the atmosphere:sunlight intensity was generally high when the temperature is high,and secondary particulate matter was generated by photochemical reactions can aggravate PM2.5 pollution.The influences of relative humidity on PM2.5 can be concluded into two aspects:when there is no precipitation event,the higher the relative humidity is,the higher the concentration of PM2.5 will be.When relative humidity rises to a certain extent,precipitation events will occur,and PM2.5 in the atmosphere will be cleaned.There was a negative correlation between wind speed and PM2.5 concentration:the smaller the wind speed,the more conducive to the formation and accumulation of PM2.5 in the city was;the higher the wind speed,the better condition for scavenging the PM2.5 in the city was.Wind direction,urban industrial layout and topography will influence the formation of PM2.5.In winter,when the PM2.5 pollution was relatively severe,there are industrial factories in the upwind direction in Beijing,Jinan and Shanghai.The prevailing wind will blow air pollutants to the downtown area,and the downwind of the prevailing wind in Beijing and Jinan is mountainous area,which will block the diffusion of PM2.5.The relationships between gas pollutants,PM2.5 concentration,and characteristic of typical ion pollutants in PM2.5 revealled that the concentrations of SO2,NO2,and PM2.5-bound SO42-,NO3-,Cl-were significant higher in coal combustion seasons than that in non-coal combustion seasons,which indicated that fossil fuels combustion during coal combustion season was the main source of these pollutants.In addition,the vehicle emission was another source of NO2.The atmospheric environments converted SO2 and NO2 to SO42-and NO3-by multiple pathways,which were the main source of PM2.5 in urban atmosphere.At last,the ozone was negatively related to PM2.5,indicating that ozone was not the main cause of urban PM2.5 pollution.The concentrations of PM2.5-bound PAHs in three typical cities were winter>spring>fall>summer.Middle Molecular Weight?MMW?amd High Molecular Weight?HMW?PAHs were the major composition in winter,whereas the Low Molecular Weight?LMW?and MMW PAHs were major composition in other seasons in all three cities.This result indicated that the major source of PAHs in winter was combustion.Source appointment analysis indicated that fossil fuel combustion,vehicle emission,and biomass combustion were three major source of PM2.5-bound PAHs in urban area.The potential health risk of PAHs was analysed based on the ILCR?incremental lifetime cancer risk?value for ingestion,inhalation,skin absorption,and total ILCR in different age groups.The result showed that there was no carcinogenic risk for individual exposure pathways for infants,kids,children,teens,and adults in all three cities.However,the total cancer risk of three exposure pathways showed that children,teens and adults in Beijing had cancer risk in four seasons,and kids had cancer risk in winter.Adults in Jinan had cancer risk in four seasons,children and teens had cancer risk in winter,summer and autumn,while kids had cancer risk in winter and autumn.All age groups of people in Shanghai had no cancer risk in all seasons in this study. |
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