Study On Pollution Law And Chemical Composition Distribution Characteristics Of PM_2.5 In Qiqihar

It is of great practical significance to provide theoretical basis for the development of air pollution control strategy in Qiqihar city by studying the changes of PM_2.5.5 concentration,chemical composition,influencing factors and source characteristics.In order to complete the study of PM_2.5.5 in the city,the study was carried out 24 hours continuous monitoring of Qiqihar area by intelligent sampler between March 1,2016 and February 28,2017,which studied the changes of PM_2.5.5 mass concentration and its relationship with meteorological factors,the characteristics of water soluble ions and inorganic elements in haze weather,the chemical composition and source analysis of PAHs and their health risk evaluation.The experimental results showed:Monitoring results from 2013 to 2016 showed PM_2.5.5 concentration of 50.1 ug/m3 in Qiqihar over four years.Comparison of annual mean mass concentration:PM_{2.5（2013）}（39.6μg/m³）<PM_{2.5（2016）}（45.5μg/m³）<PM_{2.5（2015）}（53.8μg/m³）<PM_{2.5（2014）}（62.3μg/m³）;During the period from 1 March 2016 to 28 February 2017,the highest concentration of PM_2.5.5 was observed in the winter,followed by the autumn,with relatively low levels in spring and summer;The change from March to June showed a downward trend and an upward trend from August to January;The diurnal variation of the seasonal mass concentration of PM_2.5was double peaks.The results of the correlation analysis between PM_2.5.5 mass concentration and various meteorological factors showed that PM_2.5.5 mass concentration was negative correlation with temperature,wind speed,precipitation and horizontal visibility,and positive correlation with air pressure and humidity,which showed that all meteorological factors were closely related to PM_2.5.5 mass concentration.The results of the analysis of the haze showed that the total water-soluble ion concentration in PM_2.5.5 was 73.66μg/m³,which accounted for 35.5%of the mass concentration of PM_2.5.It was assumed that PM_2.5.5 was mainly in the form of（NH₄）₂SO₄,NH₄NO₃,NH₄Cl and K₂SO₄ salts.The overall concentration of elements increased during the haze,with Cr,As,W,Pb increasing 3-6 times,and other elements also increasing to varying degrees.As,W,Pb of the concentration were high,which showed that the source of pollution mainly come from coal burning and motor vehicle emission during heavy smog in Qiqihar.During the period,the mean total PAHs concentration in PM_2.5.5 was 33.32 ng/m³,the total PAHs concentration range was 0.99¹34.17 ng/m³,and the seasonal concentration showed autumn>winter>spring>summer;According to the characteristic ratio method and factor analysis,the pollution of atmospheric particulate matter(PM_2.5)in Qiqihar city was derived from coal combustion,biomass combustion,automobile exhaust gas emission and Coke furnace discharge.According to the health risk evaluation of PAHs,the highest concentration of toxic equivalent in autumn in the four seasons in Qiqihar city indicated that it had the greatest effect on health,with the least effect in summer.There was no overall risk of carcinogenic exposure to pollutants at all ages.