Pollution Characteristics And Source Apportionment Of Black Carbon Aerosol In Shijiazhuang City

In order to understand the pollution characteristics and sources of black carbon（BC）aerosols in Shijiazhuang,a black carbon meter was used to monitor the mass concentration of BC in the urban（TV Tower site）and suburban（Hebei University of Science and Technology site）area from September 2018 to August 2019 in this study.The time change characteristics of BC mass concentration and the local source of BC combining other pollutant concentration data during the research period was analyzed.Finally,the 48h backward trajectory clustering analysis was performed using the HYSPLIT mode,and the contribution of the airflows from different paths to Shijiazhuang during the study period was obtained.Also,the potential source analysis method（PSCF）and the concentration weighted trajectory analysis method（CWT）were used to analysis the potential source areas of BC in different seasons in Shijiazhuang and the corresponding BC weighted concentration contribution.The main conclusions are as follows:1)The mass concentrations of BC in the urban and suburban areas of Shijiazhuang were（4.82±4.28）μg·m^-3 and（4.35±3.59）μg·m^-3,respectively.The BC mass concentration values were mainly distributed in 0～8μg·m^-3,and the background value was 1.0μg·m^-3.The seasonal variation of BC mass concentration presented the characteristics as winter>autumn>spring>summer.The diurnal variation showed a trend of double peaks and single valley,and peak periods were 6:00～9:00 and 19:00～22:00,the valley period was 13:00～15:00.2)The average value of BC aerosol absorption wavelength indexαwas（1.22±0.21）.The correlation analysis between BC and CO,NO₂,SO₂,and organic carbon and element carbon in PM_2.5,results showed that BC had an extremely correlation with CO during study period,strong correlation with NO₂,SO₂ in spring,autumn and winter,and weak correlation in summer.The ratio of BC/CO(μg·m^-3/ppbv)ranged from 0.0030 to 0.0062,with an average of 0.0049.BC had a strong correlation with EC1,EC2 and OC2 in PM_2.5in autumn and winter.Results showed that coal burning source and motor vehicle exhaust emissions source were the main local emission sources of BC.3)Backward trajectory cluster analysis showed that BC was mainly affected by local sources and near-distance pollution sources transportation air masses,and was less affected by distant pollution sources transportation air masses.The air masses from the East and southeast of Hebei Province and the northwest passing through Northern Shaanxi and central Shanxi have great influence on BC.4)PSCF analysis showed that there were great differences in the potential source areas in different seasons,among which the potential source areas in winter were the most extensive.In CWT analysis,the high value regions of WCWT in each season were similar to the potential source areas of WPSCF.The results showed that the main source areas of BC in Shijiazhuang were the surrounding areas of Shijiazhuang,southern Hebei Province,northern Henan Province,and central and southern Shanxi Province,which mainly included Xingtai,Handan,Baoding,Cangzhou,Anyang,Lvliang,Linfen,Changzhi and so on.