| In this study,the hourly averaged data of black carbon(BC)aerosol in the northern Suburb of Nanjing from January 2015 to December 2016 were applied to analyze the characteristics and influencing factors of BC,and combined with the Aethalometer model,the contributions of fossil fuel and biomass burning sources to the total BC mass concentration were apportioned.Moreover,HYSPLIT model and concentration-weighted trajectory(CWT)to study the spatial characteristics of different transport pathways,identify the potential source zones and its contribution to BC during different seasons.The main conclusions are as follows.(1)Daily mean BC concentration was 2200±1309 ng/m3 for the entire period,while the concentration decreased significantly in 2016 by about 30%on average when compared to that in 2015.The frequency distribution of BC in different seasons showed that the occurrence of BC heavy pollution events were significantly higher in winter than in other seasons.A distinct diurnal variation of BC with two peaks occurred,one in the morning during 06:00?09:00and another in late evening during 19:00?22:00 local time,which was strongly associated with anthropogenic activities and the dynamics of atmospheric boundary layer.(2)The correlation coefficients between BC,NOx and PM2.5 were 0.67 and 0.61,respectively.A lower rate of ABC/ACO was found in the northern suburb of Nanjing,suggesting that biomass burning emission may be another important source of BC in here.The correlation analysis between BC and wind speed shows that BC concentration decreased significantly with wind speed increased at the speed of 1?3m/s.However,when the wind speed was more than 3m/s,the trend between BC and wind speed was not obvious.Diurnal changes of BC and boundary layer height were negatively correlated in each season,and the boundary layer height was higher in clean days than that in polluted days,it is shown that the dynamic effect of boundary layer plays an important role in the variation of BC.(3)The daily average absorption coefficient and extinction coefficient varied from 10.5 to 199.1 Mm-1 and 127.9 to 1764.3 Mm-1 respectively,and the percentage of their ratio was 12.6%with the range between 10.5 and 199.1 Mm-1 during the period.BC concentration was higher in haze and heavy haze weather,which were 2 and 2.3 times as large as in non-haze weather,respectively.(4)The Angstrom absorption exponent(a)was highest in winter and lowest in summer.Similarly with the patterns of a,a lower level of the percentage contribution of BCbb(BCbb%)in summer and higher levels of BCbb%in spring and winter,which suggests that the contribution of biomass burning has increased except for the existing fossil fuel emissions during spring and winter.The concentrations of BCff and BCbb were maximum in winter,while the concentrations were relatively lower and the values were close in other seasons.The contribution of BCff to total BC was higher than 75%in each season,and dominated by BCff throughout the observation,which demonstrates that fossil fuel combustion was the main source of BC in the north suburb of Nanjing.(5)There were striking discrepancies of airflow trajectory among different seasons,in spring and summer,the airflows from ocean occupied a large proportion and corresponded to low BC concentration,while the airflows from northwest inland area accounted for a high proportion,corresponding to the high BC concentration.Meanwhile,the CWT analysis signifies that the highest value of BC was concentrated in Zhejiang,Anhui,Jiangxi and Fujian province.Besides,Henan and Shandong province were also the potential source areas of BC in Nanjing. |
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