Temporal Variation And Source Analysis Of Black Carbon Aerosol In Wuhan

Black Carbon is the main light-absorbing aerosol and plays an important role in Earth's climate system.Different from other scattering aerosol,BC has a strong absorption of solar radiation in a wide band.Absorption by BC is thought to comparable to the cooling associated with sulfate aerosols.Acting as the second most vital component of global warming after CO2,BC impacts on climate change through direct and indirect radiative forcing.BC can also influences cloud processes and alters the melting of snow and ice cover.Due to its unique physical and chemical properties,BC can promote the occurrence of environmental pollution and seriously endangers human health.AE-31 is the most wildly used real-time measuring instrument of BC concentration.In order to eliminate the error caused by filter-loading effect,we used the correction method provided by Virkkula.The corrected data can maintain good continuity during the movement of the filter belt.The correction factor we propose in every season is 0.00175 for autumn,0.00328 for winter,0.00113 for spring and 0.00124 for summer.In this study continuous measurement of BC are made in an urban site in Wuhan form September 2013 to August 2014.The annual mean BC concentration is found to be 5.01 ± 2.93 ?g/m3.The BC concentrations vary from season change.The averaged BC concentration in polluted days of Winter is the highest and the value is 8.96 ± 2.77 ?g/m3.The value in clear days of Winter is 3,08 ± 1.62?g/m3.The averaged BC concentrations in Autumn,Spring and Summer are respectively 5.49 ± 2.64,3.89 ± 1.66 and 3.41 ± 1.54 ?g/m3.The diurnal variations in four seasons show a biomodal distribution.BC levels are high in rush hours(7-9 o'clock am and 8-10 o'clock pm)but low in afternoon(2-3 o'clock pm).Wuhan has experienced a long term pollution from December 2013 to January 2014.Aimed at this pollution incident,we compare BC with other pollutants from synchronized observations.The correlation coefficient of BC and PM2.5 is 0.68449.The high correlation indicates the BC is an important component of PM2.5.The correlation coefficient of BC and CO is 0.68997 and of BC and NO2 is 0.49659.There is a negative correlation between BC and O3.According to the result,we find that fossil fuel burning,biomass combustion and vehicle emission are the major sources of BC in Wuhan.We also use HYSPLIT-4 backward trajectory to get the air transport process during the pollution period.The results show that northern haze,straw burning from peripheral provinces and local emission are all contribute to the pollution in the winter of Wuhan.Combined with simultaneous observation of lidar,we find that BC and ABLH shows a opposite variation tendency and conclude that BC can effectively curb the development of aerosol boundary layer.