Light Absorption Of Black Carbon At Mt.Tai And Typical Urban Area In North China Plain

The estimates of radiative forcing of black carbon(BC)remain great uncertainty,largely due to variations in the absorption enhancement of BC by mixingwith organic and inorganic coatings in ambient aerosols.Directly determination of BC EMAC of ambient aerosols requires experimentally removing coating materials including both inorganic salts and organic matter in ambient aerosols.The mass absorption cross-section(MAC)of BC aerosols was determined before and after the coating removal.And most widely three different thermal-optical temperature protocols give a wide EC variation owing to inaccurate correction of pyrolytic char.It called that a two-step removal treated of organic and inorganic matter is required in this study.Meanwhile the study aims to find an optimal thermal analysis protocol for EC samples at urban and rural area,Jinan and Mt Tai,in the North China Plain(NCP)and improve measurement of BC EMAC that were achieved by comparing:NIOSH,EUSAAR and IMPROVE.Negative and positive EC bias affecting carbon measurement were given by NIOSH and IMPROVE.-580? was too low in pure He of IMPROVE,leading to some OC carried over into He/O2 step and detected alongside either PC or native EC.In contrast,due to the highest temperature(870?)in last step of NIOSH,light-absorbing substances prematurely evolve at this step.The treated results of EUSAAR with optimum 650? as maximum temperature and longer OC1-OC2 times in low temperature(200-300?),almost give the real EC concentrations(1.64±0.89ug/cm2)applied to correct MAC of all protocols.The corrected EUSAAR MAC for Jinan and Mt Tai atmospheric BC aerosols Jinan and Mt Taipure of 3.84±0.90 m2g-1 and 3.79±0.10 m2g-1(Average and 1SD)at 678 nm wavelength are basically consistent with the results of Mie theory for fresh BC(3.94-4.80 m2/g-1)and the corrected EUSAAR MAC were enhanced to 7.39±2.60 m2g-1 and 7.81±2.71 m2g-1 at 678nm wavelength for Jinan and Mt Tai coated BC aerosols respectively.Non-BC coatings could enhance the light absorption of BC by a factor of 2 of one day for the NCP campaign aerosols.The enhanced BC absorption was controlled by various factors for Jinan,a heavily polluted city,where pollution source is relatively complex.The light absorption of BC may be rapidly enhanced from air pollution in severely polluted area.EMAC basically remain constant for aging aerosol at Mt Tai where higher aerosol concentration was increased by air masses from the surrounding and urban areas.