摘要
Black carbon（BC） particles play a unique and important role in earth’s climate system.BC was measured（in-situ） in the central part of the Indo-Gangetic Plains（IGP） at Varanasi,which is a highly populated and polluted region due to its topography and extensive emission sources.The annual mean BC mass concentration was 8.92 ± 7.0 μg m-3,with 34%of samples exceeding the average value.Seasonally,BC was highest during the post-monsoon and winter periods（approximately 18 μg m-3） and lower in the premonsoon/monsoon seasons（approximately 6 μg m-3）.The highest frequency（approximately 46%） observed for BC mass was in the interval from 5 to 10 μg m-3.However,during the post-monsoon season,the most common values（approximately 23%） were between 20 and 25 μg m-3.The nighttime concentrations of BC were approximately twice as much as the daytime values because of lower boundary layer heights at nighttime.The Angstrom exponent was significantly positively correlated（0.55） with ground-level BC concentrations,indicating the impact of BC on the columnar aerosol properties.The estimated mean absorption Angstrom exponent was 1.02 ± 0.08 μg m-3,indicating that the major source of BC was from fossil fuel combustion.Significant negative correlations between BC mass and meteorological parameters indicate a pronounced effect of atmospheric dynamics on the BC mass in this region.The highest mean BC mass concentration（18.1 ± 6.9 μg m-3） as a function of wind speed was under calm wind conditions（38%of the time）.
Black carbon（BC） particles play a unique and important role in earth’s climate system.BC was measured（in-situ） in the central part of the Indo-Gangetic Plains（IGP） at Varanasi,which is a highly populated and polluted region due to its topography and extensive emission sources.The annual mean BC mass concentration was 8.92 ± 7.0 μg m-3,with 34%of samples exceeding the average value.Seasonally,BC was highest during the post-monsoon and winter periods（approximately 18 μg m-3） and lower in the premonsoon/monsoon seasons（approximately 6 μg m-3）.The highest frequency（approximately 46%） observed for BC mass was in the interval from 5 to 10 μg m-3.However,during the post-monsoon season,the most common values（approximately 23%） were between 20 and 25 μg m-3.The nighttime concentrations of BC were approximately twice as much as the daytime values because of lower boundary layer heights at nighttime.The Angstrom exponent was significantly positively correlated（0.55） with ground-level BC concentrations,indicating the impact of BC on the columnar aerosol properties.The estimated mean absorption Angstrom exponent was 1.02 ± 0.08 μg m-3,indicating that the major source of BC was from fossil fuel combustion.Significant negative correlations between BC mass and meteorological parameters indicate a pronounced effect of atmospheric dynamics on the BC mass in this region.The highest mean BC mass concentration（18.1 ± 6.9 μg m-3） as a function of wind speed was under calm wind conditions（38%of the time）.
基金
Supported by the Indian Space Research Organization(ISRO)"Aerosol Radiative Forcing over India"Program at Bananas Hindu University(P32/15 and P32/14)
