We present the systematic analysis of individual black carbon (BC) mixing state and its impact on radiative forcing from an urban Indian city, Kanpur, located in Indo-Gangetic Plain (IGP). Simultaneous measurements using Single Particle Soot Photometer (SP2), Photo-Acoustic Soot Spectrometer (PASS-3) and High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) were conducted from 8 January 2015 to 28 February 2015 at Kanpur. BC mass and number concentrations varied between 0.7 and 17 mu g/m(3) and 277-5866 #/cm(3) with a mean of 4.06 mu g/m3 and 1314 #/cm3, respectively. The diurnal variation of BC mass concentration showed a traffic hour peak during both the morning and late night. The mean fraction of thickly coated BC particles (fTC(Bc)) was found to be 61.6%, indicating that a large fraction of BC particles was internally mixed. The fTCBc increased after sunrise with a peak at about noontime, indicating that the formation of secondary organic aerosol under active photochemistry can enhance organic coating on a core of black carbon. High-resolution positive matrix factorization (HR-PMF) factors showed distinct characteristics with fTCBc. While primary organic aerosols like cooking organic aerosols (COA) and biomass burning organic aerosols (BBOA) were negatively correlated with fTCBc = -0.78 and -0.51, respectively), aged low volatile oxygenated organic aerosol (LVOOA) was forming a coating over BC (r = 0.6). Similar positive correlation of fTCBc with inorganic species like ammonium (r = 0.58) and nitrate (r = 0.47) further suggested that BC appears to be largely coated with LVOOA, ammonium, and nitrate. A positive correlation between the fTCBc and the mass absorption cross-section at 781 nm (MAC(781)) was also observed (r = 0.58). Our results suggest that the observed fTCBc could amplify the MAC781 approximately by a factor of 1.8, which may catalyze the positive radiative forcing in the IGP.

来源平台：ATMOSPHERIC RESEARCH