[1] Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high-altitude station, Manora Peak in central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of central Himalayas and having a monthly mean AOD (at 500 nm) of 0.059 ± 0.033 (typical to this site), total suspended particulate (TSP) concentration was in the range 15-40 mg m À3 (mean value 27.1 ± 8.3 mg m À3 ). Interestingly, aerosol BC had a mean concentration of 1.36 ± 0.99 mg m À3 and contributed $5.0 ± 1.3% to the composite aerosol mass. This large abundance of BC is found to have linkages to the human activities in the adjoining valley and to the boundary layer dynamics. Consequently, the inferred single scattering albedo lies in the range of 0.87 to 0.94 (mean value 0.90 ± 0.03), indicating significant aerosol absorption. The estimated aerosol radiative forcing was as low as À4.2 W m À2 at the surface, +0.7 W m À2 at the top of the atmosphere, implying an atmospheric forcing of +4.9 W m À2 . Though absolute value of the atmospheric forcing is quite small, which arises primarily from the very low AOD (or the column abundance of aerosols), the forcing efficiency (forcing per unit optical depth) was $88 W m À2 , which is attributed to the high BC mass fraction.

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Abstract.A long-term study, conducted from February 2005 to July 2008, involving chemical composition and optical properties of ambient aerosols from a high-altitude site (Manora Peak: 29.4 • N, 79.5 • E, ∼1950 m a.s.l.) in the central Himalaya is reported here. The total suspended particulate (TSP) mass concentration varied from 13 to 272 µg m −3 over a span of 42 months. Aerosol optical depth (AOD) and TSP increase significantly during the summer (AprilJune) due to increase in the concentration of mineral dust associated with the long-range transport from desert regions (from the middle-East and Thar Desert in western India). The seasonal variability in the carbonaceous species (EC, OC) is also significantly pronounced, with lower concentrations during the summer and monsoon (July-August) and relatively high during the post-monsoon (September-November) and winter (December-March). On average, total carbonaceous aerosols (TCA) and water-soluble inorganic species (WSIS) contribute nearly 25 and 10% of the TSP mass, respectively. The WSOC/OC ratios range from 0.36 to 0.83 (average: 0.55 ± 0.15), compared to lower ratios in the IndoGangetic Plain (range: 0.35-0.40), and provide evidence for the enhanced contribution from secondary organic aerosols. The mass fraction of absorbing EC ranged from less than a percent (during the summer) to as high as 7.6% (during the winter) and absorption coefficient (b abs , at 678 nm) varied between 0.9 to 33.9 Mm −1 (1 Mm −1 =10 −6 m −1 ). A significant linear relationship between b abs and EC (µgC m −3 ) yields a slope of 12.2 (± 2.3) m 2 g −1 , which is used as a measure of the mass absorption efficiency (σ abs ) of EC.

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[1] The influences of the springtime northern Indian biomass burning are shown for the first time over the central Himalayas by using three years (2007)(2008)(2009) . These biomass burning induced changes over the central Himalayan atmosphere during spring may also lead to enhanced short-wave absorption above clouds and might have an impact on the monsoonal rainfall.