Articles | Volume 10, issue 14
Atmos. Chem. Phys., 10, 6603–6615, 2010

Special issue: Atmospheric brown cloud in the Himalayas

Atmos. Chem. Phys., 10, 6603–6615, 2010

  19 Jul 2010

19 Jul 2010

Estimated impact of black carbon deposition during pre-monsoon season from Nepal Climate Observatory – Pyramid data and snow albedo changes over Himalayan glaciers

T. J. Yasunari1,2, P. Bonasoni3,4, P. Laj5, K. Fujita6, E. Vuillermoz4, A. Marinoni3, P. Cristofanelli3, R. Duchi3, G. Tartari7, and K.-M. Lau1 T. J. Yasunari et al.
  • 1NASA Goddard Space Flight Center, Greenbelt, USA
  • 2Goddard Earth Science and Technology Center, University of Maryland Baltimore County, Baltimore, USA
  • 3CNR – Institute for Atmospheric Sciences and Climate, Bologna, Italy
  • 4Ev-K2-CNR Committee, Bergamo, Italy
  • 5Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Grenoble 1 – CNRS (UMR5183), St. Martin d'Heres, France
  • 6Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 7CNR – Water Research Institute, Brugherio, Italy

Abstract. The possible minimal range of reduction in snow surface albedo due to dry deposition of black carbon (BC) in the pre-monsoon period (March–May) was estimated as a lower bound together with the estimation of its accuracy, based on atmospheric observations at the Nepal Climate Observatory – Pyramid (NCO-P) sited at 5079 m a.s.l. in the Himalayan region. A total BC deposition rate was estimated as 2.89 μg m−2 day−1 providing a total deposition of 266 μg m−2 for March–May at the site, based on a calculation with a minimal deposition velocity of 1.0×10−4 m s−1 with atmospheric data of equivalent BC concentration. Main BC size at NCO-P site was determined as 103.1–669.8 nm by correlation analyses between equivalent BC concentration and particulate size distributions in the atmosphere. The BC deposition from the size distribution data was also estimated. It was found that 8.7% of the estimated dry deposition corresponds to the estimated BC deposition from equivalent BC concentration data. If all the BC is deposited uniformly on the top 2-cm pure snow, the corresponding BC concentration is 26.0–68.2 μg kg−1, assuming snow density variations of 195–512 kg m−3 of Yala Glacier close to NCO-P site. Such a concentration of BC in snow could result in 2.0–5.2% albedo reductions. By assuming these albedo reductions continue throughout the year, and then applying simple numerical experiments with a glacier mass balance model, we estimated reductions would lead to runoff increases of 70–204 mm of water. This runoff is the equivalent of 11.6–33.9% of the annual discharge of a typical Tibetan glacier. Our estimates of BC concentration in snow surface for pre-monsoon season is comparable to those at similar altitudes in the Himalayan region, where glaciers and perpetual snow regions begin, in the vicinity of NCO-P. Our estimates from only BC are likely to represent a lower bound for snow albedo reductions, because we used a fixed slower deposition velocity. In addition, we excluded the effects of atmospheric wind and turbulence, snow aging, dust deposition, and snow albedo feedbacks. This preliminary study represents the first investigation of BC deposition and related albedo on snow, using atmospheric aerosol data observed at the southern slope in the Himalayas.

Final-revised paper