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

Abstract

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 Correspondence to: T. J. Yasunari (teppei.j.yasunari@nasa.gov) 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.

Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

“…The simulated maximum BC content in snow is over the TP, especially the southern slope with concentrations larger than 100 µg kg −1 . The southern slope of the Himalayas is directly exposed to Indian emissions and likely receives more BC than the northern slope via the southwesterly and via the southern branch of the winter westerlies that sweep over the south side of the Himalaya-Hindu Kush range (Kaspari et al, 2007;Xu et al, 2009;Yasunari et al, 2010). As suggested by Menon et al (2010), the emissions of particulate matter in India have been increasing over the last few decades and are expected to increase in the future due to rapid industrial growth and slower emission control measures.…”

“…During late spring and early summer (April through midJune), the increased low-level southwesterly brings in not only additional moisture from the Arabian Sea and Indian Ocean but also aerosols (e.g. dust and BC) from the Indian subcontinent to northern India and the Himalayan foothills, that are possibly deposited over the southern slope of the TP (Yasunari et al, 2010). The enhanced warming over the darkened surface increases the convective instability and spurs deep convection, which further strengthens the low-level southwesterly flow and increases precipitation (Fig.…”

Seasonal Variation, Sources and Transport of Aerosols at Lijiang, Southeast Tibetan Plateau

“…In contrast, the temperature increase rate in the southeastern TP and southwest China was lower than that of the whole of China during 1961-2010, and the most distinguished increasing trend occurred in winter, followed by autumn; however, spring and summer temperatures did not show any significant increasing trend (Ma et al, 2013). South Asia is a major source of black carbon, especially during the pre-monsoon period, which has a significant warming effect on climate, and has been shown to cause snow/ice melt over the TP Lau et al, 2010;Yasunari et al, 2010). Lau et al (2010) also found that the aerosol mixed with dust and black carbon can heat the midtroposphere and accelerate the melting of snow on the western TP.…”

Spring-Time Enhancement in Aerosol Burden over a High-Altitude Location in Western Trans-Himalaya:Results from Long-Term Observations

“…Ji et al 50 have reported that, although seasonal variations in the dry deposition are not significant, the wet deposition rate of carbonaceous aerosols is greater during the non-monsoon seasons than the monsoon season in the northwest Himalayan regions. The efficient long range transport resulting in higher amounts of absorbing aerosols such as BC and dust during spring, and its subsequent deposition on snow and ice-cover, coupled with increased amounts of solar insolation during this season may have strong climate consequences, resulting in atmospheric warming, changes in surface albedo and enhancing the retreat of glaciers 8,55 . Nair et al 8 showed that the diurnally averaged forcing due to snow darkening over Hanle is in the range 0.87-10.2 W m -2 and 2.6-28.1 W m -2 for fresh snow and aged snow respectively, which is significantly higher than the clear sky direct radiative forcing at the top of the atmosphere (1.69 W m -2 over snow surface and -1.54 W m -2 over sandy surface).…”