Concentrations and source regions of light-absorbing particles in snow/ice in northern Pakistan and their impact on snow albedo

Abstract

Abstract. Black carbon (BC), water-insoluble organic carbon (OC), and mineral dust are important particles in snow and ice which significantly reduce albedo and accelerate melting. Surface snow and ice samples were collected from the Karakoram-Himalayan region of northern Pakistan during 2015 and 2016 in summer (six glaciers), autumn (two glaciers), and winter (six mountain valleys). The average BC concentration overall was 2130 ± 1560 ng g −1 in summer samples, 2883 ± 3439 ng g −1 in autumn samples, and 992 ± 883 ng g −1 in winter samples. The average waterinsoluble OC concentration overall was 1839 ± 1108 ng g −1 in summer samples, 1423 ± 208 ng g −1 in autumn samples, and 1342 ± 672 ng g −1 in winter samples. The overall concentration of BC, OC, and dust in aged snow samples collected during the summer campaign was higher than the concentration in ice samples. The values are relatively high compared to reports by others for the Himalayas and the Tibetan Plateau. This is probably the result of taking more representative samples at lower elevation where deposition is higher and the effects of ageing and enrichment are more marked. A reduction in snow albedo of 0.1-8.3 % for fresh snow and 0.9-32.5 % for aged snow was calculated for selected solar zenith angles during daytime using the Snow, Ice, and Aerosol Radiation (SNICAR) model. The daily mean albedo was reduced by 0.07-12.0 %. The calculated radiative forcing ranged from 0.16 to 43.45 W m −2 depending on snow type, solar zenith angle, and location. The potential source regions of the deposited pollutants were identified using spatial variance in wind vector maps, emission inventories coupled with backward air trajectories, and simple region-tagged chemical transport modeling. Central, south, and west Asia were the major sources of pollutants during the sampling months, with only a small contribution from east Asia. Analysis based on the Weather Research and Forecasting (WRF-STEM) chemical transport model identified a significant contribution (more than 70 %) from south Asia at selected sites. Research into the presence and effect of pollutants in the glaciated areas of Pakistan is economically significant because the surface water resources in the country mainly depend on the rivers (the Indus and its tributaries) that flow from this glaciated area.

Multi-Model Evaluation of Meteorological Drivers, Air Pollutants and Quantification of Emission Sources over the Upper Brahmaputra Basin

“…The WRF-STEM CO tracer and HYSPLIT model classify different geographical regions affecting the air quality over Dibrugarh. The WRF-STEM model used in the present study has already been validated over the complex terrain in Central and Western Himalayan region [75,76]. In contrast to WRF-Chem and WRF-STEM, HYSPLIT is a computationally inexpensive and easily accessible model for identification of concentration pathways.…”

“…Under low RH condition, the significant impact of regional transportation, local emissions, and physicochemical formation jointly dominates the concentration of atmospheric particles [81]. Thus, an increase in the value of RH is favorable for the formation of particles from the liquid-phase, heterogeneous reactions and the hygroscopic growth processes [75]. High T, low wind and RH play a significant role in the enrichment of regional pollution.…”

Reply on RC1

“…In Pakistan, 3 stations (namely Karachi, Mardan, and Hunza) were studied based on the APCC program (Gul et al, 2018).…”

Air Pollution in the Hindu Kush Himalaya

“…South-eastern Tibet receives biomass-burning emissions from Myanmar, Bangladesh, and eastern India (Zhao et al 2013), while the northern parts of the Tibetan Plateau receive dust from the Taklimakan Desert (Huang et al 2007;Cao et al 2009;Xiao et al 2010;Chen et al 2013;Zhao et al 2013;Wang et al 2015). Pollution episodes at Mount Waliguang at the north-eastern corner of the HKH, as well as at Mount Muztagh Ata, in the Pamir range and in the Pakistani Karakoram, have been traced to Central Asia and the Middle East (Wang et al 2006;Che et al 2011;Gul et al 2018). Manora Peak in India receives pollution from the IGP, but also from the Middle East (Dumka et al 2010(Dumka et al , 2015.…”

“…However, the model does give an overall synoptic picture, consistent with the expected behaviour of pollution transport reaching the high glaciers of the HKH. Several research papers using wind back trajectories analysis report that the source of the observed air pollutants reaching the HKH are primarily from the IGP and as far away as Africa (Carrico et al 2003;Bonasoni et al 2012;Ming et al 2009;Babu et al 2011b;Lu et al 2012;Gul et al 2018).…”