Abstract
Abstract. High temporal resolution measurements of black carbon (BC) and organic carbon (OC) covering the time period of 1956–2006 in an ice core over the southeastern Tibetan Plateau show a distinct seasonal dependence of BC and OC with higher respective concentrations but a lower OC / BC ratio in the non-monsoon season than during the summer monsoon. We use a global aerosol-climate model, in which BC emitted from different source regions can be explicitly tracked, to quantify BC source–receptor relationships between four Asian source regions and the southeastern Tibetan Plateau as a receptor. The model results show that South Asia has the largest contribution to the present-day (1996–2005) mean BC deposition at the ice-core drilling site during the non-monsoon season (October to May) (81%) and all year round (74%), followed by East Asia (14% to the non-monsoon mean and 21% to the annual mean). The ice-core record also indicates stable and relatively low BC and OC deposition fluxes from the late 1950s to 1980, followed by an overall increase to recent years. This trend is consistent with the BC and OC emission inventories and the fuel consumption of South Asia (as the primary contributor to annual mean BC deposition). Moreover, the increasing trend of the OC / BC ratio since the early 1990s indicates a growing contribution of coal combustion and/or biomass burning to the emissions. The estimated radiative forcing induced by BC and OC impurities in snow has increased since 1980, suggesting an increasing potential influence of carbonaceous aerosols on the Tibetan glacier melting and the availability of water resources in the surrounding regions. Our study indicates that more attention to OC is merited because of its non-negligible light absorption and the recent rapid increases evident in the ice-core record.
Highlights
Carbonaceous aerosol, released from fossil fuel, biofuel and/or biomass combustion, contains both black carbon (BC, a.k.a. elemental carbon, EC), a strong light absorber, and organic carbon (OC), which absorbs the near infrared, but more weakly than BC (Kirchstetter et al, 2004; Bond and Bergstrom, 2006)
During the cold and dry winter season, haze builds up over South Asia, and exerts profound influences on regional radiative forcing (Ramanathan et al, 2007; Ramanathan and Carmichael, 2008), hydrologic cycles (Menon et al, 2002; Ramanathan et al, 2005), and likely Himalaya–Tibetan glacier melting that could be accelerated by the absorption of sunlight induced by BC in the air and deposited on the ice and snow surfaces (Ramanathan et al, 2007; Hansen and Nazarenko, 2004), BC deposited in snow and glaciers at some locations may not significantly affect the energy balance (Ming et al, 2013; Kaspari et al, 2014)
The seasonal dependence of BC and OC in ice cores is consistent with available observations of atmospheric aerosols on the southern slope of the Himalayas and the southeastern Tibetan Plateau, where the high concentration of carbonaceous aerosols during the cold and dry season suggested an association with the South Asian haze
Summary
Carbonaceous aerosol, released from fossil fuel, biofuel and/or biomass combustion, contains both black carbon (BC, a.k.a. elemental carbon, EC), a strong light absorber, and organic carbon (OC), which absorbs the near infrared, but more weakly than BC (Kirchstetter et al, 2004; Bond and Bergstrom, 2006). M. Wang et al.: Carbonaceous aerosols recorded in a southeastern Tibetan glacier be the second strongest climate warming forcing agent after carbon dioxide (Jacobson, 2001; IPCC, 2013). Wang et al.: Carbonaceous aerosols recorded in a southeastern Tibetan glacier be the second strongest climate warming forcing agent after carbon dioxide (Jacobson, 2001; IPCC, 2013) Because of their high population density and relatively low combustion efficiency, developing countries in South and East Asia such as India and China are hotspots of carbonaceous aerosol emissions (Ramanathan and Carmichael, 2008). During the cold and dry winter season, haze (heavily loaded with carbonaceous aerosols) builds up over South Asia, and exerts profound influences on regional radiative forcing (Ramanathan et al, 2007; Ramanathan and Carmichael, 2008), hydrologic cycles (Menon et al, 2002; Ramanathan et al, 2005), and likely Himalaya–Tibetan glacier melting that could be accelerated by the absorption of sunlight induced by BC in the air and deposited on the ice and snow surfaces (Ramanathan et al, 2007; Hansen and Nazarenko, 2004), BC deposited in snow and glaciers at some locations may not significantly affect the energy balance (Ming et al, 2013; Kaspari et al, 2014)
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