Abstract
Abstract. The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004–2006 and the ice core drillings of BC deposition during 1986–1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991–1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3–4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the “normal period” (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m−2, while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m−2. During the Kuwait fires period, the RFI values increased about 2–5 times higher than in the “normal period”, suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region.
Highlights
Black carbon (BC) particles emitted from combustion are considered an important air pollutant, as they have a direct effect by absorbing and scattering solar radiation, and an indirect effect by the change in cloud microphysical processes and the efficiency of precipitation (Ramanathan et al, 2001)
Bisiaux et al (2012) analyzed two ice cores drilled in Antarctica and found that the ice core records of BC deposition reflected the change in atmospheric BC emission, distribution and transport in the Southern Hemisphere
Because the measured site is located in a “clean” region of BC emission, the BC particles were mostly transported from a long distance of the upwind regions
Summary
Black carbon (BC) particles emitted from combustion are considered an important air pollutant, as they have a direct effect by absorbing and scattering solar radiation, and an indirect effect by the change in cloud microphysical processes (acting as ice nuclei) and the efficiency of precipitation (acting as cloud condensation nuclei) (Ramanathan et al, 2001). Albedo changes induced by a strongly light-absorbing component deposited on the surface of snow and ice are key parameters in governing the radiative forcing and accelerate melting (Holben et al, 1998; Hansen and Nazarenko, 2004) These important properties make BC a key topic related to climate change, but are not well understood due to the very different inhomogeneous spatial and temporal distributions of BC, especially in remote areas such as the Tibetan Plateau. By using an ice core in Greenland, the BC emissions from industrial activities and forest fires are differentiated (McConnell et al, 2007) These studies indicate that BC records in history are an important and practicable method to investigate the regional aerosol transport and emission variations
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