Quantifying sources, transport, deposition, and radiative forcing of black carbon over the Himalayas and Tibetan Plateau

Abstract

Abstract. Black carbon (BC) particles over the Himalayas and Tibetan Plateau (HTP), both airborne and those deposited on snow, have been shown to affect snowmelt and glacier retreat. Since BC over the HTP may originate from a variety of geographical regions and emission sectors, it is essential to quantify the source–receptor relationships of BC in order to understand the contributions of natural and anthropogenic emissions and provide guidance for potential mitigation actions. In this study, we use the Community Atmosphere Model version 5 (CAM5) with a newly developed source-tagging technique, nudged towards the MERRA meteorological reanalysis, to characterize the fate of BC particles emitted from various geographical regions and sectors. Evaluated against observations over the HTP and surrounding regions, the model simulation shows a good agreement in the seasonal variation in the near-surface airborne BC concentrations, providing confidence to use this modeling framework for characterizing BC source–receptor relationships. Our analysis shows that the relative contributions from different geographical regions and source sectors depend on season and location in the HTP. The largest contribution to annual mean BC burden and surface deposition in the entire HTP region is from biofuel and biomass (BB) emissions in South Asia, followed by fossil fuel (FF) emissions from South Asia, then FF from East Asia. The same roles hold for all the seasonal means except for the summer, when East Asia FF becomes more important. For finer receptor regions of interest, South Asia BB and FF have the largest impact on BC in the Himalayas and central Tibetan Plateau, while East Asia FF and BB contribute the most to the northeast plateau in all seasons and southeast plateau in the summer. Central Asia and Middle East FF emissions have relatively more important contributions to BC reaching the northwest plateau, especially in the summer. Although local emissions only contribute about 10% of BC in the HTP, this contribution is extremely sensitive to local emission changes. Lastly, we show that the annual mean radiative forcing (0.42 W m−2) due to BC in snow outweighs the BC dimming effect (−0.3 W m−2) at the surface over the HTP. We also find strong seasonal and spatial variation with a peak value of 5 W m−2 in the spring over the northwest plateau. Such a large forcing of BC in snow is sufficient to cause earlier snow melting and potentially contribute to the acceleration of glacier retreat.

Chemical characteristics of submicron particles at the central Tibetan Plateau: insights from aerosol mass spectrometry

“…), northern Himalayas, during pre-monsoon was found to be 3-5 times higher than that during the monsoon periods . Since this seasonal variation of aerosol loading is consistent at both the southern and northern Himalayas (C. , aerosol plume was thought to be able to cross the Himalayas, a finding which is also supported by model results (Lu et al, 2012;Lüthi et al, 2015;Zhang et al, 2015). During monsoon period, ambient aerosol from the upwind sources is significantly scavenged during longrange transport and air mass mainly originates from marine area, which can lead to aerosol chemical differences between pre-monsoon and monsoon.…”

Seasonal variation and light absorption property of carbonaceous aerosol in a typical glacier region of the southeastern Tibetan Plateau

“…We use a global aerosol-climate model, the Community Atmosphere Model version 5 (CAM5), equipped with a BC (or EC) source tagging technique (Wang et al, , 2014Zhang et al, 2015) to help estimate the source attribution of BC in the Mt. Yulong area.…”

Transport of regional pollutants through a remote trans-Himalayan valley in Nepal

“…Numerous studies have investigated the transport of pollutants from the IGP to the Himalayan foothills, the immediate source region for potential transport to the Tibetan Plateau (TP) (Pant et al, 2006;Dumka et al, 2008;Komppula et al, 2009;Hyvärinen et al, 2009;Ram et al, 2010;Brun et al, 2011;Gautam et al, 2011;Srivastava et al, 2012). Further, a suite of studies involving satellite imagery (Ramanathan et al, 2007a;Brun et al, 2011), back trajectories (Lu et al, 2011), model calculations (Kopacz et al, 2011;Zhang et al, 2015), ice core analyses (Lee et al, 2008;Kang et al, 2010), and measurements in the higher Himalaya Chen et al, 2017) strongly suggest that pollutants are efficiently transported from the IGP to the higher Himalaya and onto the Tibetan Plateau, especially during spring prior to the monsoon. This transport north of the Himalayas is potentially concerning as the TP plays a vital role in regulating the regional climate due to its effect on the Asian summer monsoon (ASM) and the hydrologic cycle.…”