Abstract
Abstract. The Himalayas and the Tibetan Plateau region (HTP), despite being a remote and sparsely populated area, is regularly exposed to polluted air masses with significant amounts of aerosols including black carbon. These dark, light-absorbing particles are known to exert a great melting potential on mountain cryospheric reservoirs through albedo reduction and radiative forcing. This study combines ground-based and satellite remote sensing data to identify a severe aerosol pollution episode observed simultaneously in central Tibet and on the southern side of the Himalayas during 13–19 March 2009 (pre-monsoon). Trajectory calculations based on the high-resolution numerical weather prediction model COSMO are used to locate the source regions and study the mechanisms of pollution transport in the complex topography of the HTP. We detail how polluted air masses from an atmospheric brown cloud (ABC) over South Asia reach the Tibetan Plateau within a few days. Lifting and advection of polluted air masses over the great mountain range is enabled by a combination of synoptic-scale and local meteorological processes. During the days prior to the event, winds over the Indo-Gangetic Plain (IGP) are generally weak at lower levels, allowing for accumulation of pollutants and thus the formation of ABCs. The subsequent passing of synoptic-scale troughs leads to southwesterly flow in the middle troposphere over northern and central India, carrying the polluted air masses across the Himalayas. As the IGP is known to be a hotspot of ABCs, the cross-Himalayan transport of polluted air masses may have serious implications for the cryosphere in the HTP and impact climate on regional to global scales. Since the current study focuses on one particularly strong pollution episode, quantifying the frequency and magnitude of similar events in a climatological study is required to assess the total impact.
Highlights
The Himalayas and Tibetan Plateau region (HTP), sometimes called the “third pole”, contains the largest volume of ice outside the polar regions and impacts radiative budgets and climate (Ye and Wu, 1998; Ma et al, 2009)
The goals of this study are (1) to investigate whether major pollution episodes identified on the TP set in synchronously with pollution episodes measured at the southern face of the Himalayas, (2) to determine if “plumes” of air pollution observed on the TP originate at the southern side of the Himalayas, (3) to determine whether atmospheric brown cloud (ABC) measured at the southern side of the Himalayas can traverse the high mountain range through the major north– south river valleys and by being lifted and advected over the Greater Himalayas and (4) to understand which local and synoptic-scale meteorological phenomena enable the transport across the Himalayas
This episode has been identified by analyzing Aerosol Robotic Network (AERONET) time series and comparing them to black carbon (BC) observational data from sites in the HTP (Sect. 3.1.1) and to Ozone Monitoring Instrument (OMI) absorbing aerosol optical depth (AAOD) data in the Indo-Gangetic Plain (IGP) (Sect. 3.1.2), which allows the assessment of the ABC extension
Summary
The Himalayas and Tibetan Plateau region (HTP), sometimes called the “third pole”, contains the largest volume of ice outside the polar regions and impacts radiative budgets and climate (Ye and Wu, 1998; Ma et al, 2009). In addition to greenhouse gases, increasing ambient concentrations of black carbon (BC) appear to be an anthropogenic driving force of the observed changes in these remote regions (Lau et al, 2010; Ramanathan and Carmichael, 2008). Lightabsorbing aerosol particles such as mineral dust and BC con-. Lüthi et al.: Atmospheric brown clouds reach the Tibetan Plateau by crossing the Himalayas tribute to the atmospheric heating and the albedo reduction once deposited on glaciers. Albeit only contributing a few percent to the total aerosol mass, BC exerts major radiative effects (Bond et al, 2013; Jacobson, 2001), especially over the HTP during pre-monsoon seasons when the solar radiative flux at the surface is very high (Flanner et al, 2007)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
