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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Aug 2018

Research article | 03 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Molecular characterization of organic aerosols in the Kathmandu Valley, Nepal: insights into primary and secondary sources

Xin Wan1,8, Shichang Kang2,7, Maheswar Rupakheti3,4, Qianggong Zhang1,7, Lekhendra Tripathee2, Junming Guo2, Pengfei Chen2, Dipesh Rupakheti2, Arnico K. Panday5, Mark G. Lawrence3, Kimitaka Kawamura6, and Zhiyuan Cong1,7 Xin Wan et al.
  • 1Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China
  • 2State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, CAS, Lanzhou 730000, China
  • 3Institute for Advanced Sustainability Studies (IASS), Potsdam 14467, Germany
  • 4Himalayan Sustainability Institute (HIMSI), Kathmandu, Nepal
  • 5International Centre for Integrated Mountain Development (ICIMOD), Khumaltar, Lalitpur, Nepal
  • 6Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan
  • 7CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
  • 8University of Chinese Academy of Sciences, Beijing 100039, China

Abstract. Organic atmospheric aerosols in the Hindu Kush-Himalayan-Tibetan Plateau region are still poorly characterized. To better understand the sources and formation processes of the primary organic aerosols (POA) and secondary organic aerosol (SOA) in the foothills region of the central Himalaya, we studied atmospheric aerosol samples collected over a one-year period from April 2013 to April 2014 at the suburban site of Bode in the Kathmandu Valley. We measured concentrations of major ions, organic carbon (OC), elemental carbon (EC), and various organic tracers emitted by specific sources. Tracer-based estimation methods were employed to characterize aerosol species, identify their likely sources, and apportion contributions from each source. The concentrations of OC and EC increased during winter with a maximum monthly average in January. Levoglucosan (an organic tracer for biomass burning), OC, and EC showed similar seasonal variations throughout the year. With an annual average concentration of 788±685ngm−3 (ranging from 58.8 to 3079ngm−3), levoglucosan was observed as the dominant species among all the analyzed organic tracers. Biomass burning contributed a significant fraction to OC, averaging 24.9±10.4% during the whole year, and up to 36.3±10.4% in the post-monsoon season. On an annual average basis, anthropogenic toluene-derived secondary OC accounted for 8.8% and biogenic secondary OC contributed 6.2% to total OC. The annual contribution of fugal-spores to OC was 3.2% with the maximum during the monsoon (5.9%). For plant debris, it accounted for 1.4% of OC during the monsoon. Therefore, OC is mainly associated with biomass burning and other anthropogenic activity in the Kathmandu Valley. Our findings are conducive to designing control measures to mitigate the heavy air pollution and its impacts in the Kathmandu Valley and surrounding area.

Xin Wan et al.
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Status: final response (author comments only)
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Xin Wan et al.
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The sources of primary and secondary aerosols in Hindu Kush-Himalayan-Tibetan Plateau region are not well known. Organic molecular tracers are useful for aerosol source apportionment. The characterization of molecular tracers were first systemically investigated and the contribution from primary and secondary sources to carbonaceous aerosols were estimated in the Kathmandu Valley. Our results demonstrate that biomass burning contributed a significant fraction to OC in the Kathmandu Valley.
The sources of primary and secondary aerosols in Hindu Kush-Himalayan-Tibetan Plateau region are...