Articles | Volume 17, issue 14
Atmos. Chem. Phys., 17, 8867–8885, 2017

Special issue: Atmospheric pollution in the Himalayan foothills: The SusKat-ABC...

Atmos. Chem. Phys., 17, 8867–8885, 2017

Research article 21 Jul 2017

Research article | 21 Jul 2017

Organic molecular tracers in the atmospheric aerosols from Lumbini, Nepal, in the northern Indo-Gangetic Plain: influence of biomass burning

Xin Wan1,9, Shichang Kang2,8,9, Quanlian Li2, Dipesh Rupakheti1,9, Qianggong Zhang1,8, Junming Guo1,9, Pengfei Chen2, Lekhendra Tripathee2, Maheswar Rupakheti3,4, Arnico K. Panday5, Wu Wang6, Kimitaka Kawamura7, Shaopeng Gao1, Guangming Wu1,9, and Zhiyuan Cong1,8 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), Kathmandu, Nepal
  • 6School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, China
  • 7Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan
  • 8CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100085, China
  • 9University of Chinese Academy of Sciences, Beijing 100039, China

Abstract. To better understand the characteristics of biomass burning in the northern Indo-Gangetic Plain (IGP), total suspended particles were collected in a rural site, Lumbini, Nepal, during April 2013 to March 2014 and analyzed for the biomass burning tracers (i.e., levoglucosan, mannosan, vanillic acid). The annual average concentration of levoglucosan was 734 ± 1043 ng m−3 with the maximum seasonal mean concentration during post-monsoon season (2206 ± 1753 ng m−3), followed by winter (1161 ± 1347 ng m−3), pre-monsoon (771 ± 524 ng m−3) and minimum concentration during monsoon season (212 ± 279 ng m−3). The other biomass burning tracers (mannosan, galactosan, p-hydroxybenzoic acid, vanillic acid, syringic acid and dehydroabietic acid) also showed the similar seasonal variations. There were good correlations among levoglucosan, organic carbon (OC) and elemental carbon (EC), indicating significant impact of biomass burning activities on carbonaceous aerosol loading throughout the year in Lumbini area. According to the characteristic ratios, levoglucosan ∕ mannosan (lev ∕ man) and syringic acid ∕ vanillic acid (syr ∕ van), we deduced that the high abundances of biomass burning products during non-monsoon seasons were mainly caused by the burning of crop residues and hardwood while the softwood had less contribution. Based on the diagnostic tracer ratio (i.e., lev ∕ OC), the OC derived from biomass burning constituted large fraction of total OC, especially during post-monsoon season. By analyzing the MODIS fire spot product and 5-day air-mass back trajectories, we further demonstrated that organic aerosol composition was not only related to the local agricultural activities and residential biomass usage but also impacted by the regional emissions. During the post-monsoon season, the emissions from rice residue burning in western India and eastern Pakistan could impact particulate air pollution in Lumbini and surrounding regions in southern Nepal. Therefore, our finding is meaningful and has a great importance for adopting the appropriate mitigation measures, not only at the local level but also by involving different regions and nations, to reduce the biomass burning emissions in the broader IGP region nations.

Short summary
Biomass burning (BB) tracers in the aerosols in Lumbini, northern IGP, were studied for the first time. The levoglucosan was the predominant tracer and BB significantly contributed to the air quality in Lumbini. Mixed crop residues and hardwood were main burning materials. BB emissions constituted large fraction of OC, especially during the post-monsoon season. The sources of BB aerosols in Lumbini varies seasonally due to the influence of local emissions and long-range transport.
Final-revised paper