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

Abstract

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 postmonsoon 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 nonmonsoon 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 airmass 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.

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

“…Table 1 summarizes with the lowest concentrations in the monsoon season (1.34± 0.90 µg m −3 ) and the highest concentrations in the postmonsoon season (OC: 2.57 ± 1.30 µg m −3 ). Similar seasonal differences were also found in other areas such as Lumbini, Nepal (Wan et al, 2017); Nepal Climate Observatory -Pyramid (NCO-P) (Bonasoni et al, 2010); Kanpur, India (Ram et al, 2012); and Delhi, India (Mandal et al, 2014). Moreover, monthly averaged EC and OC concentrations were analyzed for Mt.…”

“…The annual mean OC / EC ratio in samples from the GHZ basin was 2.90 ± 1.80, while the monsoon season had the highest value (4.40 ± 2.00) and the winter season had the lowest value (1.93 ± 1.58) ( Table 2). Previous studies suggested that OC / EC ratios from biofuel and biomass burning emissions are generally higher than those from fossil fuel combustion Ram et al, 2012;Cong et al, 2015b;Wan et al, 2017). Strong photochemical reactions (due to extensive solar radiation) (Fig.…”

“…4 and 5) when wet removal by precipitation is inefficient. This suggests the importance of seasonal changes in sources (Carrico et al, 2003;Cong et al, 2015b;Wan et al, 2017). In addition, the OC / EC ratio was usually employed to evaluate the combustion fuel sources.…”

“…Yulong. Agra and Lumbini have been identified as regions in the world that are highly affected by biomass burning (Wan et al, 2017). A large amount of car- Lüthi et al, 2014), which substantially influence the Mt.…”

Chemical characterization of long-range transport biomass burning emissions to the Himalayas: insights from high-resolution aerosol mass spectrometry

“…However, the chemical properties of aerosol particles are still not well understood in the Himalayas region due to its remote and harsh environments, challenging weather conditions, and logistical difficulties. In addition, most available studies are based mainly on off-line filter sampling of ambient aerosol or snow/ice samples followed by laboratory analyses Ram et al, 2010;Li et al, 2016;Wan et al, 2017). These studies have usually had a relatively low temporal resolution (days to weeks); therefore, real-time consecutive field measurement, especially focusing on the high-resolution size-resolved chemical characteristics of aerosol particles, is of great importance and necessary to give insight into the sources and the dynamic chemical evolution of ambient aerosol.…”