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.

• High concentrations of 4-6 ring PAHs were reported in the atmosphere of Kathmandu.• PAH concentrations in non-monsoon season were higher than those in monsoon season.• PAH ratios indicated that diesel and biomass fuels were main emission sources.• Toxic equivalent concentration of PAHs was 26 times higher than the WHO guideline. The Kathmandu Valley in the foothills of the Himalayas, where the capital city of Nepal is located, has one of the most serious air pollution problems in the world. In this study, total suspended particle (TSP) samples collected over a year (April 2013-March 2014 in the Kathmandu Valley were analyzed for determining the concentrations of 15 priority particle-bound polycyclic aromatic hydrocarbons (PAHs). The TSP and PAH concentrations were extremely high, with annual average concentration being 199 ± 124 μg/m 3 and 155 ± 130 ng/m 3 , respectively, which are comparable to those observed in Asian cities such as Beijing and Delhi. The TSP and PAH concentrations varied considerably, with the seasonal average concentration being maximal during the post-monsoon season followed by, in descending order, the winter, pre-monsoon, and monsoon seasons. In the winter and premonsoon seasons, ambient TSP and PAH concentrations increased because of emissions from brick kilns and the use of numerous small generators. Moreover, in the pre-monsoon season, forest fires in the surrounding regions influenced the TSP and PAH concentrations in the valley. PAHs with 4 to 6 rings constituted a predominant proportion (92.3-93.3%) of the total PAHs throughout the year. Evaluation of diagnostic molecular ratios indicated that the atmospheric PAHs in the Kathmandu Valley originated mainly from diesel and biomass G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v combustion. The toxic equivalent quantity (TEQ) of particle phase PAHs ranged between 2.74 and 81.5 ng TEQ/ m 3 , which is considerably higher than those reported in other South Asian cities, and 2-80 times higher than the World Health Organization guideline (1 ng TEQ/m 3 ). This suggests that ambient PAH levels in the Kathmandu Valley pose a serious health risk to its approximately 3.5 million residents.

Twenty snow samples were collected from the Qiyi glacier in Qilian Mountains, the Yuzhufeng glacier in eastern Kunlun Mountains, the Xiaodongkemadi glacier in Tanggula Mountains, and the Gurenhekou glacier in Nyainqêntanglha Range over the Tibetan Plateau. The concentration and distribution features of sixteen priority Polycyclic Aromatic Hydrocarbons (PAHs) were determined by gas chromatography equipped with a mass spectrometry detector (GC-MS). The sources of these PAHs were explored as well. Our results indicated that the average concentrations of PAHs in snow were in the range of 20.45−60.57 ng/L. Maximum PAHs levels were found in the YZF glacier and minimum in the XDKMD glacier. However, no apparent regional distribution pattern of PAHs was found in the glaciers over the Tibetan Plateau. Moreover, the 2−4 ring low molecular weight PAHs predominated in snow samples and the concentrations of phenanthrene was the highest. Integrated factor analysis and isomer pair ratios suggested that PAHs of glaciers over the Tibetan Plateau were derived from low temperature combustion of coal and biomass, and partially from the exhaust gas of locomotives. Air mass back trajectory indicated that organic compounds detected in snowpit of these four glaciers, in the period of time they represented, mainly came from Central Asia and the arid area of Northwest China by westerly wind circulation.Tibetan Plateau, snow, polycyclic aromatic hydrocarbon, substance origin Citation:Li Q L, Wang N L, Wu X B, et al. Sources and distribution of polycyclic aromatic hydrocarbons of different glaciers over the Tibetan Plateau. Sci

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PAH concentrations were measured in total suspended particle (TSP) samples collected from six sites along two southnorth transects across the central Himalayas from April 2013 to March 2014. The annual average TSP and PAH (especially 5-and 6-ring compounds) concentrations were found to decrease noticeably northwards along both transects. At rural and urban sites, the TSP and PAH concentrations showed clear seasonal variations, with the lower concentrations around the mid-monsoon season and the higher values in the winter season. Meanwhile, at the remote sites (e.g., Nyalam and Zhongba), these pollutants generally remained constant throughout the year but with relatively higher levels during the pre-monsoon season. Both IndP/(IndP + BghiP) and Fla/(Fla + Pyr) ratios suggested that atmospheric PAHs from urban and rural sites were mainly associated with emissions from biomass burning, coal burning and petroleum combustion. However, the contribution of biomass burning increased at remote sites. Similar compositions of PAHs were found at three remote sites located on both sides of the Himalayas (Jomsom, Zhongba, and Nyalam), suggesting that the northern side of the Himalayas may be affected by anthropogenic emissions from the Indo-Gangetic Plain (IGP) via long-range atmospheric transport. This work provides a database of PAHs in central Himalayas for further assessing environmental risk of air pollution in the remote regions.

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