Abstract
Abstract. Organic atmospheric aerosols in the Hindu Kush–Himalayas–Tibetan Plateau region are still poorly characterized. To better understand the chemical characteristics and sources of organic aerosols in the foothill region of the central Himalaya, the atmospheric aerosol samples were collected in Bode, a suburban site of the Kathmandu Valley (KV) over a 1-year period from April 2013 to April 2014. Various molecular tracers from specific sources of primary organic aerosols (POAs) and secondary organic aerosols (SOAs) were determined. Tracer-based estimation methods were employed to apportion contributions from each source. The concentrations of organic carbon (OC) and elemental carbon (EC) increased during winter with a maximum monthly average in January. Levoglucosan (a molecular tracer for biomass burning, BB) was observed as the dominant species among all the analyzed organic tracers and its annual average concentration was 788±685 ng m−3 (ranging from 58.8 to 3079 ng m−3). Isoprene-SOA (I-SOA) represented a high concentration among biogenic-SOA tracers. For the seasonality, anhydrosugars, phenolic compounds, resin acid, and aromatic SOA tracer showed similar seasonal variations with OC and EC while monosaccharides, sugar alcohols, and I-SOA tracers showed lower levels during winter. BB 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 fungal spores to OC was 3.2 % with a maximum during the monsoon season (5.9 %). For plant debris, it accounted for 1.4 % of OC during the monsoon. Therefore, OC is mainly associated with BB and other anthropogenic activity in the KV. Our findings are conducive to designing effective measures to mitigate the heavy air pollution and its impacts in the KV and surrounding area.
Highlights
South Asia, especially the Indo-Gangetic Plain (IGP) region, is a global air pollution hotspot
It generally corresponded to the buildup of the atmospheric brown clouds (ABCs), which engulfed most of South Asia and the northern Indian Ocean extending from November to May (Ramanathan et al, 2005)
Field measurements of atmospheric aerosols were conducted in a semi-urban site (Bode) of the Kathmandu Valley (KV), Nepal, from April 2013 to April 2014
Summary
South Asia, especially the Indo-Gangetic Plain (IGP) region, is a global air pollution hotspot. Wan et al.: Molecular characterization of organic aerosols in the Kathmandu Valley ing recent decades (Ramanathan et al, 2005; Muzzini and Aparicio, 2013; Lawrence and Lelieveld, 2010) While these pollutants are of concern locally near the emission sources, they can in a short span of time, be transported to rural and remote regions over a long distance. Types, levels, atmospheric transport and transformation, impacts, and mitigation of various atmospheric pollutants were not well characterized in the vast mountain areas and the foothill region in South Asia In this context, the international project of “A Sustainable Atmosphere for the Kathmandu Valley (SusKat)” was launched, aiming to comprehensively understand the causes of the severe air pollution in the region, and identifying appropriate solutions to reduce its impacts (Rupakheti et al, 2019). This paper presents analyses of samples collected as part of the SusKat field campaign
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
