Characteristics and Sources of Carbonaceous, Ionic, and Isotopic Species of Wintertime Atmospheric Aerosols in Kathmandu Valley, Nepal

Abstract

To investigate the air pollution from aerosols in Kathmandu during winter, bulk aerosol samples were collected during winter [2007][2008] to characterize carbonaceous and ionic species and carbon and nitrogen isotopes. This study illustrates the applications of carbon and nitrogen isotope data for characterizing aerosols and their implications for identifying sources that were inconsistent with the results for the carbonaceous and ionic aerosols. Mean concentrations of organic carbon (OC), elemental carbon (EC), and water soluble organic carbon (WSOC) in Kathmandu during the period were 20.02 ± 6.59 (1σ), 4.48 ± 1.17, and 10.09 ± 3.64 µgC/m 3 , respectively. Elemental carbon and OC were correlated (R 2 = 0.56), likely indicating common sources for both species, as well as for the precursors that led to the formation of secondary organic carbon (SOC). The mean estimated SOC contribution to OC was 31%, suggesting that local emission is more important than transport and processing during winter in Kathmandu. On average, 50% of the OC was water soluble, and the correlation of SOC with WSOC (R 2 = 0.66) suggests that the majority of SOC and some primary organic carbon (POC) were water soluble in Kathmandu. The mean δ 13 C of -25.74 ± 0.19‰ observed in aerosols of Kathmandu confirms consistent anthropogenic sources such as fossil fuel combustion. Heavier carbon also was observed to be associated with the water-soluble fraction of OC in aerosols. The mean δ 15 N of 9.45 ± 0.87‰ suggests the limited influence of biomass burning and its strong correlation with crustal cations Ca 2+ (R 2 = 0.74, p < 0.05) and Mg 2+ (R 2 = 0.71, p < 0.05) indicates distant sources. Principal component analysis revealed four major sources/pathways for particles: local and vehicular emissions, secondary gas-to-particle conversion, aqueous processing, and dust transport, each explaining ~39, 23, 11, and 9% of the variance.

Characteristics and sources of polycyclic aromatic hydrocarbons in atmospheric aerosols in the Kathmandu Valley, Nepal

“…Previous studies on particulate chemical composition, including carbonaceous aerosols, ions/ metals, and PAHs, have suggested that the atmospheric composition in the Kathmandu Valley is considerably influenced by anthropogenic emissions from sources such as vehicles, industries, and biomass burning, and even the long-range transportation of pollutants from the Indian subcontinent (Kishida et al, 2009;Shakya et al, 2010;Tripathee et al, 2014).…”

“…C values of aerosols in Kathmandu have also indicated that local vehicular emissions were a major source of pollutants (Shakya et al, 2010). In addition, PM 10 emissions from vehicular activities and industrial sources in Kathmandu constituted approximately 62% and 17% of the total PM 10 emissions, respectively (ICIMOD, 2007).…”

Near-road sampling of PM&lt;sub&gt;2. 5&lt;/sub&gt;, BC, and fine-particle chemical components in Kathmandu Valley, Nepal

“…Limited information exists for PM 2.5 (particles smaller than 2.5 µm in diameter) pollution (Aryal et al, 2009;Gurung and Bell, 2012; in this location, and even less information is available for PM chemical composition in the valley (Shakya et al, 2010;Chen et al, 2015). As developing nations continue to grow economically and societally, they are likely to be faced with critical decisions on energy consumption, transportation infrastructure, and public health protection measures.…”

“…In addition to emissions from vehicles and resuspended road dust due to vehicles, emissions from more than 100 brick kilns, the widespread use of small captive power generators during scheduled power cuts, and burning household and/or municipal wastes are other major sources of air pollution in the valley (ICIMOD, 2007;Shakya et al, 2010;The World Bank, 2014;Kim et al, 2015). The Kathmandu Valley has been facing rapidly deteriorating air quality on a metropolitan scale resulting from rapid urbanization and modernization, high population growth, the increasing number of vehicles, and increasing fuel consumption throughout the region.…”

Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain

“…Among the major sources of aerosol, emissions from agricultural-waste and biomass burning dominate during the wintertime (Dec-Feb) (Venkataraman et al, 2005;Rengarajan et al, 2007;Gustafsson et al, 2009;Ram et al, 2010a;Shakya et al, 2010;Rajput et al, 2011;Ram and Sarin, 2011). The transport of mineral aerosol from arid and semiarid regions of western India, during the summer (Aprilearly June), imparts strong temporal variability in the chemical composition and optical properties of aerosol (Jethva et al, 2005;Chinnam et al, 2006).…”