Temporal variation of atmospheric polycyclic aromatic hydrocarbon concentrations in PM₁₀from the Kathmandu Valley and their gas-particle concentrations in winter

Abstract

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in particulate matter (PM) with a diameter510 mm (PM 10 , 50% cut off) were investigated in the Kathmandu Valley, Nepal, during 2003. In order to understand the dynamics of atmospheric PAHs in winter, the PAH concentrations in total PM and in the gaseous phase were investigated in the valley in December 2005. Total of 45 PAH compounds ( P 45PAHs) were analysed by high-resolution gas chromatography/ high-resolution mass spectrometry (HRGC/HRMS). In 2003, the P 45PAH concentrations in PM 10 ranged between 4.3 and 89 ng m À3 (annual average; 27 AE 24 ng m À3 ). The average concentrations of P 45PAHs in December 2005 were 210 AE 33 ng m À3 in total PM and 430 AE 90 ng m À3 in the gaseous phase. The P 45PAH concentration in PM accounted for more than 30% of the sum of their particulate and gaseous forms. Phenanthrene (Ph) was the most predominant compound in the gaseous phase, whereas four-to seven-ring PAHs were predominant in total PM. The highest values of P 45PAHs occurred in the winter and spring. Estimates of emission sources based on diagnostic molecular ratios showed that atmospheric PAHs in the Kathmandu Valley mainly originated from the exhaust gas of diesel engine. In the winter and spring, PAH pollution would be accelerated by the operations of brick kilns and the frequent formation of an atmospherically stable layer in the valley.

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

“…2), with concentrations being high in the pre-monsoon season, gradually decreasing to minimum concentrations around the mid-monsoon season, and then increasing through the post-monsoon season to maximum concentrations in the early winter. Kishida et al (2009) described a similar seasonal trend in particle phase PAHs (in PM 10 ). Various sources of suspended particles and PAHs exist in the Kathmandu Valley.…”

“…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).…”

“…Daily power cuts can last for 10-18 h. This has resulted in the using of nearly 250,000 small generators, mainly diesel powered, in the Kathmandu Valley alone, causing particulate matter and PAH emissions. Nearly 120 polluting brick kilns, operated from January to April every year, exist in the valley, and low-quality coal is mostly used in these kilns (Kishida et al, 2009;Central Bureau of Statistics, 2006). Furthermore, approximately 700,000 vehicles are in the valley, constituting almost half of the total number of vehicles in the country.…”

“…The valley comprises nearly 3.5 million residents and has a severe air pollution problem (Aryal et al, 2008;Kando et al, 2005;Gurung and Bell, 2013). Only one study examined ambient PAHs in this region, and it reported extremely high total PAH concentrations (640 ng/m 3 ) in Kathmandu in winter (Kishida et al, 2009). The present study presents results of year-long measurement of 15 priority particle phase PAHs in the Kathmandu Valley.…”

Characteristics of Particulate-Phase Polycyclic Aromatic Hydrocarbons (PAHs) in the Atmosphere over the Central Himalayas

“…However, current knowledge of PAH compositions for this region remains deficient (Kishida et al, 2009;Rajput et al, 2013;Chen et al, 2015bChen et al, , 2016, especially in terms of spatial and seasonal variations. Here, we present results of a year-long time series of TSP and particulate-phase PAHs observations at six sites (Lumbini, Pokhara, Jomsom, Zhongba, Dhunche and Nyalam) across two Himalayan transects to investigate characteristics of PAHs in this critical region (Fig.…”