Maheswar Rupakheti

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

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±124μg/m(3) and 155±130ng/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 pre-monsoon 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 combustion. The toxic equivalent quantity (TEQ) of particle phase PAHs ranged between 2.74 and 81.5ngTEQ/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 (1ngTEQ/m(3)). This suggests that ambient PAH levels in the Kathmandu Valley pose a serious health risk to its approximately 3.5 million residents.

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario, Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mass with the higher fractions of nitrate and organics. Cleaner northwesterly winds carried aerosols with relatively higher fractions of organics and sulfate. The AMS derived mass size distributions showed that the inorganic species in the particles with vacuum aerodynamic diameters between about 60 nm and 600 nm had mass modal vacuum aerodynamic diameters around 400–500 nm. The particulate organics often exhibited two modes at about 100 nm and 425 nm, more noticeable during fresh pollution events. The small organic mode was well correlated with gas-phase nonmethane hydrocarbons such as ethylbenzene, toluene, and propene, suggesting that the likely sources of small organic particles were combustion related emissions. The particulate nitrate exhibited a diurnal variation with higher concentrations during dark hours and minima in the afternoon. Particulate sulfate and organics showed evidence of photochemical processing with higher levels of sulfate and oxygenated organics in the afternoon. Reasonable agreement among all of the co-located measurements is found, provided the upper size limit of the AMS is considered.

Characterizations of atmospheric particulate-bound mercury in the Kathmandu Valley of Nepal, South Asia

The Kathmandu Valley, located in the Himalayan foothills in Nepal, is heavily polluted. In order to investigate ambient particulate-bound mercury (Hg) in the Kathmandu Valley, a total 64 total suspended particulates (TSP) samples were collected from a sub-urban site in the Kathmandu Valley, the capital region of Nepal during a sampling period of an entire year (April 2013-April 2014). They were analyzed for ambient particulate-bound Hg (PBM) using thermal desorption combined with cold vapor atomic spectroscopy. In our knowledge, it is the first study of ambient PMB in the Kathmandu Valley and the surrounding broader Himalayan foothill region. The average concentration of PBM over the entire sampling period of a year was found to be 850.5 (±962.8) pg m-3 in the Kathmandu Valley. This is comparable to those values reported in the polluted cities of China and significantly higher than those observed in most of urban areas in Asia and other regions of world. The daily average Hg contents in TSP (PBM/TSP) ranges from 269.7 to 7613.0ngg-1 with an average of 2586.0 (±2072.1) ng g-1, indicating the high enrichment of Hg in TSP. The average concentrations of PBM were higher in the winter and pre-monsoon season than in the monsoon and post-monsoon season. The temporal variations in the strength of anthropogenic emission sources combined with other influencing factors, such as ambient temperature and the removal of atmospheric aerosols by wet scavenging are attributable to the seasonal variations of PBM. The considerably high dry deposition flux of PBM estimated by using a theoretical model was 135μgm-2yr-1 at the Kathmandu Valley. This calls for an immediate attention to addressing ambient particulate Hg in the Kathmandu Valley, including considering it as a key component of future air quality monitoring activities and mitigation measures.

Respiratory Effects of High Levels of Particulate Exposure in a Cohort of Traffic Police in Kathmandu, Nepal.

Objectives: To investigate the traffic-related PM2.5 and black carbon (BC) exposures and assess their health effects. Methods: Personal exposure to PM2.5 and BC levels were monitored in a cohort of traffic police (n = 53) at six locations in Kathmandu Valley, Nepal during dry and rainy seasons in 2014. Results: Mean on-road exposure levels of PM2.5 and BC ranged from 34 to 193 &mgr;g/m3 and 12 to 28 &mgr;gC/m3, respectively, and were associated with an acute decline in lung function. Use of N95 mask had clear benefits reducing the lung function decreases after occupational exposures when masks were worn for just half of a workweek. Conclusions: Exposure of high levels of PM2.5 was associated with reduced lung function. Increased levels of BC exposure led to reduced lung function in non-smoking traffic officers with non-normal spirometry observations.

Long-term trends in the total columns of ozone and its precursor gases derived from satellite measurements during 2004–2015 over three different regions in South Asia: Indo-Gangetic Plain, Himalayas and Tibetan Plateau

ABSTRACT Long-term (2004–2015) satellite data over three adjacent yet contrasting regions: Indo-Gangetic Plain, Himalayas and Tibetan Plateau (TP) were used to study the spatiotemporal distribution of total ozone column (TOC) and its precursor gases (such as nitrogen dioxide (NO2), methane (CH4) and carbon monoxide (CO)). The ozone precursor emission data and forest fire points were used to explore the findings. Trace gases showed increasing trend probably due to increasing emission from South Asia as supported by the Emission Database for Global Atmospheric Research emission data. Strong seasonal variation in trace gases was observed with the highest value during the pre-monsoon season, over three regions, possibly due to the biomass burning, pollution build-up and also long-range transport of pollution. TOC exhibited the similar seasonal variation as shown by the earlier ground-based studies over the region. The total column of precursor gases (except methane) exhibited strong seasonality with the highest column during the pre-monsoon season. Patterns in the variations of TOC and related precursors over the Himalayas were similar with that of the TP. Seasonal climatological trends also exhibited increasing pattern except for CO. This work provides an overview on the long-term TOC and its precursor gases which are necessary to understand the regional climate variability especially over the Himalayas and Tibetan Plateau region.

PM Modelling over Nepal with WRF-Chem

Very high particulate matter (PM) and black carbon (BC) concentrations are observed in the Kathmandu Valley, Nepal. With an aim of gaining a better understanding of the dynamics of these air pollutants, PM and BC simulations with the WRF-Chem model have been performed. The comparison of the simulation results with measurements shows that the model strongly underestimated the measured PM and BC levels. It is concluded that this is mainly due to missing up-to-date high resolution information on emissions in the valley.