Wintertime Air Quality across the Kathmandu Valley, Nepal: Concentration, Composition, and Sources of Fine and Coarse Particulate Matter.

The Kathmandu Valley in Nepal experiences poor air quality, especially in the dry winter season. In this study, we investigated the concentration, chemical composition, and sources of fine and coarse particulate matter (PM2.5, PM10, and PM10-2.5) at three sites within or near the Kathmandu Valley during the winter of 2018 as part of the second Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE 2). Daily PM2.5 concentrations were very high throughout the study period, ranging 72-149 µg m-3 at the urban Ratnapark site in Kathmandu, 88-161 µg m-3 at the suburban Lalitpur site, and 40-74 µg m-3 at rural Dhulikhel on the eastern rim of the Kathmandu Valley. Meanwhile, PM10 ranged 194-309, 174-377, and 64-131 µg m-3, respectively. At the Ratnapark site, crustal materials from resuspended soil contributed an average of 11% of PM2.5 and 34% of PM10. PM2.5 was largely comprised of organic carbon (OC, 28-30% by mass) and elemental carbon (EC, 10-14% by mass). As determined by chemical mass balance source apportionment modeling, major PM2.5 OC sources were garbage burning (15-21%), biomass burning (10-17%), and fossil fuel (14-26%). Secondary organic aerosol (SOA) contributions from aromatic volatile organic compounds (13-23% OC) were larger than those from isoprene (0.3-0.5%), monoterpenes (0.9-1.4%), and sesquiterpenes (3.6-4.4%). Nitro-monoaromatic compounds-of interest due to their light-absorbing properties and toxicity-indicate the presence of biomass burning-derived SOA. Knowledge of primary and secondary PM sources can facilitate air quality management in this region.

Particulate Matter and Risk of Hospital Admission in the Kathmandu Valley, Nepal: A Case-Crossover Study.

Air pollution is known to lead to a substantial health burden, but the majority of evidence is based on data from North America and Europe. Despite rising pollution levels, very limited information is available for South Asia. We investigated the impact of particulate matter with an aerodynamic diameter less than or equal to 10 µm (PM10) on hospitalization, by cause and subpopulation, in the Kathmandu Valley, an understudied and rapidly urbanizing region in Nepal. Individual-level daily inpatient hospitalization data (2004-2007) were collected from each of 6 major hospitals, as Nepal has no central data collection system. Time-stratified case-crossover analysis was used with interaction terms for potential effect modifiers (e.g., age, sex, and socioeconomic status), with adjustment for day of the week and weather. Daily PM10 concentrations averaged 120 µg/m3, with the daily maximum reaching 403 µg/m3. A 10-µg/m3 increase in PM10 level was associated with increased risks of hospitalization of 1.00% (95% confidence interval (CI): 0.62, 1.38), 1.70% (95% CI: 0.18, 3.25), and 2.29% (95% CI: 0.18, 4.43) for total, respiratory, and cardiovascular admissions, respectively. We did not find strong evidence of effect modification by age, sex, or socioeconomic status. These results, in combination with the high levels of exposure, indicate a potentially serious human health burden from air pollution in the Kathmandu Valley.

Modeling the intraurban variation in nitrogen dioxide in urban areas in Kathmandu Valley, Nepal.

BACKGROUND: With growing urbanization, traffic has become one of the main sources of air pollution in Nepal. Understanding the impact of air pollution on health requires estimation of exposure. Land use regression (LUR) modeling is widely used to investigate intraurban variation in air pollution for Western cities, but LUR models are relatively scarce in developing countries. In this study, we developed LUR models to characterize intraurban variation of nitrogen dioxide (NO2) in urban areas of Kathmandu Valley, Nepal, one of the fastest urbanizing areas in South Asia. METHODS: Over the study area, 135 monitoring sites were selected using stratified random sampling based on building density and road density along with purposeful sampling. In 2014, four sampling campaigns were performed, one per season, for two weeks each. NO2 was measured using duplicate Palmes tubes at 135 sites, with additional information on nitric oxide (NO), NO2, and nitrogen oxide (NOx) concentrations derived from Ogawa badges at 28 sites. Geographical variables (e.g., road network, land use, built area) were used as predictor variables in LUR modeling, considering buffers 25-400m around each monitoring site. RESULTS: Annual average NO2 by site ranged from 5.7 to 120ppb for the study area, with higher concentrations in the Village Development Committees (VDCs) of Kathmandu and Lalitpur than in Kirtipur, Thimi, and Bhaktapur, and with variability present within each VDC. In the final LUR model, length of major road, built area, and industrial area were positively associated with NO2 concentration while normalized difference vegetation index (NDVI) was negatively associated with NO2 concentration (R2=0.51). Cross-validation of the results confirmed the reliability of the model. CONCLUSIONS: The combination of passive NO2 sampling and LUR modeling techniques allowed for characterization of nitrogen dioxide patterns in a developing country setting, demonstrating spatial variability and high pollution levels.

The state of scientific evidence on air pollution and human health in Nepal.

Air pollution has been linked to acute and chronic health effects. However, the majority of evidence is based in North America and Europe, with a growing number of studies in Asia and Latin America. Nepal is one of the many South Asian countries where little such research has been conducted. We summarized the state of scientific evidence and identify research gaps based on the existing literature on air pollution and human health in Nepal. We performed a systematic literature search to identify relevant studies. Studies were categorized as those that estimate: (1) health impacts of indoor air pollution, (2) health impacts of outdoor air pollution, (3) health burdens from outdoor air pollution in Nepal based on existing concentration-response relationships from elsewhere, or (4) exposure and air quality but do not link to health. We identified 89 studies, of which 23 linked air pollution to health impacts. The remainder focused on exposure and air quality, demonstrating high pollution levels. The few health studies focused mainly on indoor air (n=15), especially in rural areas and during cooking. Direct exposure measurements were for short time periods; most studies used indirect exposure methods (e.g., questionnaire). Most health studies had small sample sizes with almost all focusing on respiratory health. Although few studies have examined air pollution and health in Nepal, the existing studies indicate high pollution levels and suggest large health impacts. Nepal's dearth of scientific research on air pollution and health is not unique and likely is similar to that of many other developing regions. Future research with larger studies and more health outcomes is needed. Key challenges include data availability.

Exposure to airborne particulate matter in Kathmandu Valley, Nepal.

Kathmandu Valley, Nepal, has severe air pollution, although few studies examine air pollution and health in this region. To the best of our knowledge, no previous studies in Nepal used time-activity diaries or conducted personal monitoring of individuals' exposures. We investigated personal exposure of particulate matter (PM) with aerodynamic diameter ≤2.5 µm (PM(2.5)) by location, occupation, and proximity to roadways. PM(2.5) monitoring, time-activity diary, respiratory health questionnaire, and spirometer testing were performed from 28 June 2009 to 7 August 2009 for 36 subjects, including traffic police (TP), indoor officer workers next to main road (IOWs_NMR) and away from main road (IOWs_AMR), in urban area (UA), urban residential area, and semi-UA (SUA). TP had the highest exposure of all the occupations (average 51.2 µg/m(3), hourly maximum >500 µg/m(3)). TP levels were higher at the UA than other locations. IOW_NMR levels (averaged 46.9 µg/m(3)) were higher than those of IOW_AMR (26.2 µg/m(3)). Exposure was generally higher during morning rush hours (0800-1100 hours) than evening rush hours (1500-1800 hours) for all occupations and areas (78% of days for TP and 84% for urban IOW). PM(2.5) personal exposures for each occupation at each location exceeded the World Health Organization ambient PM(2.5) guideline (25 µg/m(3)). Findings suggest potential substantial health impacts of air pollution on this region, especially for TP.