The overall goals of this collaborative research project were (1) to measure emissions of gaseous and particulate pollutants from major combustion sources in Nepal (including cooking fires, garbage burning, brick kilns, and vehicles) and (2) to evaluate associated impacts on regional air quality, climate, and health.  As part of the larger effort, the University of Virginia investigated three interrelated issues.

(1)  Concentrations of black carbon (BC) and ozone (O₃) and related meteorological conditions were measured continuously within the Kali Gandaki Valley, a deep, trans-Himalayan valley in Nepal.  Differential heating of the valley floor sustained high-velocity, up valley winds during daytime relative to low-velocity, down valley winds at night.  This alternative wind regime resulted in significant net up-valley transport of pollutants. These results support the hypothesis that deep Himalayan valleys are important conduits by which combustion products emitted over the Indo-Gangetic Plain of southern Asia are transported to the high Himalaya and the Tibetan plateau.

(2) Influences of the subtropical westerly jet (SWJ) in modulating tropospheric O₃ over the Himalaya were investigated using vertical profiles of O₃, relative humidity (RH), potential temperature, and wind speed measured with balloon-born instruments in conjunction with model calculations. During winter, the Tibetan plateau creates a strong thermal gradient that contours the plateau.  The varying location of the SWJ with respect to the thermal gradient along the southern slope of the Himalaya modulated the downward transport of naturally produced O₃ from the stratosphere to the troposphere.  O₃ concentrations above 8 km altitude were consistently higher than median concentrations when the SWJ was centered over or south of the thermal gradient regardless of the velocity and structure of the SWJ.  Active stratosphere-troposphere exchange over the Tibetan plateau increased O₃ concentraton over the Himalaya to up to 100 parts per billion as low as 9 km altitude.  These results provide important constraints for relative contributions of pollutant versus natural sources to tropospheric O₃ within the region.

(3) Soluble trace gases, the composition of particulate matter, and related meteorological conditions were measured in the Kathmandu valley, Nepal during April 2015.  Results were interpreted in conjunction with thermodynamic model calculations to characterize processes that influence the gas-aerosol phase partitioning of these compounds and to evaluate related implications for regional air quality.  Large day-night variability in temperature and RH drove corresponding variability in aerosol liquid water content, which in turn modulated variability in (1) the gas-aerosol phase partitioning of ammonia (NH₃), nitric acid (HNO₃), and hydrochloric acid (HCl) and (2) aerosol solution acidity.  Aerosol acidities expressed as pH ranged from 2.2 to 3.3.  To provide context, the pH of vinegar is approximately 2.8.  Total oxidized sulfur (gaseous sulfur dioxide + particulate sulfate) was systematically higher during nighttime relative to daytime by factors of 2 to 5, which suggests that chemically distinct air was transported to the sampling site via an alternating up-valley - down-valley flow regime over day-night cycles.  Total ammonia (gaseous NH₃ + particulate ammonium) exhibited day-night patterns similar to those of total oxidized sulfur although relative differences were proportionately smaller (typically less than a factor of 2).  Day-night differences in total nitrate (gaseous HNO₃ + particulate nitrate) and total chlorine (gaseous HCl + particulate chloride) were somewhat more variable but also tended to be higher at night than during the day.  Most total chlorine measured during the campaign originated from the combustion of biomass, fossil fuels, and/or garbage within the region.  Concentrations of gaseous inorganic bromine (Br) and gaseous HCl fell within the ranges of those measured in marine air, which in the presence of acidic aerosol solutions supports the hypothesis that multiphase chemical processes involving both Br and Cl radicals impacted regional air quality in the Kathmandu valley during the campaign.

The graduate student at UVA who was supported through the project gained valuable hands-on experience in this line of research via active engagement in developing the research strategy, participation in the planning meeting and field experiment, integrating and interpreting data, presenting results at a workshop and three scientific conferences, and preparing manuscripts for publication.  Project results contributed directly to her Ph.D. dissertation. The project also fostered international disciplinary and interdisciplinary research and educational collaborations involving faculty, scientific staff, and students at five academic institutions in the US and two research institutions in Nepal.  Project results have improved understanding of processes that modulate regional atmospheric chemistry thereby facilitating the design of mitigation strategies to improve air quality in the Kathmandu valley, over broader regions of south Asia, and elsewhere globally.  These results also contribute to the development of reliable predictive capabilities for the composition and oxidizing capacity of Earth's atmosphere, the direct and indirect influences of greenhouse gases and aerosols on radiative transfer and climate, the cycling and deposition fluxes of atmospheric nutrients to Earth's surface, impacts on heath, and related feedbacks. 

Last Modified: 09/13/2017
Modified by: William C Keene