A preliminary study of the effects of aircraft noise on families who reside in close proximity to an airport

Background: The use of air transportation has grown in the last century, escalating the noise exposure of families residing in close proximity to airports. The audiological effects need to be assessed to determine the impact of this increase on children and young adults living near to airports in South Africa. Method: Hearing patterns for these individuals were compared to those residing 30 km away from the airport. Sixty people, between the ages of 12-30 years, were assessed. Participants completed a questionnaire and were subjected to a diagnostic audiological test battery and tested using diagnostic distortion product otoacoustic emissions (DPOAEs). Results: Participants residing in close proximity to the airport presented with a notch configuration in the high frequencies, as opposed to those who lived further away. DPOAEs indicated a change in hearing in the high frequencies between the test populations. The positive relationship between the pure tone results and the DPOAEs strengthens the claim that aircraft noise has an effect on the hearing patterns of individuals living near to airports. Participants also experienced annoyance resulting from such noise. Conclusion: The results highlight the need for investigation into the hearing of individuals who reside in close proximity to airports. Comprehensive studies will be informative and beneficial to the field of audiology in South Africa. The highlighted health and safety issues require in-depth study to formulate a stronger argument for monitoring the hearing of families who are exposed to aircraft noise.Keywords: aircraft noise exposure, hearing patterns, distortion product otoacoustic emissions (DPOAEs

An overview of airborne measurement in Nepal – Part 1: Vertical profile of aerosol size, number, spectral absorption, and meteorology

The paper provides an overview of an airborne measurement campaign with a microlight aircraft over the Pokhara Valley region, Nepal, a metropolitan region in the central Himalayan foothills. This is the first aerial measurement in the central Himalayan foothill region, one of the polluted but relatively poorly sampled regions of the world. Conducted in two phases (in May 2016 and December 2016–January 2017), the goal of the overall campaign was to quantify the vertical distribution of aerosols over a polluted mountain valley in the Himalayan foothills, as well as to investigate the extent of regional transport of emissions into the Himalayas. This paper summarizes results from the first phase where test flights were conducted in May 2016 (pre-monsoon), with the objective of demonstrating the potential of airborne measurements in the region using a portable instrument package (size with housing case: 0.45 m × 0.25 m × 0.25 m, 15 kg) onboard an ultralight aircraft (IKARUS-C42). A total of five sampling test flights were conducted (each lasting for 1–1.5 h) in the Pokhara Valley to characterize vertical profiles of aerosol properties such as aerosol number and size distribution (0.3–2 µm), total particle concentration (>14 nm), aerosol absorption (370–950 nm), black carbon (BC), and meteorological variables. Although some interesting observations were made during the test flight, the study is limited to a few days (and only a few hours of flight in total) and thus the analysis presented may not represent the entire pollution–meteorology interaction found in the Pokhara Valley. The vertical profiles of aerosol species showed decreasing concentrations with altitude (815 to 4500 m a.s.l.); a steep concentration gradient below 2000 m a.s.l. in the morning; and mixed profiles (up to ca. 4000 m a.s.l.) in the afternoon. The near-surface (<1000 m a.s.l.) BC concentrations observed in the Pokhara Valley were much lower than pre-monsoon BC concentrations in the Kathmandu Valley, and similar in range to Indo-Gangetic Plain (IGP) sites such as Kanpur in India. The sampling test flight also detected an elevated polluted aerosol layer (around 3000 m a.s.l.) over the Pokhara Valley, which could be associated with the regional transport. The total aerosol and black carbon concentration in the polluted layer was comparable with the near-surface values. The elevated polluted layer was also characterized by a high aerosol extinction coefficient (at 550 nm) and was identified as smoke and a polluted dust layer. The observed shift in the westerlies (at 20–30∘ N) entering Nepal during the test flight period could be an important factor for the presence of elevated polluted layers in the Pokhara Valle

Participatory policy analysis in health policy and systems research: reflections from a study in Nepal.

Background Participatory policy analysis (PPA) as a method in health policy and system research remains underexplored. Using our experiences of conducting PPA workshops in Nepal to explore the impact of the country’s move to federalism on its health system, we reflect on the method’s strengths and challenges. We provide an account of the study context, the design and implementation of the workshops, and our reflections on the approach’s strengths and challenges. Findings on the impact of federalism on the health system are beyond the scope of this manuscript. Main body We conducted PPA workshops with a wide range of health system stakeholders (political, administrative and service-level workforce) at the local and provincial levels in Nepal. The workshops consisted of three activities: river of life, brainstorming and prioritization, and problem-tree analysis. Our experiences show that PPA workshops can be a valuable approach to explore health policy and system issues – especially in a context of widespread systemic change which impacts all stakeholders within the health system. Effective engagement of stakeholders and activities that encourage both individual- and system-level reflections and discussions not only help in generating rich qualitative data, but can also address gaps in participants’ understanding of practical, technical and political aspects of the health system, aid policy dissemination of research findings, and assist in identifying short- and long-term practice and policy issues that need to be addressed for better health system performance and outcomes. Conducting PPA workshops is, however, challenging for a number of reasons, including the influence of gatekeepers and power dynamics between stakeholders/participants. The role and skills of researchers/facilitators in navigating such challenges are vital for success. Although the long-term impact of such workshops needs further research, our study shows the usefulness of PPA workshops for researchers, for participants and for the wider health system. Conclusions PPA workshops can effectively generate and synthesize health policy and system evidence through collaborative engagement of health system stakeholders with varied roles. When designed with careful consideration for context and stakeholders’ needs, it has great potential as a method in health policy and systems research

Observation and analysis of spatiotemporal characteristics of surface ozone and carbon monoxide at multiple sites in the Kathmandu Valley, Nepal

Residents of the Kathmandu Valley experience severe particulate and gaseous air pollution throughout most of the year, even during much of the rainy season. The knowledge base for understanding the air pollution in the Kathmandu Valley was previously very limited but is improving rapidly due to several field measurement studies conducted in the last few years. Thus far, most analyses of observations in the Kathmandu Valley have been limited to short periods of time at single locations. This study extends the past studies by examining the spatial and temporal characteristics of two important gaseous air pollutants (CO and O3) based on simultaneous observations over a longer period at five locations within the valley and on its rim, including a supersite (at Bode in the valley center, 1345&thinsp;m above sea level) and four satellite sites: Paknajol (1380&thinsp;m&thinsp;a.s.l.) in the Kathmandu city center; Bhimdhunga (1522&thinsp;m&thinsp;a.s.l.), a mountain pass on the valley's western rim; Nagarkot (1901&thinsp;m&thinsp;a.s.l.), another mountain pass on the eastern rim; and Naikhandi (1233&thinsp;m&thinsp;a.s.l.), near the valley's only river outlet. CO and O3 mixing ratios were monitored from January to July 2013, along with other gases and aerosol particles by instruments deployed at the Bode supersite during the international air pollution measurement campaign SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley – endorsed by the Atmospheric Brown Clouds program of UNEP). The monitoring of O3 at Bode, Paknajol and Nagarkot as well as the CO monitoring at Bode were extended until March 2014 to investigate their variability over a complete annual cycle. Higher CO mixing ratios were found at Bode than at the outskirt sites (Bhimdhunga, Naikhandi and Nagarkot), and all sites except Nagarkot showed distinct diurnal cycles of CO mixing ratio, with morning peaks and daytime lows. Seasonally, CO was higher during premonsoon (March–May) season and winter (December–February) season than during monsoon season (June–September) and postmonsoon (October–November) season. This is primarily due to the emissions from brick industries, which are only operational during this period (January–April), as well as increased domestic heating during winter, and regional forest fires and agro-residue burning during the premonsoon season. It was lower during the monsoon due to rainfall, which reduces open burning activities within the valley and in the surrounding regions and thus reduces sources of CO. The meteorology of the valley also played a key role in determining the CO mixing ratios. The wind is calm and easterly in the shallow mixing layer, with a mixing layer height (MLH) of about 250&thinsp;m, during the night and early morning. The MLH slowly increases after sunrise and decreases in the afternoon. As a result, the westerly wind becomes active and reduces the mixing ratio during the daytime. Furthermore, there was evidence of an increase in the O3 mixing ratios in the Kathmandu Valley as a result of emissions in the Indo-Gangetic Plain (IGP) region, particularly from biomass burning including agro-residue burning. A top-down estimate of the CO emission flux was made by using the CO mixing ratio and mixing layer height measured at Bode. The estimated annual CO flux at Bode was 4.9&thinsp;µg&thinsp;m−2&thinsp;s−1, which is 2–14 times higher than that in widely used emission inventory databases (EDGAR HTAP, REAS and INTEX-B). This difference in CO flux between Bode and other emission databases likely arises from large uncertainties in both the top-down and bottom-up approaches to estimating the emission flux. The O3 mixing ratio was found to be highest during the premonsoon season at all sites, while the timing of the seasonal minimum varied across the sites. The daily maximum 8&thinsp;h average O3 exceeded the WHO recommended guideline of 50&thinsp;ppb on more days at the hilltop station of Nagarkot (159 out of 357 days) than at the urban valley bottom sites of Paknajol (132 out of 354 days) and Bode (102 out of 353 days), presumably due to the influence of free-tropospheric air at the high-altitude site (as also indicated by Putero et al., 2015, for the Paknajol site in the Kathmandu Valley) as well as to titration of O3 by fresh NOx emissions near the urban sites. More than 78&thinsp;% of the exceedance days were during the premonsoon period at all sites. The high O3 mixing ratio observed during the premonsoon period  is of a concern for human health and ecosystems, including agroecosystems in the Kathmandu Valley and surrounding regions.</p

Polar opposites? NGOs, left parties and the fight for social change in Nepal

In the early 1990s, when NGOs were rising to prominence as an ostensible force for social change in Nepal, the Maoists were also beginning to organise, and denounced NGOs as agents of imperialism. The Maoists came to prominence by fighting a People’s War launched in 1996, with the intention of improving life for the poor peasant and working-class majority. But after a decade-long struggle, the Maoists became incorporated into the parliamentary system. While Nepal’s first democratic revolution in 1990 met formal, popular political demands, which were consolidated in a subsequent revolution in 2006 overthrowing the monarchy and bringing the People’s War to an end, there was little socio-economic progress for the vast majority. The argument advanced in this article is that this lack of progress relied on the interplay of two phenomena: an anti-Maoist alliance consisting of the international community, the domestic ruling elite and NGOs, and a fundamental ambiguity at the heart of the Maoists’ political theory

Speciated online PM1 from South Asian combustion sources-Part 1: Fuel-based emission factors and size distributions

Combustion of biomass, garbage, and fossil fuels in South Asia has led to poor air quality in the region and has uncertain climate forcing impacts. Online measurements of submicron aerosol (PM1) emissions were conducted as part of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) to investigate and report emission factors (EFs) and vacuum aerodynamic diameter (dva) size distributions from prevalent but poorly characterized combustion sources. The online aerosol instrumentation included a qmini aerosol mass spectrometer (mAMS) and a dual-spot eight-channel aethalometer (AE33). The mAMS measured non-refractory PM1 mass, composition, and size. The AE33-measured black carbon (BC) mass and estimated light absorption at 370 nm due to organic aerosol or brown carbon. Complementary gas-phase measurements of carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) were collected using a Picarro Inc. cavity ring-down spectrometer (CRDS) to calculate fuel-based EFs using the carbon mass balance approach. The investigated emission sources include open garbage burning, diesel-powered irrigation pumps, idling motorcycles, traditional cookstoves fueled with dung and wood, agricultural residue fires, and coal-fired brick-making kilns, all of which were tested in the field. Open-garbage-burning emissions, which included mixed refuse and segregated plastics, were found to have some of the largest PM1 EFs (3.77-19.8 g k-1) and the highest variability of the investigated emission sources. Non-refractory organic aerosol (OA) size distributions measured by the mAMS from garbage-burning emissions were observed to have lognormal mode dva values ranging from 145 to 380 nm. Particle-phase hydrogen chloride (HCl) was observed from open garbage burning and was attributed to the burning of chlorinated plastics. Emissions from two diesel-powered irrigation pumps with different operational ages were tested during NAMaSTE. Organic aerosol and BC were the primary components of the emissions and the OA size distributions were centered at ∼ 80 nm dva. The older pump was observed to have significantly larger EFOA than the newer pump (5.18 g k-1 compared to 0.45 g k-1) and similar EFBC. Emissions from two distinct types of coal-fired brick-making kilns were investigated. The less advanced, intermittently fired clamp kiln was observed to have relatively large EFs of inorganic aerosol, including sulfate (0.48 g k-1) and ammonium (0.17 g k-1), compared to the other investigated emission sources. The clamp kiln was also observed to have the largest absorption Ångström exponent (AAE Combining double low line 4) and organic carbon (OC) to BC ratio (OC: BC Combining double low line 52). The continuously fired zigzag kiln was observed to have the largest fraction of sulfate emissions with an EFSO4 of 0.96 g k-1. Non-refractory aerosol size distributions for the brick kilns were centered at ∼ 400 nm dva. The biomass burning samples were all observed to have significant fractions of OA and non-refractory chloride; based on the size distribution results, the chloride was mostly externally mixed from the OA. The dung-fueled traditional cookstoves were observed to emit ammonium, suggesting that the chloride emissions were partially neutralized. In addition to reporting EFs and size distributions, aerosol optical properties and mass ratios of OC to BC were investigated to make comparisons with other NAMaSTE results (i.e., online photoacoustic extinctiometer (PAX) and off-line filter based) and the existing literature. This work provides critical field measurements of aerosol emissions from important yet under-characterized combustion sources common to South Asia and the developing world

Ambient air quality in the Kathmandu Valley, Nepal, during the pre-monsoon: Concentrations and sources of particulate matter and trace gases

The Kathmandu Valley in Nepal is a bowl-shaped urban basin that experiences severe air pollution that poses health risks to its 3.5 million inhabitants. As part of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE), ambient air quality in the Kathmandu Valley was investigated from 11 to 24 April 2015, during the premonsoon season. Ambient concentrations of fine and coarse particulate matter (PM2:5 and PM10, respectively), online PM1, inorganic trace gases (NH3, HNO3, SO2, and HCl), and carbon-containing gases (CO2, CO, CH4, and 93 nonmethane volatile organic compounds; NMVOCs) were quantified at a semi-urban location near the center of the valley. Concentrations and ratios of NMVOC indicated origins primarily from poorly maintained vehicle emissions, biomass burning, and solvent/gasoline evaporation. During those 2 weeks, daily average PM2:5 concentrations ranged from 30 to 207 μ g m-3, which exceeded the World Health Organization 24 h guideline by factors of 1.2 to 8.3. On average, the nonwater mass of PM2:5 was composed of organic matter (48 %), elemental carbon (13 %), sulfate (16 %), nitrate (4 %), ammonium (9 %), chloride (2 %), calcium (1 %), magnesium (0.05 %), and potassium (1 %). Large diurnal variability in temperature and relative humidity drove corresponding variability in aerosol liquid water content, the gas-aerosol phase partitioning of NH3, HNO3, and HCl, and aerosol solution pH. The observed levels of gas-phase halogens suggest that multiphase halogen-radical chemistry involving both Cl and Br impacted regional air quality. To gain insight into the origins of organic carbon (OC), molecular markers for primary and secondary sources were quantified. Levoglucosan (averaging 1230±1154 ng m-3), 1,3,5-triphenylbenzene (0:8± 0:6 ng m-3), cholesterol (2:9±6:6 ng m-3), stigmastanol (1.0 ±0:8 ng m-3), and cis-pinonic acid (4:5 ± 1:9 ng m-3) indicate contributions from biomass burning, garbage burning, food cooking, cow dung burning, and monoterpene secondary organic aerosol, respectively. Drawing on source profiles developed in NAMaSTE, chemical mass balance (CMB) source apportionment modeling was used to estimate contributions to OC from major primary sources including garbage burning (18 ± 5 %), biomass burning (17 ± 10 %) inclusive of open burning and biomass-fueled cooking stoves, and internal-combustion (gasoline and diesel) engines (18±9 %). Model sensitivity tests with newly developed source profiles indicated contributions from biomass burning within a factor of 2 of previous estimates but greater contributions from garbage burning (up to three times), indicating large potential impacts of garbage burning on regional air quality and the need for further evaluation of this source. Contributions of secondary organic carbon (SOC) to PM2:5 OC included those originating from anthropogenic precursors such as naphthalene (10 ± 4 %) and methylnaphthalene (0:3 ± 0:1 %) and biogenic precursors for monoterpenes (0:13 ± 0:07 %) and sesquiterpenes (5 ± 2 %). An average of 25 % of the PM2.5 OC was unapportioned, indicating the presence of additional sources (e.g., evaporative and/or industrial emissions such as brick kilns, food cooking, and other types of SOC) and/or underestimation of the contributions from the identified source types. The source apportionment results indicate that anthropogenic combustion sources (including biomass burning, garbage burning, and fossil fuel combustion) were the greatest contributors to PM2:5 and, as such, should be considered primary targets for controlling ambient PM pollution

Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE): Emissions of particulate matter from wood-and dung-fueled cooking fires, garbage and crop residue burning, brick kilns, and other sources

The Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) characterized widespread and under-sampled combustion sources common to South Asia, including brick kilns, garbage burning, diesel and gasoline generators, diesel groundwater pumps, idling motorcycles, traditional and modern cooking stoves and fires, crop residue burning, and heating fire. Fuel-based emission factors (EFs; with units of pollutant mass emitted per kilogram of fuel combusted) were determined for fine particulate matter (PM2.5), organic carbon (OC), elemental carbon (EC), inorganic ions, trace metals, and organic species. For the forced-draft zigzag brick kiln, EFPM2.5 ranged from 12 to 19gkg-1 with major contributions from OC (7%), sulfate expected to be in the form of sulfuric acid (31.9%), and other chemicals not measured (e.g., particle-bound water). For the clamp kiln, EFPM2.5 ranged from 8 to 13gkg-1, with major contributions from OC (63.2%), sulfate (23.4%), and ammonium (16%). Our brick kiln EFPM2.5 values may exceed those previously reported, partly because we sampled emissions at ambient temperature after emission from the stack or kiln allowing some particle-phase OC and sulfate to form from gaseous precursors. The combustion of mixed household garbage under dry conditions had an EFPM2.5 of 7.4±1.2gkg-1, whereas damp conditions generated the highest EFPM2.5 of all combustion sources in this study, reaching up to 125±23gkg-1. Garbage burning emissions contained triphenylbenzene and relatively high concentrations of heavy metals (Cu, Pb, Sb), making these useful markers of this source. A variety of cooking stoves and fires fueled with dung, hardwood, twigs, and/or other biofuels were studied. The use of dung for cooking and heating produced higher EFPM2.5 than other biofuel sources and consistently emitted more PM2.5 and OC than burning hardwood and/or twigs; this trend was consistent across traditional mud stoves, chimney stoves, and three-stone cooking fires. The comparisons of different cooking stoves and cooking fires revealed the highest PM emissions from three-stone cooking fires (7.6-73gkg-1), followed by traditional mud stoves (5.3-19.7gkg-1), mud stoves with a chimney for exhaust (3.0-6.8gkg-1), rocket stoves (1.5-7.2gkg-1), induced-draft stoves (1.2-5.7gkg-1), and the bhuse chulo stove (3.2gkg-1), while biogas had no detectable PM emissions. Idling motorcycle emissions were evaluated before and after routine servicing at a local shop, which decreased EFPM2.5 from 8.8±1.3 to 0.71±0.45gkg-1 when averaged across five motorcycles. Organic species analysis indicated that this reduction in PM2.5 was largely due to a decrease in emission of motor oil, probably from the crankcase. The EF and chemical emissions profiles developed in this study may be used for source apportionment and to update regional emission inventories

Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE): Emissions of trace gases and light-absorbing carbon from wood and dung cooking fires, garbage and crop residue burning, brick kilns, and other sources

The Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) campaign took place in and around the Kathmandu Valley and in the Indo-Gangetic Plain (IGP) of southern Nepal during April 2015. The source characterization phase targeted numerous important but undersampled (and often inefficient) combustion sources that are widespread in the developing world such as cooking with a variety of stoves and solid fuels, brick kilns, open burning of municipal solid waste (a.k.a. trash or garbage burning), crop residue burning, generators, irrigation pumps, and motorcycles. NAMaSTE produced the first, or rare, measurements of aerosol optical properties, aerosol mass, and detailed trace gas chemistry for the emissions from many of the sources. This paper reports the trace gas and aerosol measurements obtained by Fourier transform infrared (FTIR) spectroscopy, whole-air sampling (WAS), and photoacoustic extinctiometers (PAX; 405 and 870nm) based on field work with a moveable lab sampling authentic sources. The primary aerosol optical properties reported include emission factors (EFs) for scattering and absorption coefficients (EF Bscat, EF Babs, inm2kg-1 fuel burned), single scattering albedos (SSAs), and absorption Ångström exponents (AAEs). From these data we estimate black and brown carbon (BC, BrC) emission factors (gkg-1 fuel burned). The trace gas measurements provide EFs (gkg-1) for CO2, CO, CH4, selected non-methane hydrocarbons up to C10, a large suite of oxygenated organic compounds, NH3, HCN, NOx, SO2, HCl, HF, etc. (up to ∼ 80 gases in all). The emissions varied significantly by source, and light absorption by both BrC and BC was important for many sources. The AAE for dung-fuel cooking fires (4.63±0.68) was significantly higher than for wood-fuel cooking fires (3.01±0.10). Dung-fuel cooking fires also emitted high levels of NH3 (3.00±1.33gkg-1), organic acids (7.66±6.90gkg-1), and HCN (2.01±1.25gkg-1), where the latter could contribute to satellite observations of high levels of HCN in the lower stratosphere above the Asian monsoon. HCN was also emitted in significant quantities by several non-biomass burning sources. BTEX compounds (benzene, toluene, ethylbenzene, xylenes) were major emissions from both dung- (∼4.5gkg-1) and wood-fuel (∼1.5gkg-1) cooking fires, and a simple method to estimate indoor exposure to the many measured important air toxics is described. Biogas emerged as the cleanest cooking technology of approximately a dozen stove-fuel combinations measured. Crop residue burning produced relatively high emissions of oxygenated organic compounds (∼12gkg-1) and SO2 (2.54±1.09gkg-1). Two brick kilns co-firing different amounts of biomass with coal as the primary fuel produced contrasting results. A zigzag kiln burning mostly coal at high efficiency produced larger amounts of BC, HF, HCl, and NOx, with the halogenated emissions likely coming from the clay. The clamp kiln (with relatively more biomass fuel) produced much greater quantities of most individual organic gases, about twice as much BrC, and significantly more known and likely organic aerosol precursors. Both kilns were significant SO2 sources with their emission factors averaging 12.8±0.2gkg-1. Mixed-garbage burning produced significantly more BC (3.3±3.88gkg-1) and BTEX (∼4.5gkg-1) emissions than in previous measurements. For all fossil fuel sources, diesel burned more efficiently than gasoline but produced larger NOx and aerosol emission factors. Among the least efficient sources sampled were gasoline-fueled motorcycles during start-up and idling for which the CO EF was on the order of ∼700gkg-1 - or about 10 times that of a typical biomass fire. Minor motorcycle servicing led to minimal if any reduction in gaseous pollutants but reduced particulate emissions, as detailed in a companion paper (Jayarathne et al., 2016). A small gasoline-powered generator and an insect repellent fire were also among the sources with the highest emission factors for pollutants. These measurements begin to address the critical data gap for these important, undersampled sources, but due to their diversity and abundance, more work is needed

Variations in surface ozone and carbon monoxide in the Kathmandu Valley and surrounding broader regions during SusKat-ABC field campaign: role of local and regional sources

Air pollution resulting from rapid urbanization and associated human activities in the Kathmandu Valley of Nepal has been leading to serious public health concerns over the past 2 decades. These concerns led to a multinational field campaign SusKat-ABC (Sustainable atmosphere for the Kathmandu Valley – Atmospheric Brown Clouds) that measured different trace gases, aerosols and meteorological parameters in the Kathmandu Valley and surrounding regions during December 2012 to June 2013 to understand local- to regional-scale processes influencing air quality of the Kathmandu Valley. This study provides information about the regional distribution of ozone and some precursor gases using simultaneous in situ measurements from a SusKat-ABC supersite at Bode, Nepal, and two Indian sites: a high-altitude site, Nainital, located in the central Himalayan region and a low-altitude site, Pantnagar, located in the Indo-Gangetic Plain (IGP). The diurnal variations at Bode showed a daytime buildup in O3 while CO shows morning and evening peaks. Similar variations (with lower levels) were also observed at Pantnagar but not at Nainital. Several events of hourly ozone levels exceeding 80&thinsp;ppbv were also observed at Bode. The CO levels showed a decrease from their peak level of about 2000&thinsp;ppbv in January to about 680&thinsp;ppbv in June at Bode. The hourly mean ozone and CO levels showed a strong negative correlation during winter (r2 = 0.82 in January and r2 = 0.71 in February), but this negative correlation gradually becomes weaker, with the lowest value in May (r2 = 0.12). The background O3 and CO mixing ratios at Bode were estimated to be about 14 and 325&thinsp;ppbv, respectively. The rate of change of ozone at Bode showed a more rapid increase ( ∼ 17&thinsp;ppbv&thinsp;h−1) during morning than the decrease in the evening (5–6&thinsp;ppbv&thinsp;h−1), suggesting the prevalence of a semi-urban environ. The lower CO levels during spring suggest that regional transport also contributes appreciably to springtime ozone enhancement in the Kathmandu Valley on top of the local in situ ozone production. We show that regional pollution resulting from agricultural crop residue burning in northwestern IGP led to simultaneous increases in O3 and CO levels at Bode and Nainital during the first week of May 2013. A biomass-burning-induced increase in ozone and related gases was also confirmed by a global model and balloon-borne observations over Nainital. A comparison of surface ozone variations and composition of light non-methane hydrocarbons among different sites indicated the differences in emission sources of the Kathmandu Valley and the IGP. These results highlight that it is important to consider regional sources in air quality management of the Kathmandu Valley.</p