Variability of ambient black carbon concentration in the Central Himalaya and its assessment over the Hindu Kush Himalayan region.

During 2015-2018, eight black carbon (BC) monitoring sites were established in Nepal and Bhutan to fill a significant data gap regarding BC measurement in Central Himalaya. This manuscript analyzes and presents data from these eight stations and one additional station on the Tibetan plateau (TP). Complex topography, varied emission sources, and atmospheric transport pathways significantly impacted the BC concentrations across these stations, with annual mean concentrations varying from 36 ng m-3 to 45,737 ng m-3. Higher annual mean concentrations (5609 ± 4515 ng m-3) were recorded at low-altitude sites than in other locations, with seasonal concentrations highest in the winter (7316 ± 2541 ng m-3). In contrast, the annual mean concentrations were lowest at high-altitude sites (376 ± 448 ng m-3); the BC concentrations at these sites peaked during the pre-monsoon season (930 ± 685 ng m-3). Potential source contributions to the total observed BC were analyzed using the absorption angstrom exponent (AAE). AAE analysis showed the dominance of biomass burning sources (>50 %), except in Kathmandu. By combining our data with previously published literature, we put our measurements in perspective by presenting a comprehensive assessment of BC concentrations and their variability over the Hindu Kush Himalayan (HKH) region. The BC levels in all three geographic regions, high, mid, and low altitude significantly influenced by the persistent seasonal meteorology. However, the mid-altitude stations were substantially affected by valley dynamics and urbanization. The low-altitude stations experienced high BC concentrations during the winter and post-monsoon seasons. Concentration weighted trajectory (CWT) and frequency analyses revealed the dominance of long-range transported pollution during winter over HKH, from west to east. South Asian sources remained significant during the monsoon season. During pre- and post-monsoon, the local, regional, and long-distance pollution varied depending on the location of the receptor site.

Submicron Aerosol Composition and Source Contribution across the Kathmandu Valley, Nepal, in Winter.

The Kathmandu valley experiences an average wintertime PM1 concentration of ∼100 µg m-3 and daily peaks over 200 µg m-3. We present ambient nonrefractory PM1 chemical composition, and concentration measured by a mini aerosol mass spectrometer (mAMS) sequentially at Dhulikhel (on the valley exterior), then urban Ratnapark, and finally suburban Lalitpur in winter 2018. At all sites, organic aerosol (OA) was the largest contributor to combined PM1 (C-PM1) (49%) and black carbon (BC) was the second largest contributor (21%). The average background C-PM1 at Dhulikhel was 48 µg m-3; the urban enhancement was 120% (58 µg m-3). BC had an average of 6.1 µg m-3 at Dhulikhel, an urban enhancement of 17.4 µg m-3. Sulfate (SO4) was 3.6 µg m-3 at Dhulikhel, then 7.5 µg m-3 at Ratnapark, and 12.0 µg m-3 at Lalitpur in the brick kiln region. Chloride (Chl) increased by 330 and 250% from Dhulikhel to Ratnapark and Lalitpur on average. Positive matrix factorization (PMF) identified seven OA sources, four primary OA sources, hydrocarbon-like (HOA), biomass burning (BBOA), trash burning (TBOA), a sulfate-containing local OA source (sLOA), and three secondary oxygenated organic aerosols (OOA). OOA was the largest fraction of OA, over 50% outside the valley and 36% within. HOA (traffic) was the most prominent primary source, contributing 21% of all OA and 44% of BC. Brick kilns were the second largest contributor to C-PM1, 12% of OA, 33% of BC, and a primary emitter of aerosol sulfate. These results, though successive, indicate the importance of multisite measurements to understand ambient particulate matter concentration heterogeneity across urban regions.

Emission factors and emission inventory of diesel vehicles in Nepal.

A comprehensive emission inventory of the transport sector through fuel-based emission factors (EFs) was developed for the first time in Nepal. This study estimates air pollutants emission from diesel vehicles between the years 1989 and 2018 based on national statistical data, average vehicle kilometers travelled, fuel mileage, and measurement-based EFs for each vehicle category during idle and moving conditions. The consumption of diesel by vehicle category was also estimated and total consumption was compared with national sales data. The Monte Carlo was used to estimate uncertainties. Nationally, total diesel consumption was estimated as 892,770 kL (85-115%) in 2017/18, 13.4 times higher than 1989/90. Ratnoze1 and Microaeth were used to conduct the tail pipe emission measurements. The fuel-based EFs of CO2, CO, BC, and PM2.5 were calculated through the carbon mass balance method. Of all diesel vehicles measured (n = 29) during idling, the average EFs were estimated as CO2 2600 (99-101%), CO 33.3 (44-156%), BC 0.6 (25-101%), and PM2.5 5.2 (0-235%) in unit of g L-1. For moving conditions (n = 5), the average EFs were estimated to be CO2 2476 (90-110%), CO 97.3 (0-232%), BC 1.7 (46-110%), and PM2.5 20.7 (0-255%), all in g L-1. Multiplying fuel consumption by EFs, national air pollutant emissions were estimated as 2214 (90-110%) to 2781(85-115%) for CO2, 27.7 (42-158%) to 88.8 (0-232%) for CO, 0.51 (23-177%) to 3.55 (46-110%) for BC and 3.42 (0-236%) to 23.47 (0-255%) for PM2.5 in 2017/18 in unit of Gg. This paper recommends revising national vehicle mass emission standards based on the findings of this study and including and enhancing sustainable low-carbon transport through amendment of transport policy.

Black carbon concentration in the central Himalayas: Impact on glacier melt and potential source contribution.

This study discusses year-long (October 2016-September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28°12'49.21″N, 85°36'33.77″E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 µg m-3) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96-542 ng g-1 and 152-827 ng g-1, respectively. The source apportionment study using the absorption Ångström exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated ∼14% contribution of BC from open-burning and ∼77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model - Snow, Ice, and Aerosol Radiation - was in the range of 0.8-3.8% during the pre-monsoon season. The glacier mass balance analysis suggested that BC contributed to approximately 39% of the total mass loss in the pre-monsoon season.

Cookstove Smoke Impact on Ambient Air Quality and Probable Consequences for Human Health in Rural Locations of Southern Nepal.

Residential emission from traditional biomass cookstoves is a major source of indoor and outdoor air pollution in developing countries. However, exact quantification of the contribution of biomass cookstove emissions to outdoor air is still lacking. In order to address this gap, we designed a field study to estimate the emission factors of PM2.5 (particulate matter of less than 2.5 µ diameter) and BC (black carbon) indoors, from cookstove smoke using biomass fuel and with smoke escaping outdoors from the roof of the house. The field study was conducted in four randomly selected households in two rural locations of southern Nepal during April 2017. In addition, real-time measurement of ambient PM2.5 was performed for 20 days during the campaign in those two rural sites and one background location to quantify the contribution of cooking-related emissions to the ambient PM2.5. Emission factor estimates indicate that 66% of PM2.5 and 80% of BC emissions from biomass cookstoves directly escape into ambient air. During the cooking period, ambient PM2.5 concentrations in the rural sites were observed to be 37% higher than in the nearby background location. Based on the World Health Organization (WHO)'s AirQ+ model simulation, this 37% rise in ambient PM2.5 during cooking hours can lead to approximately 82 cases of annual premature deaths among the rural population of Chitwan district.

A model-ready emission inventory for crop residue open burning in the context of Nepal.

Open burning of crop residue is an important source of air pollution which is poorly characterized in South Asia. Currently, the gridded inventory reported by Global Fire Emissions Database for biomass burning including open burning of crop residue are of coarse resolution (0.25° × 0.25°), and may not be appropriate for a simulation for Nepal. This study develops a comprehensive high resolution (1 km × 1 km) gridded model-ready emissions inventory for Nepal to understand the spatial characteristics of air pollutant emissions from open burning. We estimate the national air pollutant emissions from crop residue burned between the years 2003 and 2017. The best available data on agricultural production, residue consumption patterns, agricultural burning parameters and emission factors were derived from secondary sources. The Monte Carlo method was used to estimate uncertainties. The mass of crop residue burned in 2016/17 was 2908 Gg (61-139%), which was 22% of the dry matter generated that year. By multiplying the burned crop residue mass by emission factors, the air pollutant emissions were estimated as 4140 for CO2 (56-144%), 154 for CO (4-196%), 6.5 for CH4 (7-193%), 1.2 for SO2 (60-140%), 24.5 for PM2.5 (30-170%), 8.6 for OC (38-162%), 2.2 for BC (-1-201%), 7 for NOx (54-146%), 22.5 for NMVOC (8-192%) and 2.7 for NH3 (3-197%) in unit of Gg yr-1. More than 80% of air pollutants were generated during the months of February to May from the open burning of crop residue. The findings of this paper indicate that substantial reduction in open field burning would dramatically improve air quality in both the Terai region and other parts of Nepal and help reduce negative health impacts associated with the open burning of residue such as premature deaths, respiratory disease, and cardiovascular disease.

Proinflammatory Effects in Ex Vivo Human Lung Tissue of Respirable Smoke Extracts from Indoor Cooking in Nepal.

Rationale: Exposure to biomass smoke is believed to increase the risk of developing chronic obstructive pulmonary disease. However, little is known about the mechanisms underlying responses to biomass smoke in human lungs.Objectives: This study had two objectives: first, to quantify "real-life" exposures to particulate matter <2 µm in diameter (PM2.5) and carbon monoxide (CO) measured during cooking on stoves in rural areas of Nepal in different geographical settings; and second, to assess the effect of biomass smoke extracts on inflammatory responses in ex vivo human lung tissue.Methods: Personal exposures to PM2.5 and indoor near-stove CO concentrations were measured during cooking on a range of stoves in 103 households in 4 different Nepalese villages situated at altitudes between ∼100 and 4,000 m above sea level. Inflammatory profiles to smoke extracts collected in the field were assessed by incubating extracts with human lung tissue fragments and subsequent Luminex analysis.Results: In households using traditional cooking stoves, the overall mean personal exposure to PM2.5 during cooking was 276.1 µg/m3 (standard deviation [SD], 265 µg/m3), and indoor CO concentration was 16.3 ppm (SD, 19.65 ppm). The overall mean PM2.5 exposure was reduced by 51% (P = 0.04) in households using biomass fuel in improved cook stoves, and 80% (P < 0.0001) in households using liquefied petroleum gas. Similarly, the indoor CO concentration was reduced by 72% (P < 0.001) and 86% (P < 0.0001) in households using improved cook stoves and liquefied petroleum gas, respectively. Significant increases occurred in 7 of the 17 analytes measured after biomass smoke extract stimulation of human lung tissue (IL-8 [interleukin-8], IL-6, TNF-α [tumor necrosis factor-α], IL-1ß, CCL2, CCL3, and CCL13).Conclusions: High levels of real-life exposures to PM2.5 and CO occur during cooking events in rural Nepal. These exposures induce lung inflammation ex vivo, which may partially explain the increased risk of chronic obstructive pulmonary disease in these communities.

Ambient endotoxin in PM10 and association with inflammatory activity, air pollutants, and meteorology, in Chitwan, Nepal.

BACKGROUND: Endotoxin associated with ambient PM (particulate matter) has been linked to adverse respiratory symptoms, but there have been few studies of ambient endotoxin and its association with co-pollutants and inflammation. OBJECTIVES: Our aim was to measure endotoxin associated with ambient PM10 (particulate matter with aerodynamic diameter<10µm) in summer 2016 at four locations in Chitwan, Nepal, and investigate its association with meteorology, co-pollutants, and inflammatory activity. METHODS: PM10 concentrations were recorded and filter paper samples were collected using E-samplers; PM1, PM2.5, black carbon (BC), methane (CH4), and carbon monoxide (CO) were also measured. The Limulus amebocyte lysate (LAL) assay was used for endotoxin quantification and the nuclear factor kappa B (NFκB) activation assay to assess inflammatory activity. RESULTS: The mean concentration of PM10 at the different locations ranged from 136 to 189µg/m3, and of endotoxin from 0.29 to 0.53EU/m3. Pollutant presence was positively correlated with endotoxin. Apart from relative humidity, meteorological variations had no significant impact on endotoxin concentration. NF-κB activity was negatively correlated with endotoxin concentration. CONCLUSIONS: To the best of our knowledge, this study provides the first measurements of ambient endotoxin associated with PM10 in Nepal. Endotoxin and co-pollutants were positively associated indicating a similar source. Endotoxin was negatively correlated with inflammatory activity as a result of a time-limited forest fire event during the sampling period. Studies of co-pollutants suggested that the higher levels of endotoxin related to biomass burning were accompanied by increased levels of anti-inflammatory agents, which suppressed the endotoxin inflammatory effect.