Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources, Meteorological Controls, Regional Trasport, and Implications

International Journal of Multidisciplinary and Innovative Research
ISSN (print): 3050-6883, ISSN (online): 3050-6891
V olume 03 Issue 10 October 2026
DOI: 10.58806/ijmir.2026.v3i10n04
Page No: 847-858
847 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and
Seasonal Variability, Sources, Meteorological Controls, Regional Trasport,
and Implications

Santosh Pandey¹, Kailash Basnet2* Aabiskar Subedi3, Tika Ram Subedi4
1,2,3,4 Prithvi Narayan Campus, Tribhuvan University, Pokhara, Nepal

ABSTRACT ARTICLE DETAILS
Nepal experiences a distinctive aerosol pollution problem produced by the interaction of intense local
emissions, complex mountain -valley meteorology, seasonal biomass and forest burning, and regional
transport from the Indo -Gangetic Plain. This comprehens ive narrative review synthesizes readily
accessible and available scientific literature with the primary objective of improving understanding of
aerosol optical depth (AOD) over Nepal, including its spatial and seasonal variability and the processes
that control it. Evidence from ground -based AERONET observations, satellite remote sensing, surface
particulate-matter monitoring, aerosol chemical characterization, trajectory analysis, atmospheric
modeling, exposure assessment, and health studies is integrated to interpret the broader aerosol
environment. Across Kathmandu, Pokhara, Lumbini, Rara, and high-elevation Himalayan sites, aerosol
loading is generally greatest during winter and pre -monsoon conditions and is reduced during the
summer monsoon by wet scav enging and enhanced atmospheric ventilation. Local emissions,
topography, meteorology, biomass and forest fires, and regional transport from the Indo-Gangetic Plain
jointly shape observed AOD patterns. Surface PM, chemical, and health evidence is used as
complementary information to explain the sources and consequences of columnar aerosol loading. The
review identifies important gaps in long -term observations, geographical coverage, vertical profiling,
chemical characterization, and integration of ground -based and satellite AOD measurements, and
proposes priorities for improving aerosol monitoring and interpretation across Nepal.
KEYWORDS: aerosol optical depth, PM2.5, Kathmandu Valley, Pokhara, Lumbini, Himalayas, source
apportionment, transboundary pollution, meteorology, health burden
Published On:
22 October 2026

Available on:
https://ijmir.com

INTRODUCTION
Atmospheric aerosols are suspended solid and liquid particles that influence visibility, air quality, cloud processes, radiation, climate,
ecosystems, and human health. In Nepal, these effects are amplified by an unusual combination of rapidly growing urba n centers,
widespread combustion sources, dusty roads and construction, seasonal fires, strong monsoon seasonality, and steep terrain.
Kathmandu Valley is a bowlshaped basin in which weak ventilation and nocturnal inversions can retain pollutants near the surface,
while Pokhara and Lumbini are influenced by different combinations of rainfall, elevation, local emissions, and proximity to the
Indo-Gangetic Plain (IGP). High -elevation Himalayan sites may be cleaner on average, yet they remain vulnerable to tra nsported
pollution and episodic fire plumes (Islam et al., 2020; Regmi et al., 2020; Ramachandran & Rupakheti, 2021, 2026).
The literature supplied for this review has an important strength: it approaches the Nepal aerosol problem from multiple
observational scales. AERONET studies characterize column aerosol optical depth (AOD), Ångström exponent, single -scattering
albedo, size distribution, and related optical properties; surface networks quantify PM2.5 and PM10; aerosol mass spectrometry and
filter chemistry identify composition and sources; satellite and land -use analyses describe spatial patterns; Hybrid Single -Particle
Lagrangian Integrated Trajectory (HYSPLIT), Potential Source Contribution Function (PSCF), and Concentration -Weighted
Trajectory (CWT) studies examine transport and atmospheric processes; and exposure and burden -of-disease studies translate
pollution into human consequences (Zhong et al., 2019; Werden et al., 2022; Islam et al., 2022; Kafle et al., 2025; Adhikari et al.,
2026).

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
848 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
A comprehensive review of aerosol pollution over Nepal is needed because the available evidence remains geographically uneven
and fragmented across different observational approaches, locations, and time periods. Nepal's complex topography, ranging from
the lowland Terai to enclosed urban valleys and the high Himalaya, together with strong monsoon seasonality, local emissions,
biomass and forest fires, and regional transport from the Indo -Gangetic Plain, produces substantial spatial and temporal variability
in aerosol loading. Consequently, findings from a single location, particularly the extensively studied Kathmandu Valley, can not
adequately represent aerosol conditions across the country. Moreover, existing studies use different approaches, including gr ound-
based AERONET observations, satellite remote sensing, surface particulate -matter measurements, chemical characterization,
trajectory analysis, and atmospheric modeling, making an integrated synthesis necessary to understand the overall aerosol
environment. This review therefore brings together the readily accessible and available evidence to develop a comprehensive
understanding of AOD over Nepal , while using surface PM, aerosol chemistry, meteorology, and transport studies to explain the
processes controlling its variability. Specifically, the review addresses four questions: (1) What are the dominant aerosol sources
and characteristics across Nepal? (2) How do seasonality, meteorology, topography, and long -range transport influence AOD and
aerosol beha vior? (3) How consistent are the findings across measurement approaches and geographic locations? and (4) What
major observational and knowledge gaps must be addressed to improve aerosol monitoring, interpretation, and air -quality
management in Nepal?

REVIEW APPROACH AND SCOPE

Figure 1. Integrated causal framework for aerosol pollution in Nepal. The review is organized around the pathway from
emissions and regional inflow through atmospheric processing and observed aerosol to exposure and health/climate
consequences.

This article presents a comprehensive narrative review of aerosol optical depth (AOD) and aerosol pollution over Nepal, with the
primary objective of improving understanding of the spatial and temporal characteristics of AOD across the country. Relevant studies
were collected from the scientific literature based primarily on their relevance to aerosol characteristics over Nepal and th eir
accessibility and availability to the authors. The evidence includes ground-based AERONET observations, satellite remote sensing,
surface particulate-matter measurements, aerosol chemical characterization, meteorological observations, trajectory analysis, and
atmospheric modeling. Studies addressing particulate matter, aerosol composition, regional transport, exposure, and health impacts
were also considered when they provided complementary evidence useful for interpreting AOD patterns and the broader aerosol
environment of Nepal. The literature was organized thematically to synthesize AOD magnitude and seasonality, aerosol o ptical
properties, geographical differences, meteorological influences, emission sources, and regional transport. This article is th erefore a
comprehensive narrative review rather than a systematic review or meta -analysis. The literature was not identified through a
predefined systematic-review protocol, exhaustive multi -database search, or formal PRISMA -based screening procedure; instead,
the aim was to bring together readily accessible and available scientific evidence relevant to aerosol loading over Nep al and
synthesize it into a coherent understanding of AOD, its controlling processes, associated pollution characteristics, and rema ining
research gaps.
The studies were grouped into eight evidence domains: (a) aerosol optical properties and climatology; (b) PM2.5, PM10, and urban–
remote contrasts; (c) chemical composition and source apportionment; (d) meteorological, land -use, wildfire, and long -range
transport controls; (e) vertical structure and radiative effects; (f) regional and long -range transport; (g) personal and
microenvironmental exposure; and (h) mortality, health burden, and economic consequences. Greater interpretive weight was given

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
849 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
to multiyear measurements, chemically resolved observations, multi -site studies, and analyses that combined independent data
streams.

Figure 2. | Geographic distribution of the reviewed aerosol studies in Nepal. Studies are grouped according to their
primary geographic focus; multi-site, national, and regional studies are shown separately to avoid duplicate counting.

The geographic distribution of the reviewed literature is uneven, with the largest concentration of sitespecific studies focu sed on
Kathmandu Valley. Pokhara Valley and high-Himalayan locations form smaller evidence clusters, whereas Lumbini, eastern Nepal,
western Nepal/Rara, and southern Nepal are represented by comparatively fewer location -specific studies. Multi-site, national, and
regional investigations provide broader spatial context but do not replace sustained observations at underrepresented locations. This
imbalance should be considered when interpreting national aerosol patterns and highlights the need for expanded long -term AOD
and complementary aerosol monitoring beyond Kathmandu.
Geographic Context: Why Nepal Produces Strong Aerosol Gradients
Nepal spans the southern Himalayan foothills, deeply incised valleys, densely populated urban basins, and high -elevation
environments within a short north –south distance. This geography creates sharp gradients in emissions, boundary -layer depth,
rainfall, and transport. Kathmandu Valley concentrates population, vehicles, construction, industry, brick kilns, waste burning, and
household combustion within terrain that restricts dispersion. The result is a persistent urban enhancement superimposed on a
regional South Asian aerosol background (Islam et al., 2020, 2022; Werden et al., 2023).
Pokhara has a different atmospheric setting. It is a rapidly urbanizing valley but receives very high monsoon rainfall and is directly
adjacent to steep Himalayan terrain. Long -term AERONET analyses show that its aerosol column is nevertheless substantiall y
affected by biomass burning, urban -industrial emissions, dust, and transported pollution, especially in the pre -monsoon season
(Regmi et al., 2020; Ramachandran & Rupakheti, 2021). Lumbini, by contrast, lies at low elevation close to the IGP and is exposed
to local industrial and traffic sources as well as regional inflow; optical studies consistently characterize it as a compara tively
polluted Nepalese site (Jha et al., 2021; Sapkota et al., 2023a; Rijal et al., 2025).
The contrast with remote environments is equally important. Comparative observations show much lower particle concentrations at
Rara Lake than in central Kathmandu, while high -elevation Himalayan sites generally have lower AOD than the IGP and foothill
locations. Yet remote does not mean isolated: Western Nepal measurements at Rara demonstrate that regional forest fires and
southerly transport can produce substantial episodic PM2.5 enhancements (Chalise et al., 2025; Maharjan et al., 2026;
Ramachandran & Rupakheti, 2026).

AEROSOL OPTICAL PROPERTIES AND CLIMATOLOGY
Historical and high-elevation perspective
Longer historical records broaden the geographic and process context beyond the recent AERONETcentered literature. Early
observations in the Nepal Himalaya showed that both carbonaceous aerosol and mineral dust contribute strongly to seasonal aerosol

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
850 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
properties, establishing that Himalayan aerosol is a mixed system rather than a purely urban combustion plume (Carrico et al., 2003).
At the Nepal Climate Observatory–Pyramid, continuous observations documented synoptic-scale dust transport to >5 km elevation,
while later regional work demonstrated pre -monsoon accumulation of aerosol along the Indo -Gangetic Plain and southern
Himalayan slopes (Duchi et al., 2011; Gautam et al., 2011). These studies are important because they show that elevated and remote
sites can receive episodic aerosol from distant source regions even when local emissions are weak.
Additional Nepal studies reinforce the spatial heterogeneity of column aerosol. Acharya et al. (2020) compared AERONET sites in
Nepal using spectral AOD analysis, while measurements at Jomsom and other high-mountain locations demonstrate that elevation,
valley geometry, and season produce optical regimes distinct from lowland and urban basins (Shrestha et al., 2015). The supplie d
evidence therefore supports treating Nepal as a connected vertical transect —from the Terai and IGP -influenced lowlands through
urban valleys to the high Himalaya—rather than as a single air-quality domain.
Pokhara Valley
The most internally consistent optical evidence comes from Pokhara. Regmi et al. (2020) analyzed AERONET observations from
2010–2018 and reported the highest seasonal AOD during pre -monsoon conditions, followed by winter, post -monsoon, and
monsoon. Their trajectory, fire, and size-distribution analyses pointed to a mixture of biomass -burning, urban-industrial, and dust
aerosols, including longrange transport. Ramachandran and Rupakheti (2021), using 2010–2017 observations, independently found
a recurring an nual AOD maximum in the pre -monsoon and minimum during the monsoon, with fire counts closely aligned with
enhanced aerosol loading. The exceptionally strong 2016 pre -monsoon aerosol episode coincided with unusually high fire activity,
strengthening the source interpretation.
The consistency across nonoverlapping time windows is important: the seasonal pattern is not an artifact of a single year or
instrument campaign. It reflects a robust interaction among seasonal burning, regional transport, urban emissions, aerosol gr owth,
and monsoon removal.

LUMBINI AND MULTI-SITE COMPARISONS
Evidence from eastern Nepal
The archive also adds evidence from eastern Nepal, an area underrepresented in many national syntheses. Dahal et al. (2022a)
reported festival-associated perturbations in AOD and column CO over Birtamode, illustrating how short -lived changes in local
activity can be detected jointly by ground and satellite observations. A second study from the eastern Himalayan foothills
characterized post -monsoon and winter aerosol optical behavior and source influences, further showing that the eastern border
region is affected by a mixture of local emissions and regional transport (Dahal et al., 2022b). These studies strengthen the case for
a national network that includes eastern Nepal rather than concentrating monitoring only in Kathmandu and central Nepal.
Lumbini studies reveal both similarities and contrasts. Jha et al. (2021) compared seven Nepalese tourist and high-altitude locations
and found spring or winter enhancement at many sites, with vegetation fires, land clearing, biomass burning, brick kilns, factories,
and vehicles offered as major explanations. Sapkota et al. (2023a) examined Lumbini from 2013 –2019 and reported high AOD
outside the monsoon, low visibility, and seasonal changes consistent with mixtures of biomass -burning and anthropogenic aerosol.
Rijal et al. (2025) further examined AOD, Ångström parameters, rainfall, and relative humidity in Lumbini, emphasizing that
meteorological variables alter aerosol loading and optical behavior but do not act independently of emissions.
A direct comparison of Lumbini, Pokhara, and Langtang Base Camp found substantially lower aerosol loading and much greater
visibility at the high-elevation Langtang site, while Lumbini exhibited stronger pollution sites (Sapkota et al., 2023b). This elevation
gradient is reinforced by the regional synthesis of Ramachandran and Rupakheti (2026), who found AOD across much of the IGP
and Himalayan foothills to be markedly higher than at high-altitude Himalayan locations. Together, these studies show that altitude
and distance from dense emission regions are major determinants of background aerosol burden, although transported pollution can
episodically erode the high-altitude advantage.
AOD, Water Vapor, and Interpretation Limits
Satellite and data-fusion advances
Recent data-fusion work extends the surface –column comparison problem into areas with sparse monitoring. Lamichhane et al.
(2026) integrated satellite AOD, trace gases, and meteorological reanalysis to estimate PM2.5 and long -term trends in southern
Nepal, reporting substantially better predictive performance for a multivariable model than for a simple linear approach. This
direction is promising for the Terai and Dun valleys, but it does not remove the need for ground calibration: satellite AOD i s a
column quantity, and its translation to surface PM2.5 remains sensitive to humidity, aerosol type, boundary-layer height, and vertical
structure.
Sapkota et al. (2023c) compared AERONET AOD and precipitable water at Kathmandu-Bode and four international sites. The study
demonstrates that aerosol –water relationships vary by climatic regime and season. This is an important caution for interpreting
correlations: a positive AOD –water-vapor association can arise from hygroscopic particle growth, common seasonal forcing, or

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
851 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
coincident transport, whereas rainfall can rapidly remove particles. Consequently, AOD should not be treated as a direct surr ogate
for surface PM2.5 without accounting for vertical aerosol distribution, humidity, boundary-layer structure, and aerosol type. Regmi
et al. (2023) addressed this issue directly by comparing low -cost surface PM2.5 with satellite column AOD over Kathmandu,
showing both the value and the limitations of cross-platform relationships.
Surface Particulate Matter: Magnitude, Seasonality, and Spatial Contrast
Surface measurements show that the aerosol problem is not only a column -integrated optical phenomenon. In Kathmandu, winter
and pre-monsoon PM2.5 frequently reach levels associated with serious health concern. Islam et al. (2022) measured daily winter
PM2.5 at urban Ratnapark, suburban Lalitpur, and rural Dhulikhel and found high concentrations at all three sites, with the urban
and suburban locations substantially more polluted than the rural rim site. Their PM10 measurements were even higher,
demonstrating an important coarse -particle contribution from road and crustal material in addition to combustion -derived fine
particles.
Regmi et al. (2023) reported a strong seasonal cycle in Kathmandu low-cost sensor PM2.5, with winter highest and summer lowest,
as well as a bimodal diurnal pattern associated with morning and evening activity and shallow mixing. A 2021 –2023 observational
analysis similarly identified meteorology as a major driver of day-to-day Kathmandu air quality, reinforcing the role of temperature,
humidity, rainfall, and wind in controlling accumulation and removal (Telee et al., 2026). These studies are consistent wi th the
chemical campaigns: emissions remain substantial throughout the year, but meteorological ventilation and wet scavenging strongly
determine the concentrations people actually breathe.
Pokhara surface monitoring provides an important second-city perspective. Pandey et al. (2024) compared three monitoring stations
and found the clearest PM2.5 deterioration in winter, while PM10 patterns were less uniformly severe. This spatial heterogene ity
within one valley cautions against representing an entire city with a single monitor. In a national urban–remote comparison, Chalise
et al. (2025) found much higher PM2.5 and PM10 at Ratnapark in Kathmandu than at Rara Lake, with minima during the rainy
season at both sites. The PM2.5/PM10 ratio also suggested a stronger fine -particle dominance at the urban site, consistent with
combustion sources.

CHEMICAL COMPOSITION AND SOURCE APPORTIONMENT IN KATHMANDU V ALLEY
Vertical structure and radiative effects
Airborne and radiative studies add a dimension that surface monitoring cannot provide. Microlightaircraft measurements over t he
Pokhara region showed strong vertical gradients in aerosol number, size and absorption, with the largest concentrations concentrated
in the lower atmosphere and substantial changes with altitude (Singh et al., 2019). In Kathmandu, SusKat-ABC observations linked
winter aerosol optical properties to radiative effects under severe pollution conditions (Cho et al., 2017), while Thapa e t al. (2017)
quantified aerosol -related modification of solar radiation in the mid -hills. At a remote site near Yala Glacier, Rai et al. (2019)
estimated aerosol radiative forcing, demonstrating that aerosol climate effects extend into cryospheric environm ents.
The regional climate implication is now clearer. Ramachandran et al. (2023) showed that aerosol absorption and radiative effe cts
can warm the Himalayan atmosphere, while Ramachandran and Rupakheti (2026b) synthesized aerosol composition and radiative
forcing across the IGP –Himalaya system. These findings expand the policy relevance of Nepal aerosol research beyond visibility
and cardiopulmonary health: absorbing aerosol can alter atmospheric heating, stability, snow/ice energy balance, and potentia lly
regional circulation. Climate and air -quality objectives are therefore partly coupled, particularly for black carbon and other light -
absorbing particles.
Pre-Monsoon Composition
The NAMaSTE campaign provides the most detailed chemical picture of Kathmandu aerosol. Islam et al. (2020) measured PM,
inorganic gases, carbon -containing gases, and a large suite of non -methane volatile organic compounds during the 2015 pre -
monsoon. Sourc e markers indicated contributions from poorly maintained vehicles, biomass burning, garbage burning, cooking,
dung burning, and secondary organic aerosol formation. The study also showed that temperature and relative humidity influence d
aerosol liquid water, gas–particle partitioning, and aerosol acidity, demonstrating that meteorology changes not only concentration
but also chemical state.
High-resolution aerosol mass spectrometry further resolved the submicron mixture. Werden et al. (2022) found organic aerosol to
be the largest nonrefractory component during the pre -monsoon and identified traffic, biomass burning, trash burning, local/bric k-
kiln-related emissions, and secondary oxygenated organic aerosol. Werden's (2021) dissertation integrates these source -
apportionment datasets and emphasizes the coexistence of strong primary combustion sources with substantial atmospheric
processing. The key policy implication is that controlling only one source category cannot eliminate Kathmandu's PM burden.

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
852 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
Winter Composition and Spatial Heterogeneity
Winter observations show an even stronger accumulation regime. Werden et al. (2023) conducted sequential measurements at
Dhulikhel, Ratnapark, and Lalitpur and found organic aerosol and black carbon to be major components, with a clear urban
enhancement. P ositive matrix factorization identified hydrocarbon -like organic aerosol associated with traffic, biomass -burning
aerosol, trash-burning aerosol, a sulfate-containing local source, and multiple oxygenated secondary factors. Traffic was a prominent
primary source, while brick kilns contributed importantly to black carbon, sulfate, and organic aerosol. The spatial differences
among the three sites demonstrate that source influence varies substantially over short distances.
Islam et al. (2022) reached a complementary conclusion using fine and coarse particulate chemistry. Organic and elemental car bon
dominated much of PM2.5, while resuspended crustal material contributed strongly to PM10. Chemical mass balance modeling
identified garbage burning, biomass burning, and fossil -fuel combustion as major organic-carbon sources, together with secondary
organic aerosol. This result is especially important because it connects visible urban dust with less visible but health -relevant
combustion and secondary fine particles: both coarse and fine fractions require management, but their sources and controls diffe r.
Vehicles and Brick Kilns
Zhong et al. (2019) quantified emissions from vehicles and brick kilns and evaluated their effects with WRF -Chem. Updating the
vehicle inventory reduced model bias for elemental carbon, while updating brick-kiln emissions improved sulfur dioxide simulation.
The study demonstrates a recurring problem in South Asian air -quality modeling: generic regional inventories can substantially
misrepresent local technologies and operating conditions. Nepal -specific emission factors and activity data are therefore essen tial
for credible policy modeling.
Traffic exposure is also visible at the microenvironment scale. Dhital et al. (2014) measured air pollution inside Kathmandu public
transport vehicles and found severe particulate pollution, especially PM10, along with BTEX compounds and evidence that
congestion increased gaseous pollutant exposure. This older study remains relevant because it shows that ambient monitoring alone
may underestimate exposure for commuters who spend time directly within traffic plumes.

Meteorological Controls, Topography, and Seasonal Removal

Figure 3. | Seasonal–geographic synthesis. The matrix summarizes recurring relative patterns across the supplied studies
and should not be interpreted as a quantitative inter-site comparison.

Across the evidence base, meteorology acts as a multiplier of emissions. During winter, shallow boundary layers, stable night time
conditions, weak winds, and basin confinement favor accumulation. During pre-monsoon months, stronger mixing can coexist with
major seasonal sources, especially forest and vegetation fires, dust, and regional inflow. During the monsoon, rainfall scave nges
particles, suppresses some open -burning activities, and increases ventilation, producing the most consistent seasonal minimum in
both AOD and surface PM across many Nepalese sites (Regmi et al., 2020; Ramachandran & Rupakheti, 2021; Chalise et al., 2025;
Ramachandran & Rupakheti, 2026).
Kathmandu's topography intensifies these seasonal controls. Pollutants emitted within the basin can accumulate overnight and during
stagnant episodes, while daytime upslope and valley circulations partially ventilate the basin. Telee et al. (2026) show tha t
meteorological variability remains strongly associated with observed air -quality changes even in recent years. The implication is

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
853 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
practical: emission control and forecasting should be meteorology aware. The same emission rate can produce very different
exposure depending on boundary-layer depth, wind direction, precipitation, and inversion strength.
Land cover adds another spatial dimension. Shrestha et al. (2025) assessed 2023 summer AOD in relation to land -use/land-cover
indicators across Kathmandu Valley and reported lower aerosol loading over more vegetated areas and higher loading associated
with built-up and other non-vegetated surfaces. Although satellite AOD and land-cover correlations cannot by themselves establish
causation, the result supports the broader evidence that urban form, vegetation, emission density, and surface characteristics jointly
shape the spatial aerosol field.
Regional Transport, the Indo-Gangetic Plain, and Wildfire Smoke
Transport pathways operate across multiple scales. Gautam et al. (2011) documented pre -monsoon aerosol accumulation from the
IGP toward the southern Himalayan slopes, and Duchi et al. (2011) demonstrated synoptic dust transport to the high Himalaya.
Rupakheti et al. (2018) further compared optical properties at foothill sites, supporting strong source and elevation contrasts.
Together with recent Kathmandu, Rara and regional analyses, these studies indicate that “transboundary” should not be treated as a
single source category: Nepal receives anthropogenic haze, mineral dust, and fire smoke through different pathways and at different
altitudes.
The supplied literature also includes cryosphere -focused and atmospheric-chemistry extensions. Bhattarai et al. (2019) developed
an empirical approach for estimating AOD over the Nepalese cryosphere where satellite retrieval is difficult, while Shrestha et al.
(2025b) examined aerosol–ozone relationships over Langtang National Park. These studies are not direct PM2.5 health assessments,
but they demonstrate that aerosol pollution interacts with radiation, trace gases and high-elevation environments in ways that matter
for Himalayan climate and ecosystem exposure.
A central conclusion of the combined literature is that Nepal's aerosol burden cannot be managed as a purely local problem. R egmi
et al. (2020) used back trajectories and fire information to identify mixed transboundary aerosol over Pokhara. Kafle et al. (2025)
combined Kathmandu PM2.5, Indian monitoring data, AOD, fire information, HYSPLIT trajectories, PSCF, and CWT analyses and
found evidence for important transboundary and regional source contributions. Ramachandran and Rupakheti (2026) place these
findings in a broader IGP–Himalaya framework, showing that the foothills are embedded in a regional aerosol system with strong
seasonal exchange.
Western Nepal provides particularly clear evidence of transported fire pollution. Maharjan et al. (2026) analyzed Rara National Park
measurements and reported that regional forest-fire activity explained a large fraction of PM2.5 variability during polluted periods,
with southern and southwesterly air masses linked to elevated concentrations. This finding is significant because Rara lacks the
dense local urban sources of Kathmandu. Elevated PM2.5 there therefore provides a natural demonstration of how regional transport
can degrade air quality far from major cities.
The public-health consequence of wildfire transport is illustrated by Kuikel et al. (2025), who identified hundreds of wildfire-smoke
days in Kathmandu Valley over 2003–2023 and linked smoke episodes to persistent air-quality degradation. Their mortality analysis
indicates that rapid population growth greatly increased the number of people exposed to the hazard over time. Thus, even wit hout
a strong long -term increase in measured PM2.5, population expansion can sharply increase total health burden. This dis tinction
between concentration trend and burden trend is crucial for policy evaluation.

EXPOSURE AND HEALTH CONSEQUENCES
Modeled Mortality and Burden
Tuladhar et al. (2021) coupled WRF-Chem PM2.5 fields with a health -impact model for Kathmandu Valley. Their December 2019
analysis estimated substantial mortality attributable to PM2.5 and showed that a hypothetical 50% concentration reduction wou ld
markedly reduce monthly mortality. Although model -based estimates depend on concentration fields, exposure assumptions, and
concentration– response functions, the study provides a clear demonstration of the potential health benefit of emission reduction.
More recent burden -of-disease work broadens this picture. Adhikari et al. (2026) used government monitoring data and an
environmental burden framework to estimate mortality, disability -adjusted life years, and economic costs attributable to long -term
ambient PM2.5 in Kathmandu Valley. The study translates air pollution from an environmental indicator into a development and
economic issue. Joshi et al. (2026), reviewing Nepal's health evidence, similarly emphasizes respiratory and cardiovascular impacts,
vulnerable populations, and persistent gaps in policy implementation.
Personal Exposure and Vulnerable Groups
Ambient concentration is only one component of dose. Carson et al. (2026) assessed personal PM2.5 exposure among children in
Kathmandu and Bandung, demonstrating the feasibility and importance of personal monitoring in settings where children move
among home, school, travel, and outdoor microenvironments. Such measurements can reveal exposure patterns that fixed monitors
cannot capture. In Kathmandu, this need is reinforced by the in-vehicle findings of Dhital et al. (2014), which show that commuters
can encounter concentrated traffic-related pollution during daily travel.

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
854 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
The evidence therefore supports a shift from a monitor -centered to an exposure -centered framework. Protecting health requires
identifying where high concentrations overlap with large populations, susceptible groups, and high-exposure activities. Schools near
traffic corridors, public-transport users, outdoor workers, households using solid fuels, and communities near brick kilns or waste -
burning areas deserve targeted study and intervention. The supplied literature strongly establishes hazard and burden, but Nepal still
lacks enough longitudinal epidemiology to quantify source-specific risks across diverse populations.
Integrated Synthesis: What the Studies Show Together
The expanded archive sharpens this conceptual model in three ways. First, the aerosol problem has a vertical structure: pollu tants
are concentrated in inhabited valleys but can be lofted and transported into the free troposphere and high Himalaya. Second, aerosol
is both an air-quality and climate-forcing agent; optical absorption, scattering and radiative forcing link source control to regional
climate cobenefits. Third, observational coverage remains geographically uneven. Kathmandu has the strongest chemical and health
evidence, whereas the Terai, eastern Nepal and high mountains rely more heavily on optical, satellite or short-duration observations.
These asymmetries should guide the next generation of monitoring and study design.
Taken together, the comprehensive body of literature reviewed here supports a coherent conceptual model. First, local combust ion
and dust sources establish a high aerosol baseline in urban valleys. Traffic, brick kilns, biomass burning, garbage burning, cooking,
industrial activity, construction, and road dust appear repeatedly across independent methods. Second, atmospheric chemistry
transforms a substantial portion of emitted gases and primary particles into secondary aerosol, so primary -emission inventor ies
alone do not fully explain observed aerosol loading. Third, topography and meteorology determine whether these emissions disperse,
remain trapped, absorb water, or are removed by precipitation. Fourth, regional transport adds pollution from the Indo -Gangetic
Plain and seasonal fires, extending the problem into cleaner and remote regions. Together, these processes explain much of th e
observed spatial and seasonal variability of AOD over Nepal, while surface PM and exposure evidence clarifies the implications of
this columnar aerosol burden for air quality and health.
The agreement among optical, surface, chemical, satellite, trajectory, and modeling studies is stronger than any single datas et.
AERONET establishes robust seasonal column loading; surface monitors confirm that people experience corresponding fine-particle
episodes; chemistry identifies source mixtures; trajectories and fire data demonstrate regional transport; and health models quantify
consequences. Where findings differ—for example, the exact month of maximum AOD in Lumbini or the sign of simple humidity
correlations—the differences are scientifically plausible because aerosol – meteorology relationships depend on rainfall timing,
hygroscopic growth, source activity, vertical distribution, and the specific observation period. These differences should be
interpreted as context dependence, not contradiction.

Evidence Gaps and Methodological Limitations

Figure 4. | Evidence-to-action roadmap. Strong observational foundations now need to be connected through harmonized
monitoring, year-round chemistry, vertical profiling, causal health studies and intervention evaluation.

The largest geographic limitation is the concentration of chemically detailed research in Kathmandu Valley. Pokhara and Lumbi ni
have valuable optical and routine PM observations, but far fewer longterm measurements of composition, black carbon, secondar y
inorganic aerosol, organic aerosol factors, and source -specific tracers. Remote Himalayan evidence is also sparse relative to the
importance of cryosphere and ecosystem exposure.

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
855 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
A second limitation is cross -study comparability. The literature uses AOD, PM1, PM2.5, PM10, optical parameters, satellite
products, low-cost sensors, reference monitors, filter chemistry, and models across different periods. These metrics describe related
but nonidentical parts of the aerosol system. Future work should colocate surface PM, AERONET, lidar or vertical -profile
measurements, meteorology, and chemical speciation so that column-to-surface relationships can be quantified rather than assumed.
Third, source apportionment is strongest during intensive campaigns rather than across full annual cycles. Kathmandu source
contributions measured during pre -monsoon or winter cannot automatically be generalized to monsoon and post -monsoon
conditions. Year-round chemically resolved monitoring is needed to distinguish persistent sources from seasonal sources and to
evaluate policy changes.
Fourth, health evidence is developing but remains less mature than the atmospheric evidence. Burden models demonstrate substantial
impacts, yet Nepal needs more cohort, time -series, birth -outcome, childhealth, cardiovascular, respiratory, and source -specific
epidemiological studies. Personal exposure, indoor –outdoor exchange, occupation, transport mode, socioeconomic vulnerability,
and household energy use should be integrated into future health designs.
Finally, transboundary attribution remains inherently uncertain. Back trajectories, PSCF/CWT, satellite AOD, and fire detecti ons
identify likely source regions, but quantitative separation of local versus imported PM requires chemically constrained regio nal
modeling, receptor modeling, and coordinated measurements across Nepal and neighboring countries. Research Priorities
• Establish a harmonized national aerosol network linking reference PM2.5/PM10 monitors with calibrated low -cost sensors,
AERONET, meteorology, and periodic chemical speciation.
• Expand year -round source -apportionment measurements beyond Kathmandu to Pokhara, Lumbini, the Terai, and remote
Himalayan sites.
• Develop Nepal -specific, frequently updated emission inventories for vehicles, brick kilns, industry, open waste burning,
household combustion, road dust, and fires.
• Integrate boundary-layer observations and meteorological forecasting into operational air -quality alerts, especially for winter
stagnation and pre-monsoon fire episodes.
• Quantify transboundary contributions with coordinated regional observations and chemically evaluated transport models.
• Prioritize personal-exposure and epidemiological studies in children, commuters, outdoor workers, kiln-adjacent communities,
and other high-exposure groups.
• Evaluate interventions with before –after designs so that changes in emissions, concentrations, exposure, and health outcomes
can be linked directly.
Policy Implications
The literature points toward a multi -source strategy rather than a single intervention. Cleaner and bettermaintained vehicle fleets,
inspection and maintenance, public transport modernization, road -dust control, construction management, cleaner brick -kiln
technologies and fuels, elimination of open garbage burning, improved household energy, and fire prevention all have defensib le
roles. Because secondary aerosol is substantial, controls on gaseous precursors must accompany direct particle controls. Beca use
regional transport is important, Nepal also benefits from South Asian cooperation on agricultural burning, wildfire smoke, industrial
emissions, and shared forecasting.
Policy timing matters. Winter stagnation and pre-monsoon fire periods should trigger stronger shortterm protection measures, while
the monsoon provides a useful natural contrast for evaluating source strength. Public advisories should be linked to health -relevant
PM2.5 rather than visibility alone, and vulnerable groups should receive specific guidance during high -pollution episodes.
Monitoring should be designed not merely to report AQI but to evaluate whether policies reduce population -weighted exposure.

Cross-domain evidence synthesis
Table 1. | Cross-domain synthesis of the supplied evidence base. The table emphasizes convergence across methods and the
most important unresolved gaps.
Evidence domain Strongest locations Main signal Key methods Priority gap
Optical climatology Pokhara,
Lumbini,
Kathmandu, high
Himalaya
Premonsoon/winter
enhancement;
monsoon minimum
AERONET, sun
photometry, satellite
AOD
Long, harmonized
multi-site records
Surface PM Kathmandu, Pokhara,
Rara
Strong urban – remote
and
seasonal contrasts
Reference/lowcost PM
sensors
National calibration
and coverage

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
856 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
Chemical sources Kathmandu
Valley
Traffic, biomass/trash
burning, kilns, dust,
secondary
aerosol
AMS, filter
chemistry,
PMF/CMB
Year-round chemistry
outside
Kathmandu
Vertical/radiative Pokhara,
Kathmandu,
Yala/high
Himalaya
Strong lower-
atmosphere
gradients;
absorption and
forcing
Aircraft, radiometers,
optical retrievals
Co-located vertical
profiles and
chemistry
Regional transport IGP–foothills,
Kathmandu, Rara,
NCO-P
Anthropogenic haze,
fires and
dust reach
remote/elevated sites
HYSPLIT,
PSCF/CWT,
satellite/fire data
Quantitative local -vs-
imported attribution
Exposure/health Kathmandu
Valley
High personal
exposure; mortality,
DALY and economic
burden
Personal
monitors, WRFChem,
burden
models
Cohort/timeseries and
sourcespecific
epidemiology

CONCLUSION
The complete body of supplied literature shows that aerosol pollution in Nepal is a coupled local– regional atmospheric and public-
health problem. Kathmandu V alley experiences the most intensively documented burden, driven by traffic, brick kilns, biomass and
garbage burning, dust, and secondary aerosol formation under meteorological conditions that often suppress dispersion. Pokhar a
and Lumbini show strong seasonal aerosol loading and clear influence from fires, anthropogenic emissions, rainfall, and regio nal
transport. Remote and high-elevation sites are cleaner on average but remain vulnerable to transported pollution, particularly during
regional fire episodes.
The strongest scientific conclusion is not a single concentration value or source percentage, but the convergence of multiple methods.
Optical observations, surface PM measurements, chemical source apportionment, satellite data, trajectory analysis, atmosp heric
modeling, personal monitoring, and health -burden studies all point toward the same need: integrated control of local emissions,
improved regional cooperation, meteorology -aware management, and a stronger exposure and health surveillance system. Futur e
research should move from isolated campaigns toward coordinated long -term observations that connect emissions to atmospheric
transformation, population exposure, and measurable health benefits. Such an approach would provide Nepal with the evidence
needed to shift from describing severe air pollution to demonstrating which interventions deliver the largest and most equitable
improvements.

REFERENCES

1. Acharya, A., Adhikari, B., Bhattarai, P., Jha, G., Acharya, S., & Shah, R. (2020). Spectral analysis of aerosol optical depth
   over AERONET sites of Nepal. BIBECHANA, 17, 80–88. https://doi.org/10.3126/bibechana.v17i0.26507
2. Adhikari, S., Rattanapan, C., Laosee, O., Thapa, S., Acharya, S. R., Saud, B., Sriram, S., & Bhatta, J. (2026). Health and
   economic costs attributable to ambient air pollution levels in the Kathmandu Valley, Nepal. Discover Public Health, 23,

729. https://doi.org/10.1186/s12982-026-02083-x

3. Bhattarai, B. C., Burkhart, J. F., Stordal, F., & Xu, C.-Y . (2019). Aerosol optical depth over the Nepalese cryosphere derived
   from an empirical model. Frontiers in Earth Science, 7, 178. https://doi.org/10.3389/feart.2019.00178
4. Carrico, C. M., Bergin, M. H., Shrestha, A. B., Dibb, J. E., Gomes, L., & Harris, J. M. (2003). The importance of carbon
   and mineral dust to seasonal aerosol properties in the Nepal Himalaya. Atmospheric Environment, 37, 2811 – 2824.
   https://doi.org/10.1016/S1352-2310(03)00197-3
5. Carson, F. S., Horwell, C. J., Iqbal, M., Shahi, K., Bhandari, R., Sofyan, A., Santoso, D., Dhimal, M., Oginawati, K.,
   Mueller, W., Loh, M., & Galea, K. S. (2026). Assessment of personal PM2.5 exposure of children living in Bandung,
   Indonesia and Kathmandu , Nepal. Environmental Research: Health. Advance online publication.
   https://doi.org/10.1088/2752-5309/ae8050
6. Chalise, R., Sharma, S., Chalise, B., Chalise, L. P., & Yadav, S. N. (2025). Seasonal variation of PM2.5 and PM10 in urban
   and remote regions of Nepal. Himalayan Physics, 12(1), 41–50. https://doi.org/10.3126/hp.v12i1.82150
7. Cho, C., Kim, S. -W., Rupakheti, M., Park, J. -S., Panday, A., Yoon, S. -C., et al. (2017). Wintertime aerosol optical and
   radiative properties in the Kathmandu Valley during the SusKat-ABC field campaign. Atmospheric Chemistry and Physics,
   17, 12617–12632. https://doi.org/10.5194/acp-17-12617-2017

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
857 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
8) Dahal, S., Bhattarai, B. K., Rupakheti, D., Shrestha, J. K., & Sharma, R. K. (2022a). Festival induced air quality
perturbation over an urban center in eastern Nepal. Journal of Lumbini Engineering College, 4(1), 1 –6.
https://doi.org/10.3126/lecj.v4i1.49358
9) Dahal, S., Rupakheti, D., Sharma, R. K., Bhattarai, B. K., & Adhikary, B. (2022b). Aerosols over the foothills of the Eastern
Himalayan region during post -monsoon and winter seasons. Aerosol and Air Quality Research.
https://doi.org/10.4209/aaqr.210152
10) Dhital, N. B., Hung, W. T., & Byanju, R. M. (2014). Air pollution inside public transport vehicles of Kathmandu Valley.
Nepal Journal of Environmental Science, 2, 35–41.
11) Duchi, R., Cristofanelli, P., Marinoni, A., Laj, P., Marcq, S., Villani, P., et al. (2011). Continuous observations of synoptic-
scale dust transport at the Nepal Climate Observatory -Pyramid (5079 m a.s.l.) in the Himalayas. Atmospheric Chemistry
and Physics Discussions, 11, 4229–4261. https://doi.org/10.5194/acpd-11-4229-2011
12) Gautam, R., Hsu, N. C., Tsay, S. C., Lau, K. M., Holben, B., Bell, S., et al. (2011). Accumulation of aerosols over the Indo-
Gangetic plains and southern slopes of the Himalayas: distribution, properties and radiative effects during the 2009 pre -
monsoon season. Atmospheric Chemistry and Physics, 11, 12841–12863. https://doi.org/10.5194/acp-1112841-2011
13) Islam, M. R., Jayarathne, T., Simpson, I. J., Werden, B., Maben, J., Gilbert, A., Praveen, P. S., Adhikari, S., Panday, A. K.,
Rupakheti, M., Blake, D. R., Yokelson, R. J., DeCarlo, P. F., Keene, W. C., & Stone, E. A. (2020). Ambient air quality in
the Kathmandu Valley, Nepal, during the pre-monsoon: Concentrations and sources of particulate matter and trace gases.
Atmospheric Chemistry and Physics, 20, 2927–2951. https://doi.org/10.5194/acp-20-29272020
14) Islam, M. R., Li, T., Mahata, K., Khanal, N., Werden, B., Giordano, M. R., Puppala, S. P., Dhital, N. B., Gurung, A.,
Saikawa, E., Panday, A. K., Yokelson, R. J., DeCarlo, P. F., & Stone, E. A. (2022). Wintertime air quality across the
Kathmandu Valley, Nepal: Concentration, composition, and sources of fine and coarse particulate matter. ACS Earth and
Space Chemistry, 6, 2955–2971. https://doi.org/10.1021/acsearthspacechem.2c00243
15) Jha, R., Adhikari, B., & Singh, D. K. (2021). Study of aerosol optical properties at different tourist places of Nepal.
BIBECHANA, 18(1), 170–183. https://doi.org/10.3126/bibechana.v18i1.29906
16) Joshi, P. R., Khadka, K., & Karki, T. B. (2026). A review of the health burden associated with air pollution exposure in
Nepal. NPRC Journal of Multidisciplinary Research, 3(3), 206–215. https://doi.org/10.3126/nprcjmr.v3i3.92483
17) Kafle, H., Kafle, K., Bhujel, S., Thapa, G., Khadgi, J., & Cohen, D. D. (2025). Influence of transboundary air pollution
into the atmosphere of Kathmandu Valley. APN Science Bulletin, 15(1), 164–182. https://doi.org/10.30852/sb.2025.3056
18) Kuikel, S., Paudel, H. K., Kuinkel, D., Joshi, K. P., Sapkota, S., Malakar, N., Wang, S.-Y . S., & Pokharel, B. (2025). Impact
of wildfire smoke on air pollution -related premature mortality in rapidly growing Kathmandu Valley. Atmospheric
Environment: X, 26, 100334. https://doi.org/10.1016/j.aeaoa.2025.100334
19) Lamichhane, G. P ., Maharjan, N., & Timalsina, N. (2026). Integrating satellite AOD, trace gases, and meteorological
reanalysis to estimate PM2.5 and its long-term trends in southern Nepal. Environmental Monitoring and Assessment, 198,
750. https://doi.org/10.1007/s10661-026-15551-3
20) Maharjan, N., Lamichhane, G. P., Timalsina, N., Paudel, S. P., & Sapkota, R. P. (2026). Long -range transport, regional
forest fire events and meteorological influences on PM2.5 in Western Nepal. The Geographical Journal of Nepal, 19, 1 –
22. https://doi.org/10.3126/gjn.v19i1.92139
21) Pandey, S., Basnet, K., Subedi, P., Subedi, A., & Sapkota, S. (2024). Study and comparison of air pollution in three stations
of Pokhara Valley. Himalayan Physics, 11(1), 78–91. https://doi.org/10.3126/hp.v11i1.69937
22) Rai, M., Mahapatra, P. S., Gul, C., Kayastha, R. B., Panday, A. K., & Puppala, S. P . (2019). Aerosol radiative forcing
estimation over a remote high-altitude location (~4900 masl) near Yala Glacier, Nepal. Aerosol and Air Quality Research,
19, 1872–1891. https://doi.org/10.4209/aaqr.2018.09.0342
23) Ramachandran, S., & Rupakheti, M. (2021). Inter-annual and seasonal variations in optical and physical characteristics of
columnar aerosols over the Pokhara Valley in the Himalayan foothills. Atmospheric Research, 248, 105254.
https://doi.org/10.1016/j.atmosres.2020.105254
24) Ramachandran, S., & Rupakheti, M. (2026). Aerosol pollution across the Indo-Gangetic Plain and the Himalayas: Seasonal
patterns and implications for air quality and climate. Air Quality, Atmosphere & Health, 19, 42.
https://doi.org/10.1007/s11869-026-01897-7
25) Ramachandran, S., & Rupakheti, M. (2026b). Composition and radiative forcing of aerosols across the Indo-Gangetic Plain
and Himalayas: A seasonal analysis. Atmospheric Environment: X, 30,
100433. https://doi.org/10.1016/j.aeaoa.2026.100433
26) Ramachandran, S., Rupakheti, M., Cherian, R., & Lawrence, M. G. (2023). Aerosols heat up the Himalayan climate.
Science of the Total Environment, 894, 164733. https://doi.org/10.1016/j.scitotenv.2023.164733

Aerosol Optical Depth Over Nepal: A Comprehensive Review of Spatial and Seasonal Variability, Sources,
Meteorological Controls, Regional Trasport, and Implications
858 Volume 03 Issue 10 October 2026 Corresponding Author: Kailash Basnet
27) Regmi, J., Poudyal, K. N., Pokhrel, A., Gyawali, M., Tripathee, L., Panday, A., Barinelli, A., & Aryal, R. (2020).
Investigation of aerosol climatology and long -range transport of aerosols over Pokhara, Nepal. Atmosphere, 11, 874.
https://doi.org/10.3390/atmos11080874
28) Regmi, J., Poudyal, K. N., Pokhrel, A., Malakar, N., Gyawali, M., Tripathee, L., Rai, M., Ramachandran, S., Wilson, K.,
& Aryal, R. (2023). Analysis of surface level PM2.5 measured by low-cost sensor and satellite-based column aerosol optical
depth (AOD) over Kathmandu. Aerosol and Air Quality Research, 23, 220311. https://doi.org/10.4209/aaqr.220311
29) Rijal, S., Adhikari, G. P., Basnet, N., Shrestha, P. M., Khatri, K., Tiwari, B. R., & Poudyal, K. N. (2025). Exploring aerosol
optical depth: Unveiling meteorological impacts over Lumbini, Nepal. Scientific World, 18(18), 18 –26.
https://doi.org/10.3126/sw.v18i18.78754
30) Rupakheti, D., Kang, S., Cong, Z., Rupakheti, M., Tripathee, L., Panday, A. K., & Holben, B. (2018). Study of aerosol
optical properties over two sites in the foothills of the central Himalayas. International Archives of the Photogrammetry,
Remote Sensing and Spatial Information Sciences, XLII -3, 1493 –1498. https://doi.org/10.5194/isprs -archives-XLII-3-
1493-2018
31) Sapkota, S., Gautam, S., Gautam, A., & Ale, B. (2023c). Correlative study of aerosol optical depth with precipitable water
over five AERONET stations worldwide. BIBECHANA, 20(3), 213–223. https://doi.org/10.3126/bibechana.v20i3.57153
32) Sapkota, S., Gautam, S., Gautam, A., Poudel, R., Pokheral, S., Basnet, K., & Subedi, A. (2023b). Comparison of aerosol
optical properties over Lumbini, Pokhara and Langtang-Base Camp. Himalayan Physics, 10(1), 58–65.
33) Sapkota, S., Gautam, S., Pokhrel, S., Gautam, A., Basnet, K., Mishra, R. K., & Regmi, J. (2023a). Study of aerosol optical
properties in Lumbini, Nepal. BIBECHANA, 20(1), 1–9. https://doi.org/10.3126/bibechana.v20i1.48825
34) Shrestha, D., Chand, A., Thapa, P., & Ojha, B. (2025). Assessing the spatial variation of aerosol optical depth and its
relationship with land use/land cover in Kathmandu Valley, Nepal. Journal of Land Management and Geomatics Education,
7, 8–14.
35) Shrestha, P. M., Gupta, S. P., Rai, K. B., Joshi, U., Chapagain, N. P., Karki, I. B., & Poudyal, K. N. (2025b). Impact of
aerosol on atmospheric ozone over Langtang National Park, Nepal. Journal of Indigenous Knowledge and Practice, 1(1),
83–95.
36) Shrestha, P. M., Joshi, U., Chapagain, N. P., Karki, I. B., & Poudyal, K. N. (2015). Study of variation of aerosols on high
mountain, Jomsom. [Study supplied in review archive].
37) Singh, A., Mahata, K. S., Rupakheti, M., Junkermann, W., Panday, A. K., & Lawrence, M. G. (2019). An overview of
airborne measurement in Nepal – Part 1: Vertical profile of aerosol size, number, spectral absorption, and meteorology.
Atmospheric Chemistry and Physics, 19, 245–258. https://doi.org/10.5194/acp-19-245-2019
38) Telee, L. B. S., Yadav, U. K., & Kumar, A. (2026). Air quality and meteorological drivers in Kathmandu Valley, Nepal: A
2021–2023 observational study. Explora: Environment and Resource. Advance online publication.
https://doi.org/10.36922/EER025490086
39) Thapa, M. K., Bhattarai, B. K., Gurung, S., Sapkota, B. K., Poudyal, K. N., & Karki, N. R. (2017). Effects of aerosols on
the solar radiation in mid -hill of Nepal: a case study in the Kathmandu Valley. International Journal of System Assurance
Engineering and Management, 8, 54–62. https://doi.org/10.1007/s13198-016-0527-y
40) Tuladhar, A., Manandhar, P., & Shrestha, K. L. (2021). Assessment of health impact of PM2.5 exposure by using WRF -
Chem model in Kathmandu Valley, Nepal. Frontiers in Sustainable Cities, 3, 672428.
https://doi.org/10.3389/frsc.2021.672428
41) Werden, B. S. (2021). Chemical source apportionment of ambient particulate matter in the Kathmandu Valley, Nepal
[Doctoral dissertation, Drexel University]. https://doi.org/10.17918/00000361
42) Werden, B. S., Giordano, M. R., Goetz, J. D., Islam, M. R., Bhave, P. V ., Puppala, S. P., Rupakheti, M., Saikawa, E., Panday,
A. K., Yokelson, R. J., Stone, E. A., & DeCarlo, P. F. (2022). Pre -monsoon submicron aerosol composition and source
contribution i n the Kathmandu Valley, Nepal. Environmental Science: Atmospheres, 2, 978 –996.
https://doi.org/10.1039/d2ea00008c
43) Werden, B. S., Giordano, M. R., Mahata, K., Islam, M. R., Goetz, J. D., Puppala, S. P., Saikawa, E., Panday, A. K., Yokelson,
R. J., Stone, E. A., & DeCarlo, P. F. (2023). Submicron aerosol composition and source contribution across the Kathmandu
Valley, Nepal, in winter. ACS Earth and Space Chemistry, 7, 49–68. https://doi.org/10.1021/acsearthspacechem.2c00226
44) Zhong, M., Saikawa, E., Avramov, A., Chen, C., Sun, B., Ye, W., Keene, W. C., Yokelson, R. J., Jayarathne, T., Stone, E.
A., Rupakheti, M., & Panday, A. K. (2019). Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE):
Emissions of particulate m atter and sulfur dioxide from vehicles and brick kilns and their impacts on air quality in the
Kathmandu Valley, Nepal. Atmospheric Chemistry and Physics, 19, 8209–8228. https://doi.org/10.5194/acp-19-8209-2019