Seasonal Variation and Sources of Carbonaceous Species and Elements in PM2.5 and PM10 Over the Eastern Himalaya

Abstract The study represents the seasonal characteristics (carbonaceous aerosols and elements) and contribution of prominent sources PM2.5 and PM10 in the high altitude of the eastern Himalaya (Darjeeling) during August 2018-July 2019. Carbonaceous aerosols [organic carbon (OC), elemental carbon (EC) and water soluble organic carbon (WSOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Cr, Ni, Mo, Cl, P, S, K, Zr, Pb, Na, Mg, Ca, and B) in PM2.5 and PM10 were analyzed to estimate their possible sources. The annual average concentration of PM2.5 and PM10 were computed as 37±12 µg m-3 and 58±18 µg m-3, respectively. In the present case, total carbonaceous species in PM2.5 and PM10 were accounted for 20.6% of PM2.5 and 18.6% of PM10, respectively. Whereas, trace elements in PM2.5 and PM10 were estimated as 15% of PM2.5 and 12% of PM10, respectively. Monthly are seasonal variations in concentrations of carbonaceous aerosols and elements in PM2.5 and PM10 were also observed during the observational period. The positive relationship between OC & EC and OC & WSOC of PM2.5 and PM10 during all the seasons (except monsoon in case of PM10) indicate rheir common sources. The enrichment factors (EFs) and significant positive correlation of Al with othe crustal elements (Fe, Ca, Mg and Ti) of fine and coarse mode aerosols indicates the influence of mineral dust at the Darjeeling. Principal component analysis (PCA) resolved the four common sources (biomass burning + fossil fuel combustion (BB+FFC), crustal/soil dust, vehicular emissions (VE) and industrial emissions (IE)) of PM2.5 and PM10 in Darjeeling.

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Source and Source Region of Carbonaceous Species and Trace Elements in PM10 over Delhi, India

Environmental Sciences Proceedings ◽

10.3390/ecas2021-10346 ◽

2021 ◽

Vol 8 (1) ◽

pp. 2

Author(s):

Rubiya Banoo ◽

Sudhir Kumar Sharma ◽

Martina Rani ◽

Tuhin Kumar Mandal

Keyword(s):

Trace Elements ◽

Organic Carbon ◽

Source Region ◽

Sampling Site ◽

Water Soluble ◽

Local Source ◽

Residential Areas ◽

Industrial Emissions ◽

Carbonaceous Species ◽

Potential Source

This study investigated the carbonaceous species [elemental carbon (EC), organic carbon (OC), water soluble organic carbon (WSOC)] along with the trace elements (Al, S, Ti, Mn, Fe, Cu, Zn, As, Br, Pb, Cr, F, Cl, Na, K, Mg, Ca, P) in PM10 over the megacity Delhi, India (collected from 2015–2019) to address certain significant scientific issues (i.e., what are the directionality or pathway of these emissions; what are the possible emission sources which are distressing the observation site; what are the periodical variations in these emissions; and whether the emissions are local, regional, or trans-boundary). Integration of these problems are addressed using various statistical approaches including potential source areas (PSA) [using hybrid modelling i.e., potential source contribution factor (PSCF)], the conditional bivariate probability function (CBPF), and principal component analysis (PCA). Furthermore, seasonal PSCF and CBPF indicate both local source (highly polluted residential areas, traffic congestions, and industrial emissions) and regional sources (Haryana, Punjab) dominancy during winter and post-monsoon seasons at the receptor site, whereas during summer and monsoon along with local source and the regional, trans-boundaries (Indo-Gangatic plane, Pakistan, Afghanistan, and Bay of Bengal) air parcel patterns also contribute to the aerosol loading at the sites. Moreover, the PCA approach framed four common sources [crustal/road dust (RD), industrial emission (IE), fossil fuel combustion + biomass burning (FCC+ BB), vehicular emission (VE)] with one mixed source over the sampling site of Delhi.

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Characteristics, seasonality and sources of carbonaceous and ionic components in the tropical Indian aerosols

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-3937-2011 ◽

2011 ◽

Vol 11 (2) ◽

pp. 3937-3976 ◽

Cited By ~ 1

Author(s):

C. M. Pavuluri ◽

K. Kawamura ◽

S. G. Aggarwal ◽

T. Swaminathan

Keyword(s):

Organic Carbon ◽

Atmospheric Aerosols ◽

Atmospheric Transport ◽

Indian Subcontinent ◽

Ionic Species ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Mass Fractions ◽

High Concentrations ◽

Ionic Components

Abstract. To better characterize South and Southeast Asian aerosols, PM10 samples collected from tropical Chennai, India (13.04° N; 80.17° E) were analyzed for carbonaceous and water-soluble ionic components. Concentration ranges of elemental carbon (EC) and organic carbon (OC) were 2.4–14 μg m−3 and 3.2–15.6 μg m−3 in winter samples whereas they were 1.1–2.5 μg m−3 and 4.1–17.6 μg m−3 in summer samples, respectively. Concentration of secondary organic carbon (SOC) retrieved from EC-tracer method was 4.6 ± 2.8 μg m−3 in winter and 4.3 ± 2.8 μg m−3 in summer. SO42- (8.8 ± 2.5 μg m−3 and 4.1 ± 2.7 μg m−3 in winter and summer, respectively) was found as the most abundant ionic species (57% on average, n = 49), followed by NH4+ (15%) > NO3− > Cl− > K+> Na+ > Ca2+ > MSA− > Mg2+. The mass fractions of EC, organic matter (OM) and ionic species varied seasonally, following the air mass trajectories and corresponding source strength. Based on mass concentration ratios of selected components and relations of EC and OC to marker species, we found that biofuel/biomass burning is the major source of atmospheric aerosols in South and Southeast Asia. The high concentrations of SOC and WSOC/OC ratios (ave. 0.45; n = 49) as well as good correlations between SOC and WSOC suggest that the secondary production of organic aerosols during long-range atmospheric transport is also significant in this region. This study provides the baseline data of carbonaceous aerosols for southern part of the Indian subcontinent.

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Investigation of atmospheric aerosols over semi-urban and urban areas in Eastern Indo-Gangetic Plain: seasonal variability and source apportionment using PMF

10.5194/egusphere-egu21-14205 ◽

2021 ◽

Author(s):

Kanishtha Dubey ◽

Shubha Verma

Keyword(s):

Organic Carbon ◽

Biomass Burning ◽

Atmospheric Aerosols ◽

Urban Areas ◽

Relative Concentration ◽

Road Dust ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Gangetic Plain ◽

Brick Kilns

The study investigates the chemical composition and source of aerosol origin at a semi-urban (Kharagpur&#8211;Kgp) and urban (Kolkata&#8211;Kol) region during the period February 2015 to January 2016 and September 2010 to August 2011 respectively. Major water-soluble inorganic aerosols (WSII) were determined using Ion chromatography and carbonaceous aerosols (CA) using OC&#8211;EC analyser. A multivariate factor analysis Positive Matrix Factorization (PMF) was used in resolving source of aerosols at the study locations. Seasonal analysis of WSII at Kgp and Kol indicated relative dominance of calcium at both the places followed by sodium, chloride, and magnesium ions. Non-sea salt potassium (nss&#8211;K+), a biomass burning tracer was found higher at Kol than at Kgp. Sum of secondary aerosols sulphate (SO42-), nitrate (NO3-) and ammonium (NH4+) was higher at Kol than Kgp with relative concentration of SO42- being higher than NO3- at Kgp which was vice-versa at Kol. Examination of carbonaceous aerosols showed three times higher concentration of organic carbon (OC) than elemental carbon (EC) with monthly mean of OC/EC ratio > 2, indicating likely formation of secondary organic carbon formation. Seasonal influence of biomass burning inferred from nss&#8211;K+ (OC/EC) ratio relationship indicated dissimilarity in seasonality of biomass burning at Kgp (Kol). PMF resolved sources for Kgp constituted of secondary aerosol emissions, biomass burning, fugitive dust, marine aerosols, crustal dust and emissions from brick kilns while for Kol factors constituted of burning of waste, resuspended paved road dust, coal combustion, sea spray aerosols, vehicular emissions and biomass burning.

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Fossil vs. non-fossil sources of fine carbonaceous aerosols in four Chinese cities during the extreme winter haze episode of 2013

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-1299-2015 ◽

2015 ◽

Vol 15 (3) ◽

pp. 1299-1312 ◽

Cited By ~ 113

Author(s):

Y.-L. Zhang ◽

R.-J. Huang ◽

I. El Haddad ◽

K.-F. Ho ◽

J.-J. Cao ◽

...

Keyword(s):

Particulate Matter ◽

Organic Carbon ◽

Biomass Burning ◽

Water Soluble ◽

Total Carbon ◽

World Health ◽

Biomass Combustion ◽

Carbonaceous Aerosols ◽

Haze Episode ◽

Mass Concentrations

Abstract. During winter 2013, extremely high concentrations (i.e., 4–20 times higher than the World Health Organization guideline) of PM2.5 (particulate matter with an aerodynamic diameter < 2.5 μm) mass concentrations (24 h samples) were found in four major cities in China including Xi'an, Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data set from elemental carbon (EC), organic carbon (OC), 14C and biomass-burning marker measurements using Latin hypercube sampling allowed a quantitative source apportionment of carbonaceous aerosols. Based on 14C measurements of EC fractions (six samples each city), we found that fossil emissions from coal combustion and vehicle exhaust dominated EC with a mean contribution of 75 ± 8% across all sites. The remaining 25 ± 8% was exclusively attributed to biomass combustion, consistent with the measurements of biomass-burning markers such as anhydrosugars (levoglucosan and mannosan) and water-soluble potassium (K+). With a combination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China is suggested to be combustion of crop residues. The contribution of fossil sources to OC was highest in Beijing (58 ± 5%) and decreased from Shanghai (49 ± 2%) to Xi'an (38 ± 3%) and Guangzhou (35 ± 7%). Generally, a larger fraction of fossil OC was from secondary origins than primary sources for all sites. Non-fossil sources accounted on average for 55 ± 10 and 48 ± 9% of OC and total carbon (TC), respectively, which suggests that non-fossil emissions were very important contributors of urban carbonaceous aerosols in China. The primary biomass-burning emissions accounted for 40 ± 8, 48 ± 18, 53 ± 4 and 65 ± 26% of non-fossil OC for Xi'an, Beijing, Shanghai and Guangzhou, respectively. Other non-fossil sources excluding primary biomass burning were mainly attributed to formation of secondary organic carbon (SOC) from non-fossil precursors such as biomass-burning emissions. For each site, we also compared samples from moderately to heavily polluted days according to particulate matter mass. Despite a significant increase of the absolute mass concentrations of primary emissions from both fossil and non-fossil sources during the heavily polluted events, their relative contribution to TC was even decreased, whereas the portion of SOC was consistently increased at all sites. This observation indicates that SOC was an important fraction in the increment of carbonaceous aerosols during the haze episode in China.

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Seasonal characteristics of water-soluble organic carbon in atmospheric particles in the inland Kanto plain, Japan

Atmospheric Environment ◽

10.1016/j.atmosenv.2009.04.008 ◽

2009 ◽

Vol 43 (21) ◽

pp. 3345-3351 ◽

Cited By ~ 25

Author(s):

Kimiyo Kumagai ◽

Akihiro Iijima ◽

Hiroshi Tago ◽

Atsushi Tomioka ◽

Kunihisa Kozawa ◽

...

Keyword(s):

Organic Carbon ◽

Atmospheric Particles ◽

Water Soluble ◽

Seasonal Characteristics ◽

Water Soluble Organic Carbon ◽

Soluble Organic Carbon

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Observation and Source Apportionment of Trace Gases, Water-Soluble Ions and Carbonaceous Aerosol During a Haze Episode in Wuhan

Atmosphere ◽

10.3390/atmos10070397 ◽

2019 ◽

Vol 10 (7) ◽

pp. 397 ◽

Cited By ~ 1

Author(s):

Zhengxu Gao ◽

Xiaoling Wang ◽

Lijuan Shen ◽

Hua Xiang ◽

Honglei Wang

Keyword(s):

Organic Carbon ◽

Air Pollutants ◽

Principal Component ◽

Water Soluble ◽

Vehicle Exhaust ◽

Soluble Ions ◽

Secondary Formation ◽

Water Soluble Ions ◽

Haze Episode ◽

Haze Days

As the new core region of the haze pollution, the terrain effect of sub-basin and water networks over the Twin-Hu Basin (THB) in the Yangtze River Middle-Reach (YRMR) had great impacts on the variations and distributions of air pollutants. In this study, trace gases (NH3, HNO3, and HCl), water-soluble ions (WSIs), organic carbon (OC), and elemental carbon (EC) were measured in PM2.5 from 9 January to 27 January 2018, in Wuhan using monitoring for aerosols and gases (MARGA) and a semi-continuous OC/EC analyzer (Model RT-4). The characteristics of air pollutants during a haze episode were discussed, and the PM2.5 sources were quantitatively analyzed on haze and non-haze days using the principal component analysis/absolute principal component scores (PCA/APCS) model. The average PM2.5 concentration was 122.61 μg·m−3 on haze days, which was 2.20 times greater than it was on non-haze days. The concentrations of secondary water soluble ions (WSIs) including NO3−, SO42−, and NH4+ increased sharply on haze days, which accounted for 91.61% of the total WSIs and were 2.43 times larger than the values on non-haze days. The heterogeneous oxidation reactions of NO2 and SO2 during haze episodes were proven to be the major sources of sulfate and nitrate in PM2.5. On haze days, the concentrations of EC, primary organic carbon (POC), and secondary organic carbon (SOC) were 1.68, 1.69, and 1.34 times larger than those on non-haze days, the CO, HNO3, and NH3 concentrations enhanced and relatively low SO2, O3, and HNO2 levels were observed on haze days. The diurnal variations of different pollutants distinctly varied on haze days. The PM2.5 in Wuhan primarily originated from the secondary formation, combustion, dust, industry, and vehicle exhaust sources. The source contributions of the secondary formation + combustion sources to PM2.5 on haze days were 2.79 times larger than the level on non-haze days. The contribution of the vehicle exhaust + combustion source on haze days were 0.59 times the value on non-haze days. This description is supported by a summary of how pollutant concentrations and patterns vary in the THB compared to the variations in other pollution regions in China, which have been more completely described.

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Chemical and optical properties of carbonaceous aerosols in Nanjing, eastern China: regionally transported biomass burning contribution

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-11213-2019 ◽

2019 ◽

Vol 19 (17) ◽

pp. 11213-11233 ◽

Cited By ~ 8

Author(s):

Xiaoyan Liu ◽

Yan-Lin Zhang ◽

Yiran Peng ◽

Lulu Xu ◽

Chunmao Zhu ◽

...

Keyword(s):

Optical Properties ◽

Organic Carbon ◽

Solar Energy ◽

Energy Absorption ◽

Biomass Burning ◽

Eastern China ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Southeastern China ◽

Brown Carbon

Abstract. Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss-K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m−3, 2.1–56.2 ng m−3, 1.4–32.2 ng m−3 and 0.2–3.8 µg m−3, respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev∕man and lev∕nss-K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p < 0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m−2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m−2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m−2, considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere.

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Carbonaceous aerosols on the south edge of the Tibetan Plateau: concentrations, seasonality and sources

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-25051-2014 ◽

2014 ◽

Vol 14 (18) ◽

pp. 25051-25082 ◽

Cited By ~ 5

Author(s):

Z. Cong ◽

S. Kang ◽

K. Kawamura ◽

B. Liu ◽

X. Wan ◽

...

Keyword(s):

Tibetan Plateau ◽

Organic Carbon ◽

Monsoon Season ◽

Air Pollutant ◽

Water Soluble ◽

Atmospheric Environment ◽

The Tibetan Plateau ◽

Carbonaceous Aerosols ◽

The South ◽

Aerosol Composition

Abstract. To quantitatively evaluate the effect of carbonaceous aerosols on the south edge of the Tibetan Plateau, aerosol samples were collected weekly from August 2009 to July 2010 at Mt. Everest (Qomolangma Station for Atmospheric and Environmental Observation and Research, briefly QOMS, 28.36° N, 86.95° E, 4276 m a.s.l.). The samples were analyzed for organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and major ions. The average concentrations of OC, EC and WSOC were 1.43, 0.25 and 0.77 μg m−3, respectively. The concentration levels of OC and EC at QOMS are comparable to those at high elevation sites on the southern slopes of the Himalayas (Langtang and NCO-P), but three to six times lower than those at Manora Peak, India and Godavari, Nepal. Sulfate was the most abundant anion species followed by nitrate, accounting for 25 and 12% of total ionic mass, respectively. Ca2+ was the most abundant cation species (annual average of 0.88 μg m−3). The various aerosol compositions showed distinctive seasonality. The dust loading, represented by Ca2+ concentration, was relatively constant throughout the year. While OC, EC and other ionic species (NH4+, K+, NO3−, and SO42−) exhibited a pronounced peak in the pre-monsoon period and a minimum in the monsoon season. Similar seasonal trends of aerosol composition were also reported previously from the southern slope of the Himalayas, such as Langtang and NCO-P. This phenomenon indicates that both slopes of Himalayas share a common atmospheric environment regime. The strong correlation of OC and EC in QOMS aerosols with K+ and levoglucosan indicates that they were mainly originated from biomass burning. The active fire spots observed by MODIS and their backward trajectories further demonstrate that in pre-monsoon season, agricultural and forest fires in the northern India and Nepal were most likely sources of carbonaceous aerosol at QOMS. In addition to large-scale atmospheric circulation, the unique mountain/valley breeze system in the Himalayas can also have an important effect on air pollutant transport.

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Carbonaceous aerosols at urban influenced sites in Norway

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-19487-2008 ◽

2008 ◽

Vol 8 (6) ◽

pp. 19487-19525 ◽

Cited By ~ 1

Author(s):

K. E. Yttri ◽

C. Dye ◽

O.-A. Braathen ◽

D. Simpson ◽

E. Steinnes

Keyword(s):

Organic Carbon ◽

Carbonaceous Material ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Residential Areas ◽

Urban Background ◽

Wood Burning ◽

Pm10 And Pm2.5 ◽

The Impact ◽

Suburban Site

Abstract. Little is known regarding levels and source strength of carbonaceous aerosols in Scandinavia. In the present study, ambient aerosol (PM10 and PM2.5) concentrations of elemental carbon (EC), organic carbon (OC), water-insoluble organic carbon (WINSOC), and water-soluble organic carbon (WSOC) are reported for a curbside site, an urban background site, and a suburban site in Norway in order to investigate their spatial and seasonal variations. Aerosol filter samples were collected using tandem filter sampling to correct for the positive sampling artefact introduced by semi volatile OC. Analyses were performed using the thermal optical transmission (TOT) instrument from Sunset Lab Inc., which corrects for charring during analysis. Finally, we estimated the relative contribution of OC from wood burning based on the samples content of levoglucosan. Levels of EC varied by more than one order of magnitude between sites, likely due to the higher impact of vehicular traffic at the curbside and the urban background sites. In winter, the level of particulate organic carbon (OCp) at the suburban site was equal to (for PM10) or even higher (for PM2.5) than the levels observed at the curbside and the urban background sites. This finding was attributed to the impact of residential wood burning at the suburban site in winter, which was confirmed by a high mean concentration of levoglucosan (407 ng m−3). This finding indicates that exposure to primary combustion derived OCp could be equally high in residential areas as in a city center. It is demonstrated that OCp from wood burning (OCwood) accounted for almost all OCp at the suburban site in winter, allowing a new estimate of the ratio TCp/levoglucosan for both PM10 and PM2.5. Particulate carbonaceous material (PCM = Organic matter + Elemental matter) accounted for 46–83% of PM10 at the sites studied when considering the positive artefact of semi volatile OC, thus being the major contributor to PM.

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Carbonaceous aerosols on the south edge of the Tibetan Plateau: concentrations, seasonality and sources

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-1573-2015 ◽

2015 ◽

Vol 15 (3) ◽

pp. 1573-1584 ◽

Cited By ~ 123

Author(s):

Z. Cong ◽

S. Kang ◽

K. Kawamura ◽

B. Liu ◽

X. Wan ◽

...

Keyword(s):

Tibetan Plateau ◽

Organic Carbon ◽

Monsoon Season ◽

Air Pollutant ◽

Water Soluble ◽

Atmospheric Environment ◽

The Tibetan Plateau ◽

Carbonaceous Aerosols ◽

The South ◽

Aerosol Composition

Abstract. To quantitatively evaluate the effect of carbonaceous aerosols on the south edge of the Tibetan Plateau, aerosol samples were collected weekly from August 2009 to July 2010 at Qomolangma (Mt. Everest) Station for Atmospheric and Environmental Observation and Research (QOMS, 28.36° N, 86.95° E, 4276 m a.s.l.). The average concentrations of organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon were 1.43, 0.25 and 0.77 μg m−3, respectively. The concentration levels of OC and EC at QOMS are comparable to those at high-elevation sites on the southern slopes of the Himalayas (Langtang and Nepal Climate Observatory at Pyramid, or NCO-P), but 3 to 6 times lower than those at Manora Peak, India, and Godavari, Nepal. Sulfate was the most abundant anion species followed by nitrate, accounting for 25 and 12% of total ionic mass, respectively. Ca2+ was the most abundant cation species (annual average of 0.88 μg m−3). The dust loading, represented by Ca2+ concentration, was relatively constant throughout the year. OC, EC and other ionic species (NH4+, K+, NO3− and SO42−) exhibited a pronounced peak in the pre-monsoon period and a minimum in the monsoon season, being similar to the seasonal trends of aerosol composition reported previously from the southern slope of the Himalayas, such as Langtang and NCO-P. The strong correlation of OC and EC in QOMS aerosols with K+ and levoglucosan indicates that they mainly originated from biomass burning. The fire spots observed by MODIS and backward air-mass trajectories further demonstrate that in pre-monsoon season, agricultural and forest fires in northern India and Nepal were most likely sources of carbonaceous aerosol at QOMS. Moreover, the CALIOP observations confirmed that air-pollution plumes crossed the Himalayas during this period. The highly coherent variation of daily aerosol optical depth (500 nm) between QOMS and NCO-P indicates that both slopes of the Himalayas share a common atmospheric environment regime. In addition to large-scale atmospheric circulation, the unique mountain/valley breeze system can also have an important effect on air-pollutant transport.

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