CONTAMINATION RELATED TO ANTHROPIC ACTIVITIES. CHARACTERIZATION AND REMEDIATION

Organic and inorganic components of aerosols over the centralHimalayas: winter and summer variations in stable carbonand nitrogen isotopic composition

Prashant Hegde1,2 & Kimitaka Kawamura2 & H. Joshi3 & M. Naja3

Received: 21 April 2015 /Accepted: 4 October 2015# Springer-Verlag Berlin Heidelberg 2015

Abstract The aerosol samples were collected from a highelevation mountain site, Nainital, in India (1958 m asl) duringSeptember 2006 to June 2007 and were analyzed for water-soluble inorganic species, total carbon, nitrogen, and theirisotopic composition (δ13C and δ15N, respectively). Thechemical and isotopic composition of aerosols revealed sig-nificant anthropogenic influence over this remote free-troposphere site. The amount of total carbon and nitrogenand their isotopic composition suggest a considerable contri-bution of biomass burning to the aerosols during winter. Onthe other hand, fossil fuel combustion sources are found to bedominant during summer. The carbon aerosol in winter ischaracterized by greater isotope ratios (av. −24.0‰), mostlyoriginated from biomass burning of C4 plants. On the contrary,the aerosols in summer showed smaller δ13C values (−26.0‰), indicating that they are originated from vascular plants(mostly of C3 plants). The secondary ions (i.e., SO4

2−, NH4+,

and NO3−) were abundant due to the atmospheric reactions

during long-range transport in both seasons. The water-soluble organic and inorganic compositions revealed that theyare aged in winter but comparatively fresh in summer. Thisstudy validates that the pollutants generated from far distant

sources could reach high altitudes over the Himalayan regionunder favorable meteorological conditions.

Keywords Himalayan aerosols . Biomass burning . Fossilfuel combustion . Long-range transport . Pollution assessment

Introduction

Tropospheric aerosols have significant impacts on climatechange and human health, and their effects are largely dependenton their chemical composition (e.g., Krueger et al. 2003).Because of the potency and diversity of sources for both naturaland anthropogenic aerosols, there has been considerable intereston the characterization of emissions fromAsian region (Arimotoet al. 2004). Changes in emissions of soot, inorganic anions aswell as cations, sea salts, mineral dust, and a variety of industrialeffluents can all contribute to the variability in the chemicalcomposition of aerosols. Furthermore, due to the relatively shortlifetime of atmospheric particles, their concentrations and com-position vary widely on a regional scale.

The biogeochemical cycles of several chemical species in theatmosphere are perturbed by anthropogenic activities (Lacauxand Artaxo 2003). For example, Galloway (1995) reported thatNH3 emission and subsequent nitrogen accumulation in terres-trial ecosystems have the potential to generate significant acidi-fication in terrestrial and aquatic ecosystems. Fixed nitrogen(NO3

−, NH4+) is a limiting nutrient in many ecosystems. The

increased nitrogen deposition in and around many industrialareas of the world consequently causes eutrophication of freshwater and marine ecosystems, with consequence of affecting theatmospheric carbon balance (Brasseur et al. 2003). In fact,Novakov and Penner (1993) reported that organic carbon andsulfate aerosols equally contribute to the formation of cloudcondensation nuclei even in the remote marine regions.

Responsible editor: Philippe Garrigues

* Prashant Hegdehegdeprashant@yahoo.com

1 Space Physics Laboratory, Vikram Sarabhai Space Centre,Trivandrum, India

2 Institute of Low Temperature Science, Hokkaido University,Sapporo, Japan

3 Aryabhatta Research Institute of Observational Sciences,Nainital, India

Environ Sci Pollut ResDOI 10.1007/s11356-015-5530-3

Therefore, regional scale studies of chemical composition ofatmospheric particles are vital in assessing the effects of aerosolson climate. It is also important for better understanding variousatmospheric processes such as lateral and vertical air mass trans-port and physico-chemical transformations of atmosphericchemical species.

The research on stable isotope finds its applications in a widearea from compound specific to bulk analysis (Bendle et al.2006, 2007; Flanagan et al. 2005). In the atmospheric aerosols,isotope geochemistry will help in identifying the transport path-way of terrestrial biomarker compounds (Schefub et al. 2003;Yamamoto et al. 2013). Stable carbon isotopic compositions oftotal carbon (TC) (δ13C) and total nitrogen (TN) (δ15N) are alsouseful in source determination based on unique signals of differ-ent aerosol carbon and nitrogen. Further, it can also be used forinvestigating the long-range atmospheric transport of aerosols(Jung and Kawamura 2011 and references therein). The δ13Cvalue of the aerosol sample can yield important information onthe source of organic matter (Smith and Freeman 2006). It isshown that the δ13C value is in the range of −23 to −30‰ inC3 plants like shrubs, grasses, sedges, etc. (Gelencser 2004),while it is greater (−14 to −20‰) in C4 plants, for examplemaize, sugarcane, etc. (Saxena and Ramakrishnan 1984;Turekian et al. 1998).

The Indo-Gangetic Plain (IGP) is one of the most populatedregions in the world. The area includes some of the major Indianindustrialized cities such as Delhi, Kanpur, Lucknow, Patna, andKolkata. This region is rich in river alluvium and good for cul-tivation. Silt and clay make the fine particles whereas sand andgravel that are calcareous sediments make the land very fertile.Farming on the IGP primarily consists of sugarcane and wheatgrown in rotation during different seasons. Other crops includemaize, rice, and cotton. The highly irrigated productive land ofIndo-Gangetic plains contribute about 15 % of the world annualwheat production (Ortiz et al. 2008). Air masses originated fromthis anthropogenically influenced IGP region are enriched withcrop residue burning products and industrial emissions.Throughout the year, this pollution effect is seen all over theIndian subcontinent including oceanic regions, which becomesintense during winter months (Niranjan et al. 2006; Kumar et al.2011), and the influence may even extend to the Pacific duringthe latter part of the year.

The nature and sources of particulate matter at four Chineseurban locations were investigated using state-of-the-art offlineanalytical approaches and statistical techniques during January2013 (Huang et al. 2014). The authors found that the severe hazepollution event was driven to a large extent by secondary aerosolformation. The fossil fuel combustion and biomass burningwerefound to be important factors for controlling the level of pollut-ants in the atmosphere. In particular, the accumulation of highlyconcentrated fine particles in the boundary layer contributes tothe occurrence of Haze. The low temperature and relative hu-midity less than 90 % create the poor horizontal visibility. Fog

can occur if the wind is calm and the air is sufficiently moist,cool, and descending. Such conditions are prevalent in the Indo-Gangetic Plain during winter months of November to February(average temperature 17 °C, RH 64 %, and maximum dailyRH>90 %) as evidenced during an observational campaign(Mehta et al. 2009 and references therein). Tare et al. (2006)found that prolonged foggy/hazy conditions over the IGP regionare mainly due to the increased anthropogenic emissions overthe northern part of the Indian subcontinent. It is also shown thatseveral secondary pollutants such as ammonium, nitrate, andsulfate are high especially among fine particles in the haze pol-lution (Wang et al. 2012).

There are different approaches for identifying the source re-gions of pollution using back-air trajectory, 3-D modeling basedon the tracer, and observations of different chemical species.Studies on physical and chemical properties of background aero-sols can also help to identify the source regions. High altitudepristinemountain sites can provide a unique opportunity to studythis aspect. As compared to the lowland areas (e.g., metropolitancities), the stronger solar radiation, higher relative humidity, andlower temperature over the mountain region provides a uniquesite for the study of aerosols. Present observation site ManoraPeak, Nainital (29.4°N; 79.5°E, 1952 m asl) (hereafter referredto as Nainital) is one of the highest mountain peaks in the foot-hills of the central Himalayan region (Fig. 1). As the summit ofthe world, the Himalayan chain of mountains acts as the bound-ary of the Indian monsoon and the continental climate of centralAsia. South Asian climate is greatly influenced by theHimalayan chain. The high elevation acts as a barrier over theIndian subcontinent for the entry of cold air mass from centralAsia and retains the moist air flow originated over the IndianOcean (Barros et al. 2004). Due to its geographical location andhigh altitude, the site Nainital can be considered as a uniqueplace to understand the atmospheric chemistry and processesamong remote sites across the world.

The objective of this work is to better understand the sourcesand chemical characteristics of aerosols over the Himalayan re-gion. We present the temporal variations of water-soluble ions(cations and anions), stable isotope ratios of total carbon andnitrogen, organic carbon, elemental carbon and water-solubleorganic carbon, and their sources for different seasons of theyear (winter and summer). Since the present observation site isat a mountain of high altitude and has minimal local emissions,we believe that the study of aerosols at Nainital represents, to theextent possible, a regional scenario over the subcontinent.

Experimental details

Aerosol sampling

Total suspended aerosol particles in the atmosphere were col-lected from a single-stage high-volume sampler using a quartz

Environ Sci Pollut Res

fiber filter (precombusted at 450 °C for 6 h) on the rooftop(∼10 m agl) of a building at Nainital (Fig. 1). Aerosol sampleswere collected from September 2006 to January 2007(representing winter season) and March to June 2007(representing summer season). The sampling was done fordaytime (9 am to 6 pm) and nighttime (7 pm to 8 am) duringwinter, whereas during summer period the sampler was oper-ated for less duration: daytime (10 am to 1 pm) and nighttime(8 pm to 11 pm). Field blank filters were also collected in thesameway except for a zero flow rate. In total, nine filed blankswere collected representing a minimum of 1 for each month.Before and after sampling, the filters were stored in aprecleaned glass bottle with a Teflon-lined screw cap at−20 °C.

Chemical analysis

All the samples were sent to the Institute of Low TemperatureScience, Hokkaido University, Sapporo, for the analysis.

Total carbon, total nitrogen, and their isotope analysis

TC and TN and their isotope ratios (δ13C and δ15N) weremeasured using an elemental analyzer (EA) (Carlo Erba, NA1500) and an isotope ratio mass spectrometer (irMS)(Finnigan MAT Delta Plus) coupled to the EA through aninterface (Thermo Quest, ConFlo II), respectively(Kawamura et al. 2004). A part of the filter paper (a disc of

1.8 cm in diameter) was placed in a tin cup, which was intro-duced into EA and oxidized at 1020 °C in a combustion col-umn that is packed with chromium(III) oxide. The emittednitrogen oxides were converted to molecular nitrogen (N2) at650 °C in a reduction column, which is packed with metalliccopper. By using a gas chromatograph (GC) in line with theEA, the derived N2 and carbon dioxide (CO2) were separatedand measured from a thermal conductivity detector. The CO2

and N2 were then introduced into the irMS. From the standardisotopic conversion equation, the carbon isotopic composition(δ13C) relative to the Pee Dee Belemnite (PDB) standard wasestimated as follows.

δ13C ¼13C

.12C

� �sample

� �

13C.

12C� �

standard

� �h i −1

2664

3775� 1000

Known amounts of acetanilide were used as external stan-dard to calculate mass concentrations of TC, TN, and δ13C ofTC (δ13CTC) as well as δ15N of TN. Different amounts ofstandards (0.2 to 0.6 mg of acetanilide, whose δ13C is−27.26‰) were prepared and measured by the EA-irMS.Field blank corrections were also made for the mass concen-trations and δ13CTC values reported here by applying isotopemass balance equations (Turekian et al. 2003). For the qualityassurance, field blank filters were treated as the real samples.TC and TN blank levels were 1.5 and 1.0 % of the measuredconcentrations, respectively. The triplicate analyses of the

(4)

(3)

(2)

(1)

Nainital

Fig. 1 Mass plot of air mass back-trajectories arriving at 500 m above Nainital during the observation period, showing four broad pathways.Geographical location of Nainital over the Indian subcontinent is given (Map provided by http://earth.google.com)

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filter sample reveal that analytical errors in the TC and TNmeasurements were 2.0 and 4.0 %, respectively.

Determination of water-soluble inorganic species

Water-soluble inorganic species were measured using ionchromatography (IC, Metrohm 761). A part of the quartz filter(1.8 cm disc) was extracted with 10 ml of Milli-Q water in anultrasonic bath for 30min. The extracts were filtered through asyringe filter (Millipore, Millex-GV, 0.45 μm) and theninjected to the IC. Metrosep C2 column (150 mm) was usedfor the measurement of sodium (Na+), ammonium (NH4

+),potassium (K+), and calcium (Ca2+) ions with eluent 4 mMtartaric acid/1 mM 2,6-pyridinedicarboxylic acid. Shodex SI-90 4E column was used for the determination of nitrate(NO3

−), sulfate (SO42−), methanesulfonate (MSA−,

CH3SO3−), and chloride (Cl−), using 1.8 mM Na2CO3/

1.7 mM NaHCO3 as eluent. Field blanks were used to definethe minimum detection limits of NO3

−, SO42−, and NH4

+,which are 0.01, 0.11, and 0.03 μgm−3, respectively.Magnesium (Mg2+) ion concentrations in the samples werefound to be less than the detection limit. It must be mentionedhere that the analytical errors were below 1.3 % based on thetriplicate analyses of the filter sample (Aggarwal 2010;Aggarwal et al. 2013).

WSOC, OC, and EC

For the measurement of water-soluble organic carbon(WSOC), an aliquot of the filter was extracted with organic-free Milli-Q water using an ultrasonic bath. Particles in thewater extracts were removed by filtration with a membranedisc filter (Millex-GV, Millipore, 0.22 μm) and injected to atotal organic carbon (TOC) analyzer (Shimadzu, TOC-VCSH)(Aggarwal and Kawamura 2008). The minimum detectionlimit for the entire set of measurement was 0.1 μg cm−3 witha maximum of 15 % analytical errors. An OC/EC analyzerfrom Sunset Laboratory Inc., Portland, USA was employedfor the measurement of organic carbon (OC) and elementalcarbon (EC). The detection limits of these measurements were1 μg m−3 for OC and 0.2 μg m−3 for EC. Concentrations of allthe species reported here are corrected for field blanks.

Meteorology

In situ measurements of the meteorological parameters weremade at the sampling site during the study period by usingautomatic weather station (Campbell Scientific Inc., Canadaand Dynalab, India) with a time resolution of 20 min. Thevariation of daily average temperature (T), relative humidity(RH), wind speed (WS), wind direction (WD), and daily totalrainfall for September 2006 to June 2007 at Nainital areshown in Fig. 2. It is clear that the lowest temperature was

recorded during December and January with the values belowzero. The highest temperature was observed (around 18 to19 °C) during May and June with the maximum temperaturesreaching up to 25 °C. Relative humidity shows a gradual de-crease by the withdrawal of monsoon rains. Lowest RH wasrecorded during December and January. Wind speed remainslow during December to March (∼2 m s−1); however, higherwind speeds were noticed during April andMay. Surface winddirection does not show significant seasonal variations. Inaddition, northerly or northeasterly winds are observed duringvery few occasions, mainly due to the topography of thisregion. The annual total rainfall averages around 250–300 cm and occurs mostly during southwest monsoon. Theobservation site represents free-troposphere characteristicsmainly during winter.

Air mass trajectories

Seven-day back-air trajectories were computed using theHybrid Single Particle Lagrangian Integrated Trajectory(HYSPLIT) model of the National Oceanic andAtmospheric Administration (NOAA) during the sam-pling period. Figure 1 shows the isentropic air mass backtrajectory for the arrival height of 500 m above groundlevel at the observation site. Typically, atmospheric aero-sols may have residence time of 1 week to 10 days(Reddy and Venkataraman 1999). In view of this, 7-dayback-air trajectories were made here. Generally, trajectoryprovides the most likely pathway and source region for airmass. Nevertheless, accuracy of these trajectories is main-ly determined by the spatial and temporal resolutions ofmeteorological data used (e.g., Stohl and Koffi 1998; Najaet al. 2003). Figure 1 clearly shows four broad pathwaysof air masses reaching to the central Himalayas from (1)the southeast or IGP region, (2) the west (west Asianregions), (3) northwestern regions of Indian subcontinent,and (4) Thar desert regions and the Arabian Sea in thesouthwest.

It is important to note that the air masses do not arrive overthe sampling site from the northeastern sector, mainly due tothe presence of high mountains. By the withdrawal of mon-soon, the wind pattern during September is southwesterly andair masses circulate mostly over the Northern Indian region(yellow color lines in Fig. 1). The wind patterns graduallychange to westerly during January (purple color lines), whilein April and May they remain northerly (black color lines).The trajectory patterns change again from southwesterly towesterly during mid June (red color lines). More detail onthe general meteorology prevailing during different seasons,air mass, and topography around the observation site can beseen elsewhere (Sagar et al. 2004; Pant et al. 2006; Sarangiet al. 2014).

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Results and discussion

Water-soluble inorganic components

Linear regression plots between sum of cation equivalents(Na+, NH4

+, K+, and Ca2+) and anion equivalents (MSA−,Cl−, NO3

−, PO4−, and SO4

2−) for daytime and nighttime sam-ples are shown in Fig. 3. It is clear that there exists a highdegree of correlation (R2≥0.89) among the samples. Averageequivalent ratios of total anions to cations were 0.84±0.12(range, 0.66 to 1.10) in winter and 0.72±0.20 (0.41 to 1.05)in summer. Excess cations were observed especially duringsummer. The departure of data from 1:1 line could possiblyarise due to the contribution of HCO3

− and organic ions

during summer months. On the contrary, our previous studieshave shown that the water-soluble organic aerosols (especiallyoxalic acid) decrease during summer season (Hegde andKawamura 2012).

The summary on the analysis of TC, TN, and their isotoperatios and concentrations of inorganic ions is shown inTable 1. On average, SO4

2−, Na+, and PO4− concentrations

during winter were found to be two to three times higher thanthose in summer. Except for Ca2+, the concentrations of allother inorganic ions in nighttime were lower than those indaytime for both seasons. Inorganic ions are mostlytransported from lowland sources, thus more ions can betransported onto the mountaintop during daytime due tochanges in the boundary layer heights. During night, the tem-perature over the region remains very low and therefore thenocturnal stable boundary layer remains well below the obser-vation site. Since the local emissions are not much (due toremote site), most of the observed concentrations are lowestduring night. However, during daytime the ambient tempera-ture increases with increase in solar radiation and thermalsstart developing. The convective motions resulting from sur-face heating is relatively high over the surrounding valleyregion. Thereby, the ground-based capping inversion breaksand the pollutants from the low land areas are flushed out tohigher levels; hence, higher concentrations are noticed formost of the compounds over the observational site. Back-airtrajectories in Fig. 1 also clearly show the transport pathwayfor the air mass by the southwesterly and the westerly, whichcorresponds to high concentration of the species.

Since the maritime influence is insignificant over Nainital,Na+ might have a contribution from soil dust (Sun et al. 2010),which can heterogeneously react with acidic gases (e.g., SO2,

Fig. 2 The temporal variations ofambient meteorologicalparameters a daily averagetemperature, b relative humidity,c wind speed, d wind direction,and e daily total rainfall forSeptember 2006 to June 2007

Fig. 3 Linear regression plots between sum of anion equivalents (neq)and cation equivalents (neq) showing the charge balance in Nainitalaerosol samples

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NOx) and form water-soluble Na+ (Li et al. 2011). High cor-relations (R2≥0.9) were observed between Na+ and Ca2+ ex-cept for nighttime samples collected in winter (R2≥0.3). Theobserved concentrations of most inorganic ions in the presentsite are lower than those from lowland urban cities like NewDelhi, Kanpur, and Hisar in the IGP region (Tare et al. 2006).This is mainly attributed to the dilution effect as well as loss bydry/wet removal of aerosol particles during long-range trans-port. On the other hand, the secondary ions (i.e., NH4

+, NO3−,

and SO42) are abundantly produced by chemical processes

over high-altitude regions due to the sufficient time for thereactions during atmospheric transport. Previous studies overseveral high-altitude locations (e.g., Mt. Hua, Central China,2160 m asl; Li et al. 2011 and references therein) have indi-cated relatively higher abundance of secondary ions, whichare mainly attributed to transport from low land areas.

The order of abundances of major inorganic ions showsvery different trend for both the seasons except for SO4

2−

and Ca2+. SO42 shows maximum concentration during winter

followed by Ca2+>Na+>NH4+>K+>PO4

−>Cl−>NO3−>

MSA−. Similarly, during summer, SO42− was also found to

be maximum followed by Ca2+>NH4+>NO3

−>Cl−>K+>MSA−>Na+>PO4

−. The concentration of SO42− was two to

four times higher (5.3±2.2 and 4.4±1.8 μg m−3 for day andnight, respectively) in winter than in summer (2.7±1.6 and 1.1±6.5 μg m−3 for day and night, respectively). This high abun-dance of SO4

2− in aerosol samples during winter indicates thecontributions of biofuel and crop residue burning over the

region. The difference in seasonal contribution is possibledue to the type of fuel used over the source region (IGP).

Modeling studies in the past have estimated that fuel wood,dung cake, and crop waste are the three major sources of SO2

emissions over the Indian subcontinent, contributing 15, 55,and 5 Gg y−1, respectively (Habib et al. 2004; Venkataramanet al. 2006). Over the IGP region, dung cake is the commontype of biofuel used for house heating and cooking purposesespecially in winter. Some other in situ measurements over theIGP region indicate two to five times higher SO2 emissionsdue to the increased usage of biomass as domestic fuel duringwinter (Goyal and Sidhartha 2002; Gupta et al. 2003; Sharmaet al. 2010). In the mega city Chennai (13.04° N; 80.17° E)located on the southeast coast of India, Pavuluri et al. (2011)have observed twofold to threefold higher concentrations ofparticulate SO4

2− during winter than summer because ofhigher consumption of biomass/biofuels.

The major sources of both SO42− and NO3

− in the atmo-sphere are the oxidation of their gaseous precursors SO2 andNOx, respectively. Garg et al. (2001) reported that the aver-aged emission ratio of SO2/NOx from all pollutant sourcesover India is around 1.34. Rastogi and Sarin (2005) reportedlarge variations in SO4

2−/NO3− ratios of 2.0 to 19.4 for the

high-altitude location of Mount Abu. Higher SO42−/NO3

− ra-tio (37.7) was observed for winter season over Nainital.However, the SO4

2−/NO3− ratio during summer over the study

area (3.7) is very much comparable to those from other areasin the world (Rastogi and Sarin 2005 and references therein).

Table 1 Concentrations of total carbon (TC), total nitrogen (TN), and their isotope ratios and concentrations of inorganic ions over Nainital, India

Winter Summer

Day (N=9) Night (N=9) Day (N=11) Night (N=10)

Compounds Range Ave.±SD Range Ave.±SD Range Ave.±SD Range Ave.±SD

TC (μg c m−3) 5.3–11 7.9±2.18 4.8–9.8 6.9±1.7 9.1–36 21±9.5 11–30 17±6.2

TN (μg nm−3) 0.35–1.3 0.77±0.34 0.35–1.2 0.59±0.26 0.7–3.7 1.7±0.79 0.96–3.05 1.55±0.61

δ13C (‰) −25 to −23 −24±0.89 −25 to −23 −24±0.74 −27 to −24 −26±1 −27 to −24 −26±1.1δ15N (‰) 22–26 24±1.6 22–27 25±1.5 13–24 17±3.7 14–20 16±2

MSA− (μg m−3) 0.08–0.2 0.12±0.04 0.08–0.14 0.11±0.02 0.22–0.62 0.4±0.12 0.23–0.49 0.38±0.08

Cl− (μg m−3) 0.03–1.2 0.21±0.38 0.05–0.2 0.11±0.05 0.2–1.5 0.7±0.47 0.32–1.09 0.67±0.24

NO3− (μg m−3) 0.09–0.21 0.14±0.04 0.1–0.38 0.15±0.09 0.24–1.6 0.74±0.33 0.4–1.24 0.65±0.25

PO4− (μg m−3) 0.01–0.61 0.32±0.23 0.08–0.41 0.31±0.1 0.01–0.17 0.09±0.07 0.05–0.14 0.08±0.03

SO42− (μg m−3) 2.5–9.0 5.3±2.2 2.2–8.1 4.4±1.8 0.54–6.2 2.7±1.6 1.1–6.5 2.7±1.6

Na+ (μg m−3) 0.63–1.4 0.87±0.24 0.6–1 0.82±0.12 0.06–0.97 0.34±0.31 0.08–0.47 0.22±0.14

NH4+ (μg m−3) 0.08–1.1 0.57±0.36 0.1–0.94 0.36±0.26 0.28–2.1 0.84±0.47 0.45–1.76 0.75±0.4

K+ (μg m−3) 0.22–0.71 0.52±0.18 0.18–0.7 0.36±0.17 0.21–0.95 0.57±0.25 0.27–1.15 0.47±0.26

Ca2+ (μg m−3) 0.6–2.32 1.17±0.5 0.64–2.3 1.3±0.59 0.27–3.9 1.7±1.4 0.3–4.1 1.9±1.4

Inorg-N (μg m−3) 0.04–1.4 0.5±0.4 0.04–0.8 0.5±0.3 0.07–0.4 0.2±0.1 0.07–0.4 0.2±0.1

Org-N (μg m−3) 0.15–1.21 0.3±0.39 0.09–0.41 0.16±0.17 0.63–3.30 1.5±0.7 0.85–2.7 1.4±0.5

We also measured Mg2+ , but its levels were below detection limit.

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The air mass trajectories start mostly from the IGP regionduring winter, delivering the pollutants to the sampling site(Fig. 1). The observed higher ratios could also be due to thedifferences in regional pollution sources and more importantlydue to the altitude difference between the sites. NO3

− existslargely in coarser particles whereas SO4

2− follows a bimodal(fine and coarse mode) distribution of aerosols (Venkataramanet al. 2002; Tang et al. 2004; Ooki and Uematsu 2005).Updraft winds can transport finer particles to higher altitudeand bring relatively higher concentrations of SO4

2− than thatof NO3

− over Nainital, thereby making SO42−/NO3

− ratioshigh.

The sampling location in Nainital is considerably far fromthe oceanic source (>1000 km from both the Bay of Bengaland the Arabian Sea). Therefore, it is highly possible thatMSA−, Na+, and Cl− might have come from anthropogenicand/or natural sources. The Na+ concentrations were severaltimes higher during winter than summer; however, a contrarywas observed with MSA− and Cl− concentrations (Table 1).During summer, the MSA concentrations were several timeshigher (0.39±0.1 μg m−3) than those during winter (0.11±0.03 μg m−3). The largest supply of gaseous sulfur to theatmosphere is marine water. Natural MSA is produced bythe oxidation of dimethyl sulfide (DMS) produced in the sur-face ocean by phytoplankton species. It is an important bio-genic precursor gas for MSA and sulfate (SO4

2−) in aerosolsthat alter the Earth’s radiative forcing directly by scatteringsolar energy and indirectly by acting as cloud condensationnuclei (CCN). MSA values over Nainital (annual average;0.25 μg m−3) are several times higher than those(∼100 ng m−3) reported from marine aerosols (e.g., Ayersand Gras 1991) and those (9 to 95 ng m−3) from the high-latitude forest region (Sapporo, Japan; Miyazaki et al. 2012).Lamb et al. (1987) reported that the observed higher MSAconcentrations were due to either enhanced contributions frommaritime sources or oxidation of terrestrial biogenic DMS.Andreae et al. (1990) reported emissions of sulfur gases (in-cluding DMS) from deciduous trees and pines. From the back-ground air pollution monitoring site in Hungary, which is farfrom anthropogenic sources, lower concentrations of MSA(10 ngS m−3) were reported in coarse mode aerosol particles(Lukács et al. 2009).

High correlations were observed between MSA and OCespecially in the summer period (R≥0.78) at Nainital, indicat-ing its origin from biogenic/biomass burning sources.Meinardi et al. (2003) have identified MSA during both theflaming and smoldering stages of the savannah bush fire inAustralia’s Northern Territory, which contributes ∼10% of theatmospheric sulfur emitted by biomass burning. Laboratoryexperiments suggest that DMS in the atmosphere reacts withhydroxyl radical during daytime, thereby producing substan-tial amounts of MSA and SO2 (Grosjean 1984). Similarly,some other experiments (e.g., Kolaltis et al. 1989) also

indicated that MSA oxidizes further to yield SO42−.

Conversely, in the samples over Nainital, any clear linear re-lation was not found between MSA and SO4

2−.Calcium was the second dominant inorganic ion for both

seasons. Soil and crustal material significantly contributes tonatural Ca2+ and therefore it is widely used as a tracer elementfor windblown dusts from deserts and arid regions (Lee et al.2003; Yadav and Rajamani 2004). Apart from the aeoliansources, Ca2+ may also come from urban construction activi-ties (e.g., cement industries). Minor forms of calcium such asCa3 (PO4)2 may not contribute to the measured Ca2+ becauseof their limited solubility. In our samples, Ca2+ shows highpositive correlations with anthropogenic tracers like NH4

+,K+, and SO4

2− for both winter and summer (R2≥0.75). Overthe greater Himalaya region (e.g.,Mount Everest; 6520m asl),the aerosol measurements conducted by Cong et al. (2010)revealed that the major contribution was of aluminum silicatesand calcium carbonate (>71 %). Calcite is the most abundantmineral found over the northwestern arid regions surroundedby the Arabian Sea. These calcite crystals will get lifted withdust particles and undergo reactionwith atmospheric sulfate toproduce calcium sulfate (i.e., gypsum) (Takahashi et al. 2008).Mori et al. (1998) found that ammonium sulfate reacted withcalcium carbonate in Kosa (Asian dust) particles. It is alsolikely that Ca2+ may be present in mixed state with anthropo-genic aerosols over Nainital.

K+ is generally considered as a good tracer for biomassburning (including biofuel) (Lee et al. 2003 and referencestherein; Falkovich et al. 2005). In our samples, K+ did notshow clear seasonal variations but showed a good correlationwith NH4

+ and SO42− (R2≥0.75) for both winter and summer.

High correlations (R2=0.86) were observed during summerseason for both K+ with NO3

−, implying that biofuel is animportant source of this aerosol component.

Aerosol NH4+ may be derived from biomass burning as

well as livestock and agricultural activities (Olivier et al.1998). In our samples, NH4

+ shows high correlation withNO3

− for summer season (R2=0.98 and 0.99 for day andnight, respectively) but lower correlation during winter (R2=0.78 and 0.69 for day and night, respectively). These contem-poraneous variations suggest that NH3 shared common emis-sion sources with NO3

− and SO42− and their precursors (Lee

et al. 2003).Over the study region, relatively high concentrations of

PO43− were observed during the winter period (ranging from

0.01 to 0.61 μg m−3 with an average of 0.32±0.15 μg m−3).Lesser amounts of PO4

3− were recorded during the summerperiod (∼0.09 μg m−3). Nevertheless, daytime and nighttimevariations of the concentration did not show much difference.Previous studies from USA and Asia including some of theurban sites over Bangladesh have reported PO4

3− concentra-tions of 0.08 to 0.16 μg m−3 (Salam et al. 2003). These report-ed values are very much comparable to the observations over

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Nainital. However, higher concentrations of PO43− (3.1±

1.6 μg m−3) were reported over Ulaanbaatar, Mongolia byJung et al. (2010), the source of which has been attributedfrom extensive use of fertilizers as well as phosphate-containing minerals that exist in the local soil. Nonetheless,no clear correlations were noticed for PO4

3− either with ter-restrial or anthropogenic tracers at Nainital.

TC content and stable carbon isotope ratios

Figure 4 shows the temporal variation of TC and its isotopiccomposition along with K+ and SO4

2−. During summer, theTC concentration was found to be ∼3 times higher (21±9.5and 17±6.2 μg m−3 for day and night, respectively) than thosein winter (7.9±2.18 and 6.9±1.7 μg m−3, respectively).However, nighttime concentrations of TC were considerablylower (by ∼20 %) than daytime averages for both seasons(Table 1). Minor variation in TC concentrations during winterindicates a consistent source of carbonaceous material.Interestingly, for nighttime samples from both seasons, TCshows good correlation with SO4

2− (R2=0.72). The annualaverage TC concentration over Nainital (14±8.5 μg m−3) iscomparable to that of many Indian cities (Satheesh 2012) butsignificantly higher than those from the European urban back-ground sites (Fisseha et al. 2009 and references there in).

Figure 4 (bottom panel) shows the time variations of δ13Cvalues of Nainital aerosols. Summer δ13C values are slightlysmaller (−26±1.1‰) than the winter values (−24±0.89‰).The differences in average δ13C values for winter versus sum-mer might indicate that the major sources for TC from thesource region (IGP) change with season. Figure 5 comparesthe δ13C values measured in our Nainital aerosol samples withthose reported for various locations as well as prospectivesources. Generally, C3 plants burn with emitting aerosol with

an average δ13C value of −26.5‰ and a maximum fraction-ation of −0.5‰. However, C4 plants are characterized by agreater δ13C ratio of −17.0‰ with isotopic fractionation of3.5‰ (Cachier et al. 1986; Turekian et al. 1998). On thecontrary, Huang et al. (2006) found that biomass burning fromthe forests may have higher isotopic fractionation of>3.5‰,as compared to vehicle emissions studied from road tunnels(≈0; homogeneous high temperature processes). C4 plantswhich include sugar cane, corn, bamboo, grasses, desertplants, and salt marsh plants are very common and are oftenburnt over northwestern India during winter season. Peat andlignite classes of coal that have a δ13C value close to −23.8‰(Mikolajczuk et al. 2008) are also extensively used for househeating, domestic cooking, and energy production over theIGP region during the winter period. Stein and Rudolph(2007) estimated the δ13C value of −26.0‰ for ethane emis-sions from fossil fuel and industrial biofuel combustion.

Stable carbon isotopic composition (δ13C) observed in thepresent study has been compared with those in the reportedliterature (Fig. 5). As compared to the aerosols over Nainital,Agnihotri et al. (2011) reported relatively smaller δ13C valuesover the Bay of Bengal (−26.5‰) and the Arabian Sea region(−25.6‰), which may be attributed to carbonaceous aerosolsof continental/anthropogenic origin. Pavuluri et al. (2011)measured δ13C ratios from the tropical Indian aerosols(PM10) collected on daytime and nighttime basis in winterand summer, 2007 from Chennai and inferred that biofuel/biomass burning is the major source of aerosol carbon inSouth and Southeast Asia. Urban locations such as Mumbai(Aggarwal et al. 2013) and Mexico cities (López-Veneroni2009) reported δ13C values of −26.2±0.3 and −25.1‰, re-spectively, mainly due to the fossil fuel combustion, and arecomparable to summer average values over Nainital. On thecontrary, δ13C of aerosols over Nainital are much lower

Fig. 4 Temporal variation of TCand its isotopic ratios (δ13C)along with water-soluble K+ andSO4

2− in aerosol samplescollected at Nainital, India

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(−20.9±0.8‰) than those reported from Piracicaba, Brazil,where the C4 plant burning was expected (Martinelli et al.2002).

Water soluble and insoluble carbonaceous components

Understanding the composition of WSOC in smoke aerosolsis particularly important for tropical regions (Mayol-Braceroet al. 2002). In general, aerosols originated from biomassburning are more water-soluble than are fossil fuel combus-tion products (which are mostly water-insoluble). From thesample collected over Nainital, concentrations of water-insoluble organic carbon (WIOC) are calculated bysubtractingWSOC fromOC. A triangular diagram is depictedin Fig. 6 for WSOC, WIOC, and EC. It is quite clear thatWSOC contribution is significantly higher during winter sea-son, whereas during summer WIOC and EC dominate thebulk aerosol composition.

In the past, Huang et al. (2006) observed that organic car-bon is released at relatively low temperature (550 °C), where-as elemental carbon or black carbon may be emitted by high

temperature combustion (>800 °C). The temporal variationsof EC, OC, and WSOC along with TC/SO4 and MSA areshown in Fig. 7. The average OC concentrations in summerwere about three times higher than that during winter(Table 1). A similar trend was observed with concentrationsof TC, but a contrary is observed with WSOC. This clearlyindicates that biomass burning or biogenic (both primary andsecondary) emissions dominate during winter whereas aero-sols during the summer are influenced by anthropogenic in-puts. The average K/EC and K/OC ratios in winter (0.36 and0.18, respectively) were several times higher than those insummer (0.07 and 0.04, respectively), indicating that fossilfuel combustion significantly contributes in the latter season.Lower K/EC ratio (0.03) was reported by Wang et al. (2005)from Auckland, New Zealand, where vehicular emissionsdominate.

In order to identify sources as well as emission and trans-formation features of carbonaceous aerosols, the mass ratiosof OC to EC or BC have been extensively used in the previousstudies (e.g., Turpin and Huntzicker 1991; Clarke et al. 2002).However, it is important to note that the differences in analyt-ical approaches could significantly influence the results usingthese ratios. BC concentrations (Aethalometer measurements)from a network of eight observatories spread over geograph-ically distinct environments of India are examined duringMarch–May 2006, for their spatio-temporal characteristics(Beegum et al. 2009). During this period, BC concentrationsshowed large variations across the country with values rang-ing from 0.065 μg m−3 over the Arabian Sea to 27 μg m−3

over the industrial/urban areas. Over the Eastern Atlantic,Malm et al. (1994) reported that the low ratio of BC/TC(∼0.15) for the PM2.5 aerosol can be attributed to a significant

Fig. 5 Stable carbon isotopic compositions (δ13C) of potential sources ofcarbon in Nainital aerosols. Data with range or mean (including standarddeviation) were taken from the following sources: a this study; bAgnihotri et al. 2011; c Pavuluri et al. 2011; d Cachier et al. 1985; eNarukawa et al. 1999; f Martinelli et al. 2002; g Huang et al. 2006; hLópez-Veneroni 2009; i Aggarwal et al. 2013; j Turekian et al. 1998, andk Widory et al. 2004

Fig. 6 Compositions of elemental carbon (EC), water-soluble organiccarbon (WSOC), and water-insoluble organic carbon (WIOC) (given aspercentage fractions of TC) in aerosol samples collected at Nainital, India

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contribution of organic material that may be of biogenic orsecondary anthropogenic origin. From the results obtainedduring three INDOEX research flights, Novakov et al.(2000) have estimated the contribution (in mass) of fossil fuelcombustion to the carbonaceous aerosol to be∼80 % usingmeasured BC/TC ratios. During the 2004 to 2007 period,BC observations over Nainital reveal average concentrationsof 0.99±0.02 μg m−3 (Dumka et al. 2010), which is attributedto fossil fuel combustion.

Novakov and Corrigan (1996) showed that water-solubleorganic species in smoke particles produced from smolderingcombustion process have a close link to CCN activity. Further,through field experiments, Roberts et al. (2002) establishedthat hydrophilic organic matter can become active in associa-tion with the water-soluble inorganic species. Aerosol OCmay contain a significant quantity of other elements such asO, N, and H; therefore, particulate organic matter (POM) isestimated. From the theoretical and laboratory studies, a mul-tiplication factor of 1.2 to 2.6 is used in published literatures toestimate the aerosol total organic mass depending on the urbanor non-urban sampling location (Turpin and Lim 2001). Wehave used a factor of 1.6 for POM estimation in the presentstudy. The factor chosen here is a function of composition ofthe aerosol sampled, its origin, and its degree of aging(Puxbaum and Tenze-Kunit 2003).

Figure 8 presents pie diagrams for relative contributions ofwater-soluble organic matter (WSOM) and water-insolubleorganic matter (WIOM), along with other major inorganicions in both winter and summer. During summer, WIOM con-tribution (37 %) is found to be higher than that during winter(19 %). In fact, Venkataraman et al. (2002) have suggestedthat a higher ratio of organic matter (OM) to SO4

2− indicates astronger biomass burning influence and less photochemicalaging. Smaller values are indicative of stronger anthropogenicinfluences and more photochemical aging. In Nainital, OM/SO4

2− ratio was several times higher in summer (11.4) than inwinter (2.21). Ziemba et al. (2007) reported larger OM/SO4

2−

ratio (6.4) for a rural site (Durham, New Hampshire), whichhas been attributed to a strong biogenic emission and lessphotochemical aging. However, the same study revealed rel-atively small OM/SO4

2− ratio (0.4) for the aerosols that areattributed to enhanced anthropogenic influence and photo-chemical aging.

Primary emissions from biomass burning (includingcooking) as well as secondary organic aerosols are consideredto be the major sources of WSOC in atmospheric aerosols(Chebbi and Carlier 1996). Ho et al. (2006) used WSOC/ECratios as an indicator for aged aerosol (e.g., due to photochem-ical reactions). The averageWSOC/EC value is higher in win-ter (2.5±0.8) than in summer (1.6±1.3), indicating an

Fig. 7 The temporal variations ofEC, OC, and WSOC along withMSA and TC/SO4 in aerosolsamples collected at Nainital,India

Environ Sci Pollut Res

enhanced contribution of fresh aerosols during summer. Theannual average of WSOC/EC values (2.0±1.2) is found to beconsiderably higher than the previous measurements conduct-ed for a high traffic roadside site in Paris (0.32) (Ruellan andCachier 2000), but similar to Hong Kong (2.1) (Ho et al.2006). There may also be other important sources of WSOCin the study area, such as soil resuspension, fuel combustion(Urban et al. 2012), and formation of secondary water-solubleorganic aerosol via gas phase photochemical reactions (Hagleret al. 2007; Lim et al. 2010). Previous studies have shown thatWSOC/OC ratios increased with the photochemical aging ofaerosols (e.g., Agarwal et al. 2010). The increase in WSOC/OC ratios has been interpreted by a photochemical transfor-mation of primary organic aerosols to WSOC and/or a forma-tion of water-soluble secondary organic aerosol (SOA) viagas-to-particle conversion during long-range atmospherictransport (Aggarwal and Kawamura 2009). In Nainital aero-sols, relatively high WSOC/OC ratios were observed duringwinter season (0.51±0.06) compared with those in summerseason (0.33±0.13), indicating the photochemical aging ofaerosols in the earlier season.

TN content and nitrogen isotope ratios

Seasonal variation in the concentrations of TN and its isotopiccomposition (δ15N), along with water-soluble NH4

+ and NO3−

in aerosol samples collected at Nainital, are depicted in Fig. 9.TN concentrations during winter were on average 0.77±0.34and 0.59±0.26 μg m−3 for day and night, respectively. Duringsummer, the concentration of TN was almost doubled (1.71±0.79 and 1.55±0.61 μg m−3 for day and night, respectively).The variations of daytime and nighttime concentrations werenot statistically significant. However, on 3 January 2007, thenighttime concentrations were three times lower than those ofthe daytime sample on the same day, whereas the reverse wasobserved on 30 May 2007. The higher TN content in aerosolsover Nainital during summer is probably related to greaterNOx species present in aerosols from fossil fuel burning(Pichlmayer et al. 1998). According to Galloway (2000), ni-trogen compounds transported from the Asian continent ismainly from fossil fuel burning and fertilizer use in agriculturesector.

Previous studies have reported that Asian aerosols contain∼40 % of nitrogen in the form of water-soluble nitrate(Kawamura et al. 2004 and references therein). In our sam-ples, also 35±16 % was found to be inorganic nitrate in TN.Interestingly, samples collected during summer showed a con-siderably higher contribution of NO3

− to TN (43±8 %) thanthat during winter (26±18%). On the other hand, as comparedto winter, the NH4

+ contribution to TN reduced to half duringsummer season. Further, for the entire study period, very goodcorrelations (R2≥0.88) were observed between NO3

− plusNH4

+ with TN (Fig. 10). From these results, it is apparent thatnitrate and ammonium ions account for a significant portion ofTN. The aerosols enriched with acidic species may notablyadsorb NH3, which is released from soils and domestic animalexcrements. The acidic gases in the atmosphere (e.g., HNO3,H2SO4, RCOOH) can react with NH3, and this will lead to theformation of fine particulate nitrate complexes.

The temporal variation of δ15N is presented in Fig. 9 (bot-tom panel). It is clear that δ15N exhibits a significant differ-ence between two seasons. During winter, δ15N values wereregularly higher (24.0±1.6 and 24.6±1.5‰ for day and night,respectively) than those during summer (17.0±3.7 and 16.3±2.0‰ for day and night, respectively). The greater δ15Nvalues during winter indicate an influence of residual materialfrom combustion of vegetation (Turekian et al. 1998). Themost common household cooking fuel, i.e., cow dung collect-ed from Chennai, India has an average isotope value of 14.3‰ (Pavuluri et al. 2010). From the samples collected overPiracicaba and the Amazon Basin, Brazil, Martinelli et al.(2002) reported δ15N values ranging from 8.3 to 18.7‰,where biomass burning and forest fires are very commonaerosol sources.

The particles originated from combustion of natural gasshow isotope ratios ranging from 3.0 to 15.4‰. In contrast,the particles emitted from the combustion of fossil fuels (un-leaded gasoline, diesel, fuel oil) show depletion in their iso-tope ratios. For anthropogenically influenced site in Paris(mainly fossil fuel combustion), Widory (2007) reported asimilar range of δ15N values (with mean values of 10±3.4‰in winter and 10.4±3.4‰ in summer), which are comparableto Nainital during the summer season. The lighter δ15N valuesmay also indicate the entrainment of more fresh aerosols to the

Fig. 8 A pie diagram showingthe relative contribution of watersoluble organic matter (WSOM)and water insoluble organicmatter (WIOM) along with othermajor inorganic ions in aerosolsamples collected at Nainital,India

Environ Sci Pollut Res

sampling site during summer season. Nevertheless, the latterpart of samples during summer was characterized by greaterδ15N values, which are comparable to those during winter andmay have significant biomass burning influence. The contri-bution of agriculture and residential sector includes emissionsarising from animal manure and biomass burning (agriculturalcrop residue, dung cakes, and fuel wood), which are commonover the region.

Excellent correlation (R2=0.91) was obtained betweenmass concentrations of TN and TC in winter, implying similarsources of TN and TC. However, in summer a weaker corre-lation (R2=0.34) was observed for TN and TC. Mass concen-tration ratios of TC/TN were found to be 7.8 to 20.7 with anaverage of 11.9 during winter season, whereas during sum-mer, the ratios were slightly higher (5.3 to 23.2, av. 12.7). Theannual average ratio (12.4±4.6) of TC/TN over Nainital is

higher than that over many Indian cities, but very much com-parable to the fuel wood and crop residue burning (Agnihotriet al. 2011). However, poor correlations (R2=0.11) were ob-served between TN and δ15N throughout the observation pe-riod. This suggests that the atmospheric loading of particulatenitrogen has insignificant effect on δ15N isotope ratios; in-stead, they largely depend on the type of sources and atmo-spheric processes (Freyer 1978).

Figure 11 shows the compositions of isotopic nitrogen(δ15N) for its potential sources. Data with range or mean (in-cluding standard deviation) were taken from the available lit-erature. The δ15N values for biomass burning sources (e.g.,Piracicaba and Amazon Basin, Brazil) are higher and are com-parable to those during winter over Nainital. On the contrary,the particles emitted from combustion of fossil fuels such asunleaded gasoline, diesel, and fuel oil show smaller δ15N ra-tios. The data from several urban locations, where fossil fuelcombustion was expected as a dominant source, show deplet-ed δ15N isotope ratios, which are verymuch comparable to thesummer aerosols over Nainital. From the long-term studiesover a Hawaiian ecosystem, Carrillo et al. (2002) found lighterδ15N values for the air masses transported from the NorthAmerican region due to a dominant source of oxidized nitro-gen produced from vehicle exhaust.

Enhancement of organic nitrogen in summer

In aerosol particulate matter, organic nitrogen (Org-N) com-pounds might be significant including amino compounds,urea, organic nitrates, heterocyclic nitrogen compounds, ni-tro-aromatics, and humic-like substances as well asnitrogenized soot (Zhang et al. 2002). Most of these com-pounds are of anthropogenic origin and are of most interestbecause of their potential effects on particle hygroscopicity

Fig. 9 Concentrations of totalnitrogen (TN) and its isotopicratios (δ15N), along with water-soluble NH4

2+ and NO3− in

aerosol samples collected atNainital, India

Fig. 10 Correlation plots between NO3− plus NH4

+ (massconcentrations) with total nitrogen (TN) in aerosol samples collected atNainital, India

Environ Sci Pollut Res

(Saxena and Hildemann 1996). Inorganic N (Inorg-N=NH4+-

N+NO3−-N) and organic N (Org-N=TN− Inorg-N) at

Nainital were calculated, and their statistical summaries aregiven in Table 1. Daytime and nighttime concentrations ofOrg-N during winter were on average 0.30±0.39 and 0.16±0.17 μg m−3, respectively. The concentration of Org-N insummer was several folds higher (1.5±0.7 and 1.4±0.5 μg m−3 for day and night, respectively) than that duringwinter. From winter to summer, the contribution of Org-N toTN increased from 35 to 88%. Correlations of TNwith Inorg-N in aerosol samples collected at Nainital are shown inFig. 12. Interestingly, for samples during summer, Inorg-Nhad high correlation to TN (R2=0.89) than during winter(R2=0.05).

The particulate organic nitrogen is strongly dependent onthe source distributions, lifetime, and chemistry of N com-pounds as well as atmospheric transport. The lifetimes ofmany reactive N compounds in the atmosphere are quite short(in the order of few days): however, they mainly depend onseason/temperature and height (Brasseur et al. 1999). The life-time of NOx could be less than a day in the boundary layer:however, it may persist for several days in the upper tropo-sphere. Some of the organic nitrates, organic acids, amino

acids, etc. may have lifetimes of 4 to 7 days in the free tropo-sphere that eventually get transported to the remote atmo-sphere and provide a temporary reservoir of active nitrogen(Neff et al. 2002). Studies in the past have shown that thedensity of the fire spots (both agricultural-burning and forestfires) are maximum in the regions located northwest ofNainital especially during April and May with correspondinghigh Tropospheric column NO2 values (e.g., Kumar et al.2011). Hence, it is likely that the enhanced concentration ofOrg-N over the study region during summer is mainly causedby biomass burning sources. Further, it has been shown thatover the remote locations, Org-N will be depleted in 15N(Cornell et al. 1995).

Summary and conclusions

Aerosol samples collected from a high-altitude site in the cen-tral Himalayas were studied for TC and TN and their isotopiccompositions. It has been found that δ13C values of summer

Fig. 11 Nitrogen isotopic compositions (δ15N) of potential sources ofnitrogen in Nainital aerosols. Data with range or mean (includingstandard deviation) were taken from the following sources: a this study;b Agnihotri et al. 2011; c Pavuluri et al. 2010; d Widory 2007; eMartinelli et al. 2002; f Kundu et al. 2010, and g Turekian et al. 1998

Fig. 12 Correlations of total nitrogen (TN) with inorganic N (Inorg-N=NH4

+-N+NO3−-N) in aerosol samples collected at Nainital, India

Environ Sci Pollut Res

samples are slightly lower (−26.0±1.1‰) than those of wintersamples (−24.0±0.89‰). On the other hand, the δ15N valuesare characterized by large values (+24.0‰ in winter and +17.0‰ in summer). The greater isotope ratios for winter sam-ples indicate that the aerosols are more aged during winter.This may be more closely related to boundary layer dynamics.During summer, the high winds, elevated temperature, andsupplementary convection help the transport of more freshaerosols from the source regions in Indo-Gangetic Plain areasto the high lands. The contribution of biomass and coal burn-ing isotope ratios are very much similar to the values of sam-ples during winter. The biogenic sources for the samples col-lected in winter might be derived from biomass/biofuel burn-ing of C4 plants, which are very common over this region.However, summer isotope ratios were very close to vascularplants that belong to C3 plants.

Among the measured inorganic anions, SO42− was the

most abundant species for the entire study period. Duringthe winter period, the SO4

2− contribution to aerosol mass be-came maximum. A significant linear correlation between K+

andWSOC confirms that biomass burning is in fact an impor-tant source ofWSOC in the Himalayan region. The calculatedWSOM was higher during winter. On the other hand, WIOMand EC take over during summer. This indicates that otheranthropogenic sources dominate over biomass burning in thelatter season. Further, high OM/SO4 ratio and low K/EC ratiomay be possibly caused by fossil fuel combustion during thesummer.

This study indicates that the pollutants emitted from distantsources can significantly affect the regional air quality over theHimalayas under favorable meteorological conditions. For thewinter months, the observation site remains above the bound-ary layer and thus stays as a free troposphere site where theplumes due to biomass burning arrive (enriched withWSOM,SO4

2−, and K+). During the summer, the surface temperatureincreases, and conversely the boundary layer height also in-creases. Therefore, the observation site will be well below theboundary layer. The excessive ground heating and high windfollowed by additional convection make the pollutants origi-nated over the northwestern part of India to readily arrive overthe observation site. Therefore, higher concentrations of sev-eral pollutants are noticed (viz., WIOM, EC, MSA−, andNO3

−). For the northern part of the Indian subcontinent, thisstudy could provide a baseline data set. The study would alsocontribute to validating regional air quality representation andclimate-forcing models.

Acknowledgments We appreciate the financial support of a JSPS fel-lowship to PH. C. M. Pavuluri is acknowledged for his valuable discus-sion and comments. We thank the NOAA Air Resources Laboratory forthe provision of the HYSPLIT transport and dispersion model andREADY website (http://www.arl.noaa.gov/ready.html) used in thispublication.

References

Agarwal S, Aggarwal SG, Okuzawa K, Kawamura K (2010) Size distri-butions of dicarboxylic acids, ketoacids, α-dicarbonyls, sugars,WSOC, OC, EC and inorganic ions in atmospheric particles overNorthern Japan: implication for long-range transport of Siberianbiomass burning and East Asian polluted aerosols. Atmos ChemPhys 10:5839–5858. doi:10.5194/acp-10-5839-2010

Aggarwal SG (2010) Recent developments in aerosol measurement tech-niques and the metrological issues, MAPAN. J Metrol Soc India25(3):163–187

Aggarwal SG, Kawamura K (2008) Molecular distributions and stablecarbon isotopic compositions of dicarboxylic acids and related com-pounds in aerosols from Sapporo, Japan: implications for photo-chemical aging during long-range atmospheric transport. JGeophys Res 113, D14301. doi:10.1029/2007JD009365

Aggarwal SG, Kawamura K (2009) Carbonaceous and inorganic compo-sition in long-range transported aerosols over northern Japan: impli-cation for aging of water-soluble organic fraction. Atmos Environ43:2532–2540

Aggarwal et al (2013) Traceability issue in PM2.5 and PM10 measure-ments, MAPAN. J Metrol Soc India 28(3):153–166. doi:10.1007/s12647-013-0073-x

Agnihotri R et al (2011) Stable carbon and nitrogen isotopic compositionof bulk aerosols over India and northern Indian Ocean. AtmosEnviron 45:2828–2835

Andreae MO et al (1990) The atmospheric sulfur cycle over the amazonbasin: 2.Wet season. J Geophys Res 95:16813–16824. doi:10.1029/JD095iD10p16813

Arimoto R et al (2004) Chemical composition of atmospheric aerosolsfrom Zhenbeiitai, China, and Gosan, South Korea, during ACE-Asia. J Geophys Res 109:D19S04. doi:10.1029/2003JD004323

Ayers GP, Gras JL (1991) Seasonal relationship between cloud conden-sation nuclei and aerosol methanesulphonate in marine air. Nature353:834–835

Barros AP, Kim G, Williams E, Nesbitt W (2004) Probing orographiccontrols in the Himalayas during the monsoon using satellite imag-ery. Nat Hazards Earth Syst Sci 4:29–51

Beegum SN et al (2009) Spatial distribution of aerosol black carbon overIndia during pre-monsoon season. Atmos Environ 43:1071–1078

Bendle JA, Kawamura K, Yamazaki K (2006) Seasonal changes in stablecarbon isotopic composition of n-alkanes in the marine aerosolsfrom the western North Pacific: implications for the source andatmospheric transport. Geochim Cosmochim Acta 70:13–26

Bendle J, Kawamura K, Yamazaki K, Niwai T (2007) Latitudinal distri-bution of terrestrial lipid biomarkers and nalkane compound-specific stable carbon isotope ratios in the atmosphere over thewestern Pacific and Southern Ocean. Geochim Cosmochim Acta71:5934–5955

Brasseur GP, Orlando JJ, Tyndall GS (1999) Atmospheric chemistry andglobal change. Oxford Univ, Press, New York, 654 pp

Brasseur G, Prinn RG, Pszenny AAP (eds) (2003) Atmospheric chemis-try in a changing world: an integration and synthesis of a decade oftropospheric chemistry research. Global change: the IGBP series.Springer, Berlin, 300 pp

Cachier H, Buat‐Ménard P, Frontugne M (1985) Source terms and sourcestrengths of the carbonaceous aerosol in the tropics. J Atmos Chem3(4):469–489. doi:10.1007/BF00053872

Cachier H, Buat-Menard MP, Fontugne M, Chesselet R (1986) Long-range transport of continentally-derived particulate carbon in themarine atmosphere: evidence from stable carbon isotope studies.Tellus Ser B Chem Phys Meteorol 38:161–177

Carrillo JH, Hastings MG, Sigman DM, Huebert BJ (2002) Atmosphericdeposition of inorganic and organic nitrogen and base cations in

Environ Sci Pollut Res

Hawaii. Glob Biogeochem Cycles 16(4):1076. doi:10.1029/2002GB001892

Chebbi A, Carlier P (1996) Carboxylic acids in the troposphere, occur-rence, sources, and sinks: a review. Atmos Environ 30:4233–4250

Clarke AD et al (2002) INDOEX aerosol: a comparison and summary ofchemical, microphysical, and optical properties observed from land,ship, and aircraft. J Geophys Res 107(D19):8033. doi:10.1029/2001JD000572

Cong Z et al (2010) Elemental and individual particle analysis of atmo-spheric aerosols from high Himalayas. Environ Monit Assess 160:323–335

Cornell S, Rendell A, Jickells T (1995) Atmospheric inputs of dissolvedorganic nitrogen to the oceans. Nature 376:243–246

Dumka UC, Krishna Moorthy K, Kumar R, Hegde P, Sagar R, Pant P,Singh N, Babu SS (2010) Characteristics of aerosol black carbonmass concentration over a high altitude location in the centralHimalayas from multi-year measurements. Atmos Res 96:510–521. doi:10.1016/j.atmosres.2009.12.010

Falkovich AH, Grabber ER, Schokolnik G, Rudich Y, Maenhaut W,Artaxo P (2005) Low molecular weight organic acids in aerosolparticles from Rondonia, Brazil, during the biomass-burning, tran-sition and wet periods. Atmos Chem Phys 5:781–797

Fisseha R et al (2009) Determination of primary and secondary sources oforganic acids and carbonaceous aerosols using stable carbon iso-topes. Atmos Environ 43:431–437

Flanagan LB, Ehleringer JR, Pataki DE (eds) (2005) Stable isotopes andbiosphere atmosphere interactions: process and biological controls.Elsevier Academic Press, San Diego, 318 pp

Freyer HD (1978) Preliminary 15N studies on atmospheric nitrogenoustrace gases. Pure Appl Geophys 116:393–404

Galloway JN (1995) Acid deposition: perspectives in time and space.Water Air Soil Pollut 85:15–24

Galloway JN (2000) Nitrogen mobilization in Asia. Nutr CyclAgroecosyst 57:1–12

Garg A, Shukla PR, Bhattacharya S, Dadhwal VK (2001) Sub-region(district) and sector level SO2 and NOxemissions for India: assess-ment of inventories and mitigation flexibility. Atmos Environ 35:703–713

Gelencser A (2004) Carbonaceous aerosol, Atmospheric and oceano-graphic sciences library, vol 30. Springer, Netherlands, p 350

Goyal P, Sidhartha (2002) Effect of winds on SO2 and SPM concentrationin Delhi. Atmos Environ 36:2925–2930

Grosjean D (1984) Photooxidation of methyl sulfide, ethyl sulfide, andmethanethiol. Environ Sci Technol 18(6):460–468

Gupta A, Kumar R, Kumari KM, Srivastava SS (2003) Measurement ofNO2, HNO3, NH3 and SO2 and related particulate matter at a ruralsite in Rampur, India. Atmos Environ 37:4837–4846

Habib G et al (2004) New methodology for estimating biofuel consump-tion for cooking: atmospheric emissions of black carbon and sulfurdioxide from India, Global Biogeochem. Cycles 18, GB3007. doi:10.1029/2003GB002157

Hagler GSW, Bergin MH, Smith EA, Dibb JE (2007) A summer timeseries of particulate carbon in the air and snow at Summit,Greenland. J Geophys Res 112, D21309. doi:10.1029/2007JD008993

Hegde P, Kawamura K (2012) Seasonal variations of water-soluble or-ganic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in central Himalayan aerosols. Atmos Chem Phys 12:6645–6665

Ho KF et al (2006) Variability of organic and elemental carbon, water-soluble organic carbon, and isotopes in Hong Kong. Atmos ChemPhys 6:4569–4576

Huang L et al (2006) Stable isotope measurements of carbon fractions(OC/EC) in airborne particulate: a new dimension for source char-acterization and apportionment. Atmos Environ 40:2690–2705

Huang RJ et al (2014) High secondary aerosol contribution to particulatepollution during haze events in China. Nature 514:218–222

Jung J, Kawamura K (2011) Springtime carbon episodes at Gosan back-ground site revealed by total carbon, stable carbon isotopic compo-sition, and thermal characteristics of carbonaceous particles. AtmosChem Phys 11:10911–10928

Jung J, Tsatsral B, Kim YJ, Kawamura K (2010) Organic and inorganicaerosol compositions in Ulaanbaatar, Mongolia, during the coldwinter of 2007 to 2008: dicarboxylic acids, ketocarboxylic acids,and α-dicarbonyls. J Geophys Res 115, D22203. doi:10.1029/2010JD014339

Kawamura K et al (2004) Organic and inorganic compositions of marineaerosols from East Asia: seasonal variations of water-soluble dicar-boxylic acids, major ions, total carbon and nitrogen, and stable CandN isotopic composition, Geochemical Investigation in Earth andSpace Science, A Tribute to Issac R. Kaplan, edited by R. J. Hill.Geol Soc Aust Spec Publ 9:243–265

Kolaltis LN et al (1989) Determination of methanesulfonic acid and non-sea-salt sulfate in single marine aerosol particles. Environ SciTechnol 23:236–240

Krueger BJ, Grassian VH, Laskin A, Cowin JP (2003) The transforma-tion of solid atmospheric particles into liquid droplets through het-erogeneous chemistry: laboratory insight into the processing of cal-cium containing mineral dust aerosol in the troposphere. GeophysRes Lett 30:1148. doi:10.1029/2002GL016563

Kumar R et al (2011) Influences of the springtime northern Indian bio-mass burning over the central Himalayas. J Geophys Res 116,D19302. doi:10.1029/2010JD015509

Kundu S, Kawamura K, Lee M (2010) Seasonal variation of the concen-trations of nitrogenous species and their nitrogen isotopic ratios inaerosols at Gosan, Jeju Island: implications for atmospheric process-ing and source changes of aerosols. J Geophys Res 115, D20305.doi:10.1029/2009JD013323

Lacaux JP, Artaxo P (2003) DEBITS: past, present and future. IGACactivities Newsletter 27:1–5

Lamb B, Westberg H, Allwine G, Bamesberger L, Guenther A (1987)Measurement of biogenic sulfur emissions from soils and vegeta-tion: application of dynamic enclosure methods with natusch filterand GC/FPD analysis. J Atmos Chem 5:469–491

Lee Y-N et al (2003) Air borne measurement of inorganic ionic compo-nents of fine aerosol particles using the particle-into liquid samplercoupled to ion chromatography technique during ACE-Asia andTRACE-P. J Geophys Res 108(D23):8646. doi:10.1029/2002JD003265

Li J et al (2011) Chemical composition and size distribution of wintertimeaerosols in the atmosphere of Mt. Hua in central China. AtmosEnviron 45:1251–1258

Lim YB, Tan Y, Perri MJ, Seitzinger SP, Turpin BJ (2010) Aqueouschemistry and its role in secondary organic aerosol (SOA) forma-tion. Atmos Chem Phys 10:10521–10539

López‐Veneroni D (2009) The stable carbon isotope composition ofPM2.5 and PM10 in Mexico City Metropolitan area air. AtmosEnviron 43:4491–4502

Lukács H et al (2009) Quantitative assessment of organosulfates in sizesegregated rural fine aerosol. Atmos Chem Phys 9:231–238

Malm WC, Sisler JF, Huffman D, Eldred RA, Cahill TA (1994) Spatialand seasonal trends in particle concentration and optical extinctionin the United States. J Geophys Res 99:1347–1370

Martinelli LA, Camargo PB, Lara LBLS, Victoria RL, Artaxo P (2002)Stable carbon and nitrogen isotopic composition of bulk aerosolparticles in a C4 plant landscape of southeast Brazil. AtmosEnviron 36:2427–2432

Mayol-Bracero OL et al (2002) Water-soluble organic compounds inbiomass burning aerosols over Amazonia 2. Apportionment of thechemical composition and importance of the polyacidic fraction. JGeophys Res 107(D20):8091. doi:10.1029/2001JD000522

Environ Sci Pollut Res

Mehta B, Venkataraman C, BhushanM, Tripathi SN (2009) Identificationof sources affecting fog formation using receptor modeling ap-proaches and inventory estimates of sectoral emissions. AtmosEnviron 43:1288–1295

Meinardi S, Simpson IJ, Blake NJ, Blake DR, Rowland FS (2003)Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) emissionsfrom biomass burning in Australia. Geophys Res Lett 30(9):1454.doi:10.1029/2003GL016967

Mikolajczuk A, Berglund M, Geypens B, Taylor P (2008) Carbon andnitrogen isotopic ratio of the water-insoluble fraction in air filterparticulate matter, JRC scientific and technical report, No. 45492,pp. 14

Miyazaki Y, Fu PQ, Kawamura K, Mizoguchi Y, Yamanoi K (2012)Seasonal variations of stable carbon isotopic composition and bio-genic tracer compounds of water-soluble organic aerosols in a de-ciduous forest. Atmos Chem Phys 12:1367–1376

Mori I, Nishikawa M, Iwasaka Y (1998) Chemical reaction during thecoagulation of ammonium sulphate and mineral particles in the at-mosphere. Sci Total Environ 224(1–3):87–91

Naja M, Akimoto H, Staehelin J (2003) Ozone in background and pho-tochemically aged air over central Europe: analysis of long-termozonesonde data from Hohenpeissenberg and Payerne. J GeophysRes 108(D2):4063. doi:10.1029/2002JD002477

NarukawaM,Kawamura K, Takeuchi N, Nakajima T (1999) Distributionof dicarboxylic acids and carbon isotopic compositions in aerosolsfrom 1997 Indonesian forest fires. Geophys Res Lett 26:3101–3104.doi:10.1029/1999GL010810

Neff JC, Holland EA, Dentener FJ, McDowell WH, Russell KM (2002)The origin, composition and rates of organic nitrogen deposition: amissing piece of the nitrogen cycle? Biogeochemistry 57(58):99–136

Niranjan K, Sreekanth V, Madhavan BL, Krishna Moorthy K (2006)Wintertime aerosol characteristics at a north Indian site Kharagpurin the Indo-Gangetic plains located at the outflow region into Bay ofBengal. J Geophys Res 111, D24209. doi:10.1029/2006JD007635

Novakov T, Corrigan CE (1996) Cloud condensation nucleus activity ofthe organic component of biomass smoke particles. Geophys ResLett 23:2141–2144. doi:10.1029/96GL01971

Novakov T, Penner JE (1993) Large contribution of organic aerosols tocloud condensation nuclei concentrations. Nature 365:823–826

Novakov T, Andreae MO, Gabriel R, Kirchstetter TW, Mayol-BraceroOL, Ramanathan V (2000) Origin of carbonaceous aerosols over thetropical Indian ocean: biomass burning or fossil fuels? Geophys ResLett 27(24):4061–4064

Olivier JGJ, Bouwman AF, Van der Hoek KW, Berdowski JJM (1998)Global air emission inventories for anthropogenic sources of NOx,NH3 and N2O in 1990. Environ Pollut 102(S1):135–148

Ooki A, Uematsu M (2005) Chemical interactions between mineral dustparticles and acid gases during Asian dust events. J Geophys Res110, D03201. doi:10.1029/2004JD004737

Ortiz R et al (2008) Climate change: can wheat beat the heat? AgricEcosyst Environ 126:46–58

Pant P et al (2006) Aerosol characteristics at a high-altitude location incentral Himalayas: optical properties and radiative forcing. JGeophys Res 111, D17206. doi:10.1029/2005JD006768

Pavuluri CM, Kawamura K, Tachibana E, Swaminathan T (2010)Elevated nitrogen isotope ratios of tropical Indian aerosols fromChennai: implication for the origins of aerosol nitrogen in Southand Southeast Asia. Atmos Environ 44:3597–3604

Pavuluri CM, Kawamura K, Swaminathan T, Tachibana E (2011) Stablecarbon isotopic compositions of total carbon, dicarboxylic acids andglyoxylic acid in the tropical Indian aerosols: implications forsources and photochemical processing of organic aerosols. JGeophys Res 116, D18307. doi:10.1029/2011JD015617

Pichlmayer F, Schöner W, Seibert P, Stichler W, Wagenbach D (1998)Stable isotope analysis for characterization of pollutants at high el-evation alpine sites. Atmos Environ 32:4075–4085

Puxbaum H, Tenze-Kunit M (2003) Size distribution and seasonal varia-tion of atmospheric cellulose. Atmos Environ 37:3693–3699

Rastogi N, Sarin MM (2005) Long-term characterization of ionic speciesin aerosols from urban and high-altitude sites in western India: roleof mineral dust and anthropogenic sources. Atmos Environ 39:5541–5554

Reddy MS, Venkataraman C (1999) Direct radiative forcing from anthro-pogenic carbonaceous aerosols over India. Curr Sci 76(7):1005–1011

Roberts GC, Artaxo P, Zhou J, Swietlicki E, Andreae MO (2002)Sensitivity of CCN spectra on chemical and physical properties ofaerosol: a case study from the Amazon Basin. J Geophys Res107(D20):8070. doi:10.1029/2001JD000583

Ruellan S, Cachier H (2000) Characterisation of fresh particulate vehic-ular exhausts near a Paris high flow road. Atmos Environ 35:453–468

Sagar R, Kumar B, Dumka UC, Moorthy KK, Pant P (2004)Characteristics of aerosol spectral optical depths over ManoraPeak: a high altitude station in the central Himalayas. J GeophysRes 109, D06207. doi:10.1029/2003JD003954

Salam A, Bauer H, Kassin K, Ullah SM, Puxbaum H (2003) Aerosolchemical characteristics of a mega-city in Southeast Asia (Dhaka–Bangladesh). Atmos Environ 37:2517–2528

Sarangi Tet al (2014) First simultaneousmeasurements of ozone, CO andNOy at a high altitude regional representative site in the centralHimalayas. J Geophys Res 119(3):1592–1611. doi:10.1002/2013JD020631

Satheesh SK (2012) Atmospheric chemistry and climate. Curr Sci 102(3):426–439

Saxena P, Hildemann LM (1996) Water-soluble organics in atmosphericparticles—a critical review of the literature and application of ther-modynamics to identify candidate compounds. J Atmos Chem24(1):57–109

Saxena KG, Ramakrishnan PS (1984) C3/C4 species distribution amongherbs following slash and burn in north-eastern India. ActaOecologica Oecologia Plantarum 5(4):335–346

Schefub E, Ratmeyer V, Stuut J-BW, Jansen JHF, Sinninghe Damsté JS(2003) Carbon isotope analysis of nalkanes in dust from the loweratmosphere over the central eastern Atlantic. Geochim CosmochimActa 67:1757–1767

Sharma SK et al (2010) Seasonal variability of ambient NH3, NO, NO2

and SO2 over Delhi. J Environ Sci 22(7):1023–1028Smith FA, Freeman KH (2006) Influence of physiology and climate on

δD of leaf wax n-alkanes from C3 and C4 grasses. GeochimCosmochim Acta 70:1172–1187

Stein O, Rudolph J (2007) Modeling and interpretation of stable carbonisotope ratios of ethane in global chemical transport models. JGeophys Res 112, D14308. doi:10.1029/2006JD008062

Stohl A, Koffi NE (1998) Evaluation of trajectories calculated fromECMWF data against constant volume balloon flight duringETEX. Atmos Environ 24:4151–4156

Sun Y et al (2010) Asian dust over northern China and its impact on thedownstream aerosol chemistry in 2004. J Geophys Res 115,D00K09. doi:10.1029/2009JD012757

Takahashi Y et al (2008) Observation of transformation of calcite togypsum in mineral aerosols by Ca K-edge X-ray absorption near-edge structure (XANES). Atmos Environ 42:6535–6541

Tang Y et al (2004) Three-dimensional simulations of inorganic aerosoldistribution in east Asia during spring 2001. J Geophys Res 109,D19S23. doi:10.1029/2003JD004201

Tare V et al (2006) Measurements of atmospheric parameters duringIndian Space Research Organization Geosphere BiosphereProgram Land Campaign II at a typical location in the GangaBasin: 2. Chemical properties. J Geophys Res 111, D23210. doi:10.1029/2006JD007279

Environ Sci Pollut Res

Turekian VC, Macko S, Ballentine D, Swap RJ, Garstang M (1998)Causes of bulk carbon and nitrogen isotopic fractionations in theproducts of vegetation burns: laboratory studies. Chem Geol 152:181–192

Turekian VC, Macko SA, Keene WC (2003) Concentrations, isotopiccompositions, and sources of size‐resolved, particulate organic car-bon and oxalate in near‐surfacemarine air at Bermuda during spring.J Geophys Res 108(D5):4157. doi:10.1029/2002JD002053

Turpin BJ, Huntzicker JJ (1991) Secondary formation of organic aerosolin the Los Angeles Basin: a descriptive analysis of organic andelemental carbon concentrations. Atmos Environ 25:207–215

Turpin BJ, Lim H-J (2001) Species contributions to PM2.5 mass concen-trations: revisiting common assumptions for estimating organicmass. Aerosol Sci Technol 35(1):602–610

Urban RC et al (2012) Use of levoglucosan, potassium, and water-solubleorganic carbon to characterize the origins of biomass-burning aero-sols. Atmos Environ 61:562–569

Venkataraman C, Reddy CK, Josson S, Reddy MS (2002) Aerosol sizeand chemical characteristics atMumbai, India, during the INDOEX-IFP (1999). Atmos Environ 36(12):1979–1991

Venkataraman C et al (2006) Emissions from open biomass burning inIndia: integrating the inventory approach with high-resolutionModerate Resolution Imaging Spectroradiometer (MODIS) active-fire and land cover data. Glob BiogeochemCycles 20, GB2013. doi:10.1029/2005GB002547

Wang H, Kawamura K, Shooter D (2005) Carbonaceous and ionic com-ponents in wintertime atmospheric aerosols from two New Zealandcities: implications for solid fuel combustion. Atmos Environ 39:5865–5875

Wang X et al (2012) The secondary formation of inorganic aerosols in thedroplet mode through heterogeneous aqueous reactions under hazeconditions. Atmos Environ 63:68–76

Widory D (2007) Nitrogen isotopes: tracers of origin and processes affectingPM10 in the atmosphere of Paris. Atmos Environ 41:2382–2390

Widory D et al (2004) The origin of atmospheric particles in Paris: a viewthrough carbon and lead isotopes. Atmos Environ 38:953–961

Yadav S, Rajamani V (2004) Geochemistry of aerosols of northwesternpart of India adjoining the Thar desert. Geochim Cosmochim Acta68(9):1975–1988

Yamamoto S, Kawamura K, Seki O, Kariya T, Lee M (2013) Influence ofaerosol source regions and transport pathway on δD of terrestrialbiomarkers in atmospheric aerosols from the East China Sea.Geochim Cosmochim Acta 106:164–176

Zhang Q, Anastasio C, Jimenez-Cruz M (2002) Water-soluble organicnitrogen in atmospheric fine particles (PM2.5) from northernCalifornia. J Geophys Res 107(D11):4112. doi:10.1029/2001JD000870, 2002

Ziemba LD, Fischer E, Griffin RJ, Talbot RW (2007) Aerosol acidity inrural New England: temporal trends and source region analysis. JGeophys Res 112, D10S22. doi:10.1029/2006JD007605

Environ Sci Pollut Res