elemental carbon distribution in svalbard snow

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/,

Elemental carbon distribution in Svalbard snow

S. Forsstrom1, J. Strom

2, 1, C. A. Pedersen

1, E. Isaksson

1and S. Gerland

1

S. Forsstrom, Norwegian Polar Institute, Polar Environmental Centre, 9296 Tromsø, Norway.

([email protected])

1Norwegian Polar Institute, Tromsø,

Norway

2Department of Applied Environmental

Science, Stockholm University, Stockholm,

Sweden.

D R A F T May 27, 2009, 3:27pm D R A F T

X - 2 FORSSTRM ET AL.: ELEMENTAL CARBON DISTRIBUTION IN SVALBARD SNOW

Abstract.

The concentration of apparent elemental carbon (ECa, based on a thermal-

optical method) in the snow was investigated in Svalbard (European Arc-

tic), during spring 2007. The median ECa-concentration of 81 samples was

4.1 µgl−1 and the values ranged from 0 to 80.8 µgl−1 of melt water. The me-

dian concentration is nearly an order of magnitude lower than the previously

published data of equivalent black carbon (BCe, based on an optical method),

obtained from Svalbard snow in the 1980s. A systematic regional difference

was evident: ECa concentrations were higher in East-Svalbard compared to

West-Svalbard. The observations of snow ECa cover spatial scales up to sev-

eral hundred kilometers, which is comparable to the resolution of many cli-

mate models. Measurements of atmospheric carbonaceous aerosol (2002–2008)

at Zeppelin station in Ny-Alesund, Svalbard, were divided to air mass sec-

tors based on calculated back-trajectories. The results show that air origi-

nating from the eastern sector contains more than two and half times higher

levels of soot than air arriving from South-West. The observed East-West

gradient of ECa-concentrations in snow may be due to a combination of the

atmospheric concentration gradient, the orographic effect of the archipelago,

and the efficient scavenging of the carbonaceous particles through precipi-

tation.


FORSSTRM ET AL.: ELEMENTAL CARBON DISTRIBUTION IN SVALBARD SNOW X - 3

1. Introduction

Carbonaceous aerosol particles are emitted from both natural (forest fires) and anthro-

pogenic (biomass and fossil fuel burning) combustion sources. These particles, often called

soot, cause a net positive climate forcing (Forster et al. [2007], Hansen and Nazarenko

[2004], Jacobson [2002]). The forcing is due to light absorption by the particles, which

lowers the surface albedo on snow and ice covered areas (Hansen and Nazarenko [2004])

and heats the atmosphere via three mechanisms: the direct effect (e.g., Schulz et al.

[2006], Chylek and Wong [1995]), the indirect effect (e.g., Hansen et al. [1997]), and the

semi-direct-effect (e.g., Johnson [2003]).

Model calculations suggest a 10% reduction of the spectraly averaged albedo for soot

content of about 1000 µgl−1 for fresh snow (grain radius 0.1 mm). For old melting snow

(grain radius 1 mm) a soot concentration one fifth of that is needed for 10% albedo

reduction. (Warren and Wiscombe [1985]) The small initial darkening of the snow speeds

up the grain growth and the melt, which leads to further albedo reduction. The largest

forcing coincides with the onset of spring melt (Flanner et al. [2007]). Together with

several other features, such as the increase of the absortion by soot as a function of snow

grain size (Warren and Wiscombe [1980]), this leads to positive feedbacks. The result

is a climatic forcing with high efficacy (Flanner et al. [2007], Hansen and Nazarenko

[2004]). However, there are large gaps in understanding the transport and deposition

of carbonaceous aerosol particles to the Arctic snow pack. Also, the above mentioned

modeling results remain to be verified by in-situ measurements.



Carbon dioxide, with long atmospheric lifetime, is the cause for most of the human-

induced warming (Forster et al. [2007]). However, short-lived pollutants, like soot, have

drawn both scientific and political interest because a reduction of these emissions would

result in much faster lowering of their climate forcing (Quinn et al. [2007]).

The previous soot measurements in the Arctic snow pack are few and mainly from the

1980s (Table 1, See Flanner et al. [2007] for more complete listing). The objective of

this work is to study the present-day carbonaceous aerosol particle distribution in snow

in Svalbard, and compare these findings to concentrations measured in the air.

The atmospheric transport of soot to Svalbard was studied by connecting atmospheric

soot measurements to back-trajectory calculations, in order to understand the observed

regional (∼ 100 km) scale variability in the snow pack.

2. Data collection and methods

2.1. Field area and snow sampling

Svalbard is situated between 74 and 81 degrees North in the European sector of the

Arctic (Figure 1). The archipelago, 60% of which are covered by ice (Hagen et al. [2003]), is

well suited for studies of long-distance transport and deposition processes as local sources

are few and essentially limited to the settlements Longyearbyen (c. 2000), Barentsburg

(c. 500), Svea (c. 250), Polska Stacja Polarna in Hornsund (c. 8–25) and Ny-Alesund (c.

40–150 inhabitants) (Figure 1). A trajectory climatology study (Eneroth et al. [2003]),

atmospheric measurements (Stohl et al. [2007], Staebler et al. [1999]), and snow- and

ice core studies (Hicks and Isaksson [2006], Hermanson et al. [2005]) confirm that long-

distance transport of pollutants from lower latitudes reaches Svalbard.



The cyclonic activity over the Norwegian Sea, combined with orographic lifting of the

air masses, brings more precipitation to Svalbard than to the generally dry surrounding

Arctic. During precipitation the main wind direction is from east or south-east, which are

expected to be the main directions for the air pollution transport (Semb et al. [1984]).

The eastern parts of the archipelago are known to have the highest precipitation due

to the easterly winds produced by the low pressure systems traveling over the Barents

Sea region, south of Svalbard (Hisdal [1976]). The melt season on the Svalbard ice caps

starts between late May and late June and ends between late August and the beginning

of October (Sharp and Wang [2009]). The areas north and east from Svalbard is covered

with sea ice a major part of the year.

Eighty-one samples from the winter snow pack were collected during several field cam-

paigns in February–April 2007. At each of the seven field sites (Figure 1, Table 2) 5–12

samples were collected, apart from the Brøggerhalvøya (Ny-Alesund) area where a more

extensive sampling was conducted (39 samples). The campaign concentrated on surface

samples (typically down to 5 cm depth), but at most of the sites the whole seasonal snow

column below was sampled. At Holtedahlfonna, Kongsvegen, Linnebreen, Lomonosov-

fonna and Austfonna the samples were taken on glaciers, while on Brøggerhalvøya and in

Inglefieldbukta samples collected on tundra and landfast sea ice were included.

2.2. Instrumentation and sample analysis

The snow was collected in glass jars, melted at room temperature, and filtered through

quartz microfiber substrates. The Thermal/Optical Carbon Aerosol Analyzer (Sunset

Laboratory Inc., Forest Grove, USA), and the NIOSH 5040 protocol (Birch [2003]), were

employed to obtain apparent elemental carbon (ECa) concentrations in the snow. (Here-



inafter the bracket notation for the mass concentrations is used, e.g., [ECa].) The carbon

collected on the filter is divided into apparent organic (OC) (including carbonate (CC))

and elemental (ECa) carbon depending on its volatilization temperature. First, a punch

of typically 1 cm2 cut from the filter is heated to 860 ◦C in a He-atmosphere for releasing

OC and CC. In the second stage of the analysis ECa is released by heating of the filter

substrate in an oxygen-helium atmosphere. The released CO2 is reduced to CH4 for de-

tection by a flame ionization detector (FID). The transmittance of the filter is monitored

optically using laser light, which allows the correction for pyrolysis (charring) occurring

during the analysis. The apparent elemental carbon, ECa, is used as a proxy for the light

absorbing carbonaceous aerosol.

The atmospheric soot sampling and measurements are conducted at the station Zeppelin

(78 ◦54′ N 11 ◦53′ E, 474 m.a.s.l.) near Ny-Alesund, Svalbard (Fig. 1), using a filter based

optical method. A custom built particle soot absorption photometer (PSAP) based on the

integrating plate technique, is employed. The outcome of the measurement, equivalent

black carbon (BCe), is another widely used proxy for the light absorbing part of the

carbonaceous aerosol. PSAP employs a LED (light-emitting diode) with a wavelength of

530 nm to illuminate two 3 mm diameter spots on a substrate (Tissuglass). The particles

are collected from the air by flushing it through the filter, keeping one of the spots clean

for reference. The evolution of the filter transmittance is measured in order to derive the

light extinction coefficient of the loaded filter.

As light extinction is the sum of absorption and scattering, a correction for the scat-

tering is needed to obtain an estimate of the absorption coefficient (babs) of the loaded

filter. Also, the effect that the filter loading has on the extinction needs to be taken



in consideration. Both corrections were done following Bond et al. [1999]. Data from a

TSI 3563 Nephelometer was used for the correction for the light scattering particles. No

adjustment was done for the small difference in wavelength between the Nephelometer

(550 nm) and PSAP (530 nm) instruments. For details of the correction scheme used for

PSAP, see Krecl [2008]. To convert babs to mass concentration a specific absorption cross

section (σabs) of 10 m2g−1 was used.

2.3. Trajectory analysis

Atmospheric back-trajectories were used to estimate the origin of the air. Trajecto-

ries give a better picture of the atmospheric transport paths than locally measured wind

direction especially at locations like Svalbard, where the topography strongly influences

the wind pattern. The NOAA HYbrid Single-Particle Lagrangian Integrated Trajectory

model (HYSPLIT) (Draxler and Rolph [2003]) was used for back-trajectory runs for the

measurement period 2002–2008 calculating seven-day back-trajectories, ending at Zep-

pelin station location and altitude. The direction of the flow was defined as the angle

of the sum vector based on the whole trajectory. Each of the vectors was linked to a

six-hour average of hourly [BCe] measurements at Zeppelin and classified into one of the

eight sectors (Fig. 2). The analysis comprising of 8359 trajectories, four for each day, are

likely to capture the characteristic features of the relation between observed atmospheric

[BCe] and airmass origin.



3. Results and discussion

3.1. ECa concentrations in the snow

The [ECa] in the snow from 86 samples (Table 2 and Figure 3) are low, as expected

for remote Arctic sites. An exception is Linnebreen, which suffers from local pollution

from the coal mining settlement Barentsburg, 15 km North-East of the sampling site (Fig.

1). The mean and median [ECa] (excluding the 5 samples from Linnebreen) calculated

by giving an equal weight to each sample are 8.7 µgl−1 and 4.1 µgl−1, with the values

ranging from 0 to 80.8 µgl−1 of meltwater. The dataset is not a complete mapping of

soot concentrations in Svalbard, since the samples were collected during different field

campaigns in spring 2007. Instead, it can be viewed as an insight into the range of

variability. The linkages between [ECa] and the sampling site altitude and depth of the

sample in the snow pack, were studied, but no evident correlation could be found.

A spatial difference in snow soot concentrations on the regional scale of 10–100 km

(scales similar to scales resolved in climate models) was found. The medians of the ECa

samples from the eastern and western parts of the archipelago were compared by applying

the Kruskal-Wallis-test (Kruskal and Wallis [1952]). Brøggerhalvøya, Holtedahlfonna,

and Kongsvegen were defined as western sites, and Austfonna, Lomonosovfonna, and

Inglefieldbukta as eastern sites (Fig. 1). Linnebreen was left out of the comparison.

The resulting p-value around 10−4 indicates that the median of the mass concentrations

measured at the eastern sites (7.3 µgl−1) was statistically larger than what was found

at the western sites (2.7 µgl−1) at a high confidence level. Especially the concentrations

measured at Inglefieldbukta enhance the median of the eastern sites. To some extent this



pattern of larger [ECa] in East-Svalbard can be seen in the modeling results of Flanner

et al. [2007] (their Fig. 5).

A concentration of 15 µgl−1 of soot in new snow reduces the spectral albedo at 470 nm

(the most sensitive wavelength) by about 1% (Warren and Wiscombe [1985]), and can

be considered a detection-threshold for spectrometers measuring albedo (Grenfell et al.

[2002]). However, soot is much more effective in reducing the snow albedo for larger snow

grains, as well as if the mixing between snow and soot grains is internal (Chylek et al.

[1983]). For melting old snow with large grains, only 3 µgl−1 would be needed to cause

a 1% albedo reduction. In this study, 11% of the measurements exceeded the detection-

threshold for new snow, and 63% for old snow. High concentrations were more common

at the eastern sites.

3.1.1. Variability and uncertainties

The variability caused by the sampling and analytical method was studied by taking

multiple samples from the same locations (within approximately one meter) and the same

depths (approximately the top 5 cm) for six of the sites. The combination of the natural

variability in the snow pack and the inherent uncertainties in the method caused large

variations: the relative root mean square deviation within the multiple sample sets was,

on average, 1.0.

One cause for the horizontal variability of snow impurity content at small scales is

wind induced snow drift, an event common in Svalbard (Jaedicke [2001]). The enhanced

sublimation on crystal surfaces during snow drift causes an increase in impurity concen-

trations (Pomeroy et al. [1991]), and together with the redistribution of snow, influences

the impurity concentration distribution in snow.



A systematic sampling campaign covering the same time period would be needed to

verify the East-West gradient of [ECa] in the Svalbard snow. Although the [ECa] median

from eastern Svalbard is higher than the median from western Svalbard, this result is

challenged by the limited number of samples, the heterogeneity in the sampling timing

and strategy, and the observed variability within the multiple samples. Using ECa as a

proxy for long distance transported soot might lead to an exaggerated estimate due to

the possible presence of elemental carbon -containing soil dust in the snow samples.

A possible ECa-negative artifact exists in the specific procedure used: the hydrophobic

soot particles might attach to the walls of the sample jar as soon as the snow sample is in

liquid form (Clarke and Noone [1985], Ogren et al. [1983]). The result from a laboratory

experiment (Figure 4) showed that a significant reduction in the [ECa] required storing

time longer than 1.5 days, indicating that the procedure of melting the samples in glass

jars over night did not cause large losses.

Several techniques to measure light absorbing carbonaceous aerosols exist. As all of the

techniques have their limitations, the observed concentrations are specific for the method

used. Some of the previous measurements of soot in snow are listed in Table 1. Clarke

and Noone [1985] measured [BCe] in spring of 1983, which are eight times higher than the

median [ECa] (three and half times higher than the mean [ECa]) of samples in this study.

The [BCe] measured by Grenfell et al. [2002] on the sea ice in the central Arctic in 1998

had a mean of the same magnitude as the data presented here, but with less variability.

Clarke and Noone [1985] and Grenfell et al. [2002] used an optical analysis method, while

a thermal-optical technique is used here. The methods give results which can differ up to

factor of 7, while factor of 2 differences are common (Watson et al. [2005]). The thermal-



optical analysis is expected to underestimate the light absorbing material, since a part

of the organic carbon (separated from the ECa in the thermal-optical analysis) is known

to absorb light (Andreae and Gelencr [2006]). The outcome of the optical analysis, BCe,

is, instead, the amount of the total light absorbing material on a sample filter, including

minerals and organic matter. According to Watson et al. [2005], however, the differences

between the methods are unsystematic. Advanced optical methods can separate dust

from BCe using the spectral signature of the sample filter. Due to the discrepancies in the

methods, it is not straightforward to conclude that the lower values presented here were

solely due to the reductions in the aerosol levels after the 1980’s (Husain et al. [2008],

Quinn et al. [2007]), although it may be part of the explanation.

3.2. Transport of atmospheric soot to Svalbard

The atmospheric time series of [BCe] for 2002–2008 shows that the measured concen-

trations in the air at Zeppelin are low apart from the springtime arctic haze (e.g., Stohl

[2006], Shaw [1995]) events (Fig. 5). The mean [BCe] over the 6.5 years of measurements

is 44 ngm−3, while Eleftheriadis et al. [2009] reported 39 ngm−3 for 1998–2007 at the same

site using Aethalometer. The mean [BCe] of the dataset of this study for January through

March 2002–2008 is 73 ngm−3. This value compares well with a model experiments (Koch

and Hansen [2005]) suggesting black carbon concentrations of 50–100 ngm−3 for these

months in the surface air in the Arctic. The Zeppelin station BCe-record is too short for

any meaningful trend analysis. It is anyway evident from the data that 2007 and 2008

were lower in [BCe] than the earlier years.

The measured air [BCe] depends on the transport and precipitation history of the air

mass. The trajectory sum vector calculations together with the air [BCe] data from



Zeppelin station show that air from the east contains over two and half times more BCe

than air from south-west (Fig. 6 A and Table 3). This result is in agreement with Staebler

et al. [1999], a study relating the Ny-Alesund aerosol physical and chemical properties to

their source region. Northern, northwestern and southern transport paths bring air with

similar intermediate [BCe] levels. In Figure 5 one can see the same pattern with polluted

air arriving from northeast, east and southeast.

According to the back-trajectory runs, the air at Zeppelin mountain, Ny-Alesund, ar-

rives most often from the north (23%) or northeast (21% of the trajectories). Runs when

the direction of the flow is from east (12%) and west (10% of the trajectories) are about

half as frequent. Southern flow occured for only 5% of the trajectory runs. Most of the

total carbonaceous aerosol burden arrives to Svalbard from the north and northeast (Fig.

6 B). This is due to the the northern and northeastern flows being the most frequent and

having substantial [BCe].

The high concentrations measured in the air arriving from the East and South-East

is due to the source regions, Europe and North-Asia, which produce substantial soot

emissions (Bond et al. [2004]). The cause for the low air [BCe] in the southwesterly flow

is most likely that the pollutants from North America or the North Atlantic ship traffic

are removed by precipitation in the North Atlantic storm track (Shaw [1995]) or blocked

by the high plateau of Greenland (Rahn [1981]). The [BCe]-gradient in the incoming air

does not alone cause the difference in snow [ECa] at the eastern and western sites. A

systematic scavenging of the western air at the west and the eastern air at the east coast,

due to prevailing flow directions in combination to the orographic effect of the archipelago

is a possible explanation for the observed pattern.



The [BCe] values were derived based on the specific absorption cross section (σabs) of 10

m2g−1. In the literature, values for σabs of soot vary between 1 and 30 m2g−1 depending on

the chemical composition, size and shape, and mixing state of the particles (Andreae and

Gelencr [2006]). Bond and Bergstrm [2006] reports 7.5 m2g−1 for pure soot particles. For

a remote site the particles are aged and σabs is thus expected to be somewhat higher. The

results from simultaneous ECa and BCe measurements are in good agreement (Forsstrm

[2008]), which confirms that for atmospheric measurements the two methods can be used

interchangeable (Krecl et al. [2007]) and that the value used for σabs is reasonable for this

specific site. Furthermore, the possible error from the choice of σabs doesn’t influence the

relative pattern of soot content of the air masses arriving from different directions (Fig.

6).

4. Conclusions

1. Apparent elemental carbon (ECa) concentrations from 81 snow samples taken around

Svalbard in spring 2007 are low, and show large variation at each of the 6 locations. The

samples at the eastern side present statistically significantly higher values than those at

the western side.

2. Linking the observed atmospheric equivalent black carbon BCe concentration at

the Zeppelin station, Ny-Alesund with air mass trajectories, shows that generally higher

concentrations are observed when the air comes from the east than from west. This could

be one factor to explain why the measured ECa content in snow in East-Svalbard presented

systematically higher values compared to the western side.



3. The snow ECa data in this study are, in general, lower (on average by a factor of 4)

than previous measurements of BCe from Svalbard reported by Clarke and Noone [1985].

For median values the difference is a factor of 8. Three factors contribute to the difference:

(i) the lower atmospheric soot burden today compared to the 80’s, (ii) the two different

methods for determining BCe and ECa, and (iii) loss of carbon from the samples after

collection.

Acknowledgments. This study is part of the projects Measurements of Black Carbon

aerosols in Arctic snow – interpretation of effect on snow reflectance, Climate effects of

reducing black carbon emissions and Svalbard ice cores and climate variability financed

by the Norwegian Polar Institute and the Research Council of Norway. The aerosol mea-

surements at the Zeppelin station are funded by the Swedish Environmental Protection

Agency. Part of the work was supported by The University of Helsinki Funds - The Math-

ematics and Science Fund and Nordlys exchange program. We appreciate the help from

various colleagues to collect the snow samples and the laboratory personnel in ITM to

analyse the filters. We thank Stephen Hudson (NPI) for useful comments and language

polishing.

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Figure 1. The medians of apparent elemental carbon (ECa) in µg1−1 at seven sampling

locations.

Figure 2. The division of the geographical area surrounding Svalbard to the eight sectors. The

projections of the azimuth angels from Zeppelin are plotted on a stereographical map projection.

Shoreline data from Matlab m map-package.

Figure 3. The measured apparent elemental carbon (ECa) concentrations at each site except

Linnbreen. The standard deviation from the mean (solid horizontal line) at each site is noted

with an errorbar. The square marker is the median of the subset. The sites are plotted from

west (on the left) to east.

Figure 4. A test was done for investigating the possible ECa losses as function of sample storing

time in liquid form. Snow was melted in a large plastic container, mixed well and distributed

to glass jars. The [ECa] was measured after 12, 36, 180 and 732 hours after the commencing of

the melt. Three parallel samples measured at each time step are marked with white markers.

The black squares indicate the means of the sample set and the error bars show the standard

deviations from them.

Figure 5. Time series of atmospheric equivalent black carbon (BCe) at Zeppelin station,

Ny-Alesund in 2002–2008. Concentrations in ngm−3. The light gray markers indicate flow from

northeast, east or southeast and dark gray markers flow from south, southwest or west.



Figure 6. A. Sector plot showing the connection between the measured air [BCe ] and the

direction of the flow according to the back-trajectory runs. The sectors are centered on Zeppelin

station coordinates and altitude (474 m). The number of trajectories falling into each 45 ◦ sector

is indicated by the number. The thick arc shows the median of the six-hours mean air [BCe ] on

when the mean vector of the corresponding back-trajectory falls into the sector. The innermost

arc indicates the 25 th percentile and the outermost arc the 75 th percentile of the concentration.

The axis unit is ngm−3.

B. Sector plot showing the total burden of atmospheric BCe to Svalbard. The median, 25- and 75

percentile concentrations are multiplied with the fraction of trajectories belonging to the sector

in question.



Table 1. Comparison to earlier studies. The minimum, average, and maximum values and

the standard deviation from each study are given in µgl−1.

Reference This study Clarke and Clarke and Noone and Grenfell Chylek Chylek

Noone [1985] Noone [1985] Clarke [1988] et al. [2002] et al. [1987] et al. [1995]

Site and time Svalbard, Svalbard, American and Abisko, SHEBA drift, Camp Century, Summit,

spring 2007 1983 European side Sweden, central Arctic, Greenland, Greenland,

of the Arctic, spring 1984 basing 1987 1989–90

1983–84 spring 1998

Min 0 6.7 0 2.4 1 2.1 1.4

Average 8.7 30.9 32.9 29.1 4.4 2.4 2.0

Max 80.8 52.0 127 77.1 7 2.6 2.7

Std 15.2 16.0 28.8 22.8 2.9

Filter used Quartz micro fibre Nuclepore Nuclepore Nuclepore Nuclepore

(0.4 µm) (0.4 µm) (0.4 µm) (0.4 µm)

+Millipore QA +Millipore QA

(0.45 µm) (0.45 µm)

Method Thermal-optical Optical Optical Optical Optical Thermal-optical Thermal-optical

NIOSH 5040 (4 wavelengths, (4 wavelengths, (modification (4 wavelengths, Dod et al. [1978] Dod et al. [1978]

Birch and IP+IS) IP+IS) of IP) IP+IS)

Cary [1996]

IP - Integrating Plate method , IS - Integrating Sandwich method (Lin et al. [1973], Clarke [1982].)



Table 2. The measured apparent elemental carbon (ECa) in snow at seven field sites in

Svalbard. Sampling site and its altitude, sampling date, number of samples (number of surface

samples in parenthesis) together with the mean, median, minimum, maximum, and standard

deviation of the concentrations are listed. Concentrations are in µgl−1.

Site Altitude m.a.s.l. Date #(surface) Mean Med Min Max Std

Brøggerhalvøya (10 locations) 10–438 25.03–01.04.07 39(15) 4.1 3.2 0 23.4 4.1

Kongsvegen 640 22.04.07 5(3) 2.2 1.7 0.5 6.0 2.2

Holtedahlfonna 1180 17.04.07 5(3) 2.1 1.4 0 4.8 1.8

Lomonosovfonna 1250 27.03.07 15(8) 18.8 6.6 0 80.8 29.4

Inglefieldbukta (4 locations) 0–96 25.02.–25.03.07 12(12) 13.9 9.8 2.3 41.6 11.1

Linnebreen 350 10.–11.04.07 5(3) 254.0 240.0 96.4 520.2 167.0

Austfonna 749 18.04.07 5(4) 14.0 6.5 4.1 45.2 17.6

All sites except 0–1250 25.02.–22.04.07 81(48) 8.7 4.1 0 80.8 15.2

Linnebreen

Table 3. The median and mean for six-hour mean air [BCe ] for each sector (direction of the

arriving air) shown in Fig. 6. Concentrations are in ngm−3. The percentages of trajectories

falling in to each sector are listed.

Sector % of trajectories [BCe] median [BCe] mean

North (N) 23 13.3 31.5North-East (NE) 21 16.3 55.0East (E) 12 19.5 80.4South-East (SE) 7 14.7 97.8South (S) 5 10.0 30.2South-West (SW) 8 7.5 18.3West (W) 10 10.4 21.7North-West (NW) 15 13.4 28.0


elemental carbon distribution in svalbard snow

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