Main source of Arctic soot or black carbon today is south Asia, specifically China and India. Most black carbon on Greenland is from south Asia--Hansen, Koch, NASA GISS study, Feb. 2005

"The largest contribution to BC deposited on Greenland is from south Asia."...
 
2/25/2005, "Distant origins of Arctic black carbon: A Goddard Institute for Space Studies ModelE experiment," Journal of Geophysical Research Atmospheres, Dorothy Koch and James Hansen
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"Abstract"

"[1] Black carbon (BC) particles, derived from incomplete combustion of fossil fuels and biomass, may have a severe impact on the sensitive Arctic climate, possibly altering the temperature profile, cloud temperature and amount, the seasonal cycle, and the tropopause level and accelerating polar ice melting. We use the Goddard Institute for Space Studies general circulation model to investigate the origins of Arctic BC by isolating various source regions and types. The model suggests that the predominant sources of Arctic soot today are from south Asia (industrial and biofuel emissions) and from biomass burning. These are the primary global sources of BC (approximately 20% and 55%, respectively, of the global emissions), and BC aerosols in these regions are readily lofted to high altitudes where they may be transported poleward. According to the model the Arctic BC optical thickness is mostly from south Asia (30%) and from biomass (28%) (with slightly more than half of biomass coming from north of 40°N); North America, Russia, and Europe each contribute 10–15%. Russia, Europe, and south Asia each contribute about 20–25% of BC to the low-altitude springtime “Arctic haze.” In the Arctic upper troposphere/lower stratosphere during the springtime, south Asia (30–50%) and low-latitude biomass (20–30%) are dominant, with a significant aircraft contribution (10–20%). Industrial S emissions are estimated to be weighted relatively more toward Russia and less toward south Asia (compared with BC). As a result, Russia contributes the most to Arctic sulfate optical thickness (24%); however, the south Asian contribution is also substantial (17%). Uncertainties derive from source estimates, model vertical mixing, and aerosol removal processes. Nevertheless, our results suggest that distant sources contribute more to Arctic pollution than is generally assumed."
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"1. Introduction"

"2] The Arctic is a particularly sensitive region to global climate change....Changes in Arctic chemistry and influx of pollution may disrupt this sensitive system [e.g., Rinke et al., 2004]. We do not attempt to address the complex web of dynamical and radiative influences. Our focus is on black carbon aerosols in the Arctic as we attempt to discern its origins.

[3] Black carbon (BC), which is the absorbing portion of carbonaceous aerosols, commonly called “soot,” is derived from the incomplete combustion of fossil fuels (primarily coal and diesel) and from the burning of biomass or biofuels. Globally it may contribute to climate warming, with recent radiative forcing estimates of +0.55 W m² [Jacobson, 2001] or higher if various indirect effects are considered [e.g., Hansen and Sato, 2001; Hansen et al., 2002]. BC has been implicated in previous studies as potentially disrupting Arctic climate. Clarke and Noone [1985] found that snow albedos are reduced by 1–3% in fresh snow and by another factor of 3 as the snow ages and the BC becomes more concentrated. Hansen and Nazarenko [2004] modeled this decreased albedo in Arctic snow and sea ice and found this resulted in a hemispheric radiative forcing of +0.3 W m⁻², which may have had a substantial impact on the Northern Hemisphere climate in recent decades. In addition, soot in the air may absorb radiation, warming the air and possibly reducing cloud formation [Ackerman et al., 2000; Hansen et al., 1997].
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[4] Most aerosols are believed to be transported to the Arctic during the winter and spring via the mostly low-altitude ‘Arctic haze’ transport events [Shaw, 1995]. Arctic haze is associated with (otherwise) clear, typically anticyclonic conditions. The haze consists primarily of particles, characterized by high sulfur concentrations and other components such as soot. At the surface, particulate concentrations are maximum during winter and springtime, due to a combination of more efficient poleward transport during these seasons and increased removal by low-level drizzling clouds in the summer [Shaw, 1995; Barrie, 1986]. Sulfate amount tends to peak slightly later in winter than black carbon, because sulfate formation depends upon photo-oxidants that become available when the polar sun rises [Hopper et al., 1994]. Rahn [1981a, 1981b] used chemical fingerprinting of the wintertime low-altitude haze to identify likely source regions. The high observed Mn/V and elevated black carbon concentrations point to Eurasia rather than North America as the likely major source area. However the North American Arctic had Mn/V too high to be attributed to either region. Rahn [1981b] suggested coal burning from central USSR as a likely source of such very high Mn/V. China and south Asia were excluded from the analysis on the basis of meteorological argument. For example, air masses from the south of Barrow (the presumed pathway for south Asian airmasses) were observed to be much cleaner than those from the north. More sophisticated analyses, using more elements [Rahn and Lowenthal, 1984; Lowenthal and Rahn, 1985; Lowenthal and Borys, 1997] and incorporating trajectory information [Cheng et al., 1993] confirmed Eurasia as the primary source of winter-spring Arctic haze. Once again China and south Asia were not included in these analyses since they were assessed to be unlikely source regions.
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[5] Meteorological conditions and backtrajectory analysis have generally supported the northern Eurasian source region of Arctic haze. The midnorthern Eurasian high, aided by cyclonic systems over the Barents Sea, steers pollution from Eurasia into the Arctic. Iversen and Joranger [1985] argued that the formation of a large isentropic dome that extends over Eurasia during winter facilitates transport of pollution poleward. However, some recent analyses leave open the possibility of south Asian pollution sources. Harris and Kahl [1994] analyzed isentropic back trajectories for 7 years of data at Barrow, Alaska. They showed that during the Arctic haze season, transport from north central Russia occurs near the surface with about 20% frequency. Less frequent (10%) transport from Europe occurs at higher altitude. Interestingly, over 30% frequency of transport originates from the North Pacific, at altitudes of 1500–3000 m. Khattatov et al. [1997], examined lidar measurements throughout the Arctic, and suggested that 5-day back trajectories typically found air masses still within the Arctic vortex rather than near their source regions. They argued that Arctic haze appears to come from aloft rather than being transported near the surface.
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[6] Chemical modeling studies [e.g., Klonecki et al., 2003; Lamarque and Hess, 2003; Stohl et al., 2002] found that although south Asia generates significant amounts pollutants such as ozone, CO and hydrocarbons, it is not an important source region to the Arctic.
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[7] Thus, on the basis of analysis of trace elements, meteorology, back trajectory and chemistry models, it appears that Eurasia (western Asia and eastern Europe) is the primary source of Arctic haze, defined to be the particulate pollution near the surface of the Arctic during winter and spring. However, when considering the origin and impacts of black carbon in the Arctic, several factors not usually included in Arctic haze studies need to be considered.
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[8] First are some of the distinct characteristics of black carbon. Most industrial and biofuel BC emissions are presently derived from south Asia [Bond et al., 2004]. BC emissions, compared with sulfate, are more heavily weighted toward south Asia. BC also has a relatively large source from tropical biomass burning, again weighting its global emissions southward. In contrast with less soluble gaseous pollutants, particulates are more likely to be deposited (mostly rained out) when they are confined to the lower troposphere, as emissions from Europe and Russia commonly are. However particles from East Asia are more readily lofted to higher altitudes where they can travel greater distances above precipitating clouds.
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[9] Thus, if these distant sources are substantial contributors to the Arctic, we would expect to find evidence in high altitude haze. Such higher altitude pollution would be less limited to the winter/spring, but would also appear later in the year. As mentioned above, Khattatov et al. [1997] inferred significant high altitude haze. If haze is derived from south Asia, one would expect it to appear in the North Pacific at high altitudes, a frequent transport pathway throughout the year [Harris and Kahl, 1994]. Several aircraft studies have reported high altitude summertime haze. For example, Brock et al. [1989] reported substantial summertime haze during August 1985 above 850 mbar over Greenland and the North American Arctic. The haze particles were primarily sulfate and soot was also present. The authors note that such summertime haze is often not visible from the surface because of the frequent presence of low-level clouds in summer. Scheuer et al. [2003] observed the progression of particulate sulfate vertical distribution from spring into summer (2000) over the North American Arctic. During early winter the haze was confined to the surface. As the season progressed surface haze diminished and high altitude haze increased. Rosen and Hansen [1984] report that BC in aircraft observations over Barrow increase by a factor of 3 above the boundary layer. Other areas of the Arctic also have distinct layers of high BC concentration, often with substantial levels in the free troposphere.
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[10] We should also bear in mind that the relative emissions from potential source regions have shifted over the course of the past 40 years, since the early investigations of Arctic haze. Novakov et al. [2003] have estimated industrial changes in BC emissions for some countries, on the basis of fuel use and limited consideration of technology change. The (former) Soviet Union (FSU) was implicated as a major source of Arctic haze in many studies. Novakov et al. [2003] found that black carbon emissions from the FSU in the late 1990s was less than 1/4 their peak levels of 1980. European emissions are also about 1/3 their levels in the 1970s. However China and India have doubled their BC emissions since the late 1970s. Thus BC emissions are more heavily weighted toward south Asia than they were in the 1970s and 1980s, when many of the Arctic haze studies took place. A recent analysis of long-term BC concentrations at Alert show a 55% decline since the late 1980s [Sharma et al., 2004]. This decline appears to be correlated with decreased emissions from the FSU.
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[11] Several studies, focused more on the outflow from Asia, hint at a potentially significant role for East Asian pollution in the Arctic. Wilkening et al. [2000] reported a significant level of east Asian pollution transported across the Pacific to North America and suggested that this may be an important Arctic source as well. Where there is Asian dust, there is often black carbon, as reported by Perry et al. [1999] who frequently observed black carbon mixed with dust, and sometimes independent of dust, over Hawaii in the springtime. Kaneyasu and Murayama [2000] reported very high levels of BC (>150 ng m⁻³) in the north central Pacific. The BC was associated with high levels of sulfate and not with potassium, indicative of a coal burning source rather than a biomass source. Their analysis indicated that it was derived from Asia, lofted to high altitudes, transported out over the Pacific, where it descended to the surface. A similar transport pathway was presented by Raatz [1985]. VanCuren and Cahill [2002] found substantial levels of Asian dust in decade-long records at elevated sites in North America. They argued that the dust is transported steadily, during all seasons except winter, at altitudes of 500–3000 meters. After further analysis of the data, VanCuren [2003] found the Asian dust is mixed with substantial amounts of combustion products, including elemental carbon. The export of pollutants from Asia has been the topic of recent campaigns, such as the spring 2001 ACE Asia (Aerosol Characterization Experiment) and the spring 2002 NOAA-ITCT 2K2 (Intercontinental Transport and Chemical Transformation 2002) project. During the NOAA-ITCT 2K2, rapid transport of high altitude (>2 km) Asian urban and biomass pollutants and particles across the Pacific was reported [Bertschi et al., 2004]. Matsuki et al. [2003] used aircraft, lidar and trajectory analysis, and Liang et al. [2004] used the GEOS CHEM model, to show that during winter the transport appears to be facilitated by uplift ahead of cold fronts and rapid transport by westerlies; during summer convective uplift also lofts pollution from the boundary layer. During springtime this transport occurs throughout the column primarily between 20–50°N; during summer the transport shifts to higher levels (>2–4 km) and to higher latitudes, 30–60°N. During ACE Asia, Cahill [2003] used elemental analysis and back trajectory to demonstrate the transport of Asian aerosols into Alaska and the sub-Arctic. Biscaye et al. [2000] also reported large amounts of Asian dust transported from Asia across North America, with a reduction of less than a factor of 10 as it crosses North America en route to Greenland. They postulated that Asian aerosol pollutants should have a similar fate. Indeed, significant Asian dust, along with background pollution, was observed in the Arctic during the spring of 1976 [Rahn et al., 1977].
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[12] Bowling and Shaw [1992] used thermodynamical argument to indicate that in order for polluted air to reach the Arctic via isentropic flow, low-level haze probably needs to originate from smoke stack injections into dry air; higher-level haze (above 3 km) would need to come from an extremely dry and/or high altitude source, such as a desert. This analysis might be consistent with a mixed dust-pollution source region such as the Asian Steppes. Hot dry biomass burning conditions might also satisfy the thermodynamic requirements.
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[13] We use our global model to examine the degree to which the Arctic is impacted by the more distant south Asian and low-latitude biomass regions which have the largest emissions, compared with the previously studied “Arctic haze” source regions of Europe, Russia and North America....

3.5 Deposition to Greenland...

[35] The model indicates that the largest contribution to BC deposited on Greenland is from south Asia (20–30%), with nearly as much coming from Europe. North America and northern biomass burning contribute 10–20% each. Russia contributes at least 10% over the western portion of Greenland....

4. Discussion

[39] Our global model indicates that most of the black carbon in the present-day Arctic comes from industrial and biofuel sources in south Asia and from biomass burning. Such BC arrives in the Arctic at higher altitudes throughout the year, in contrast with the surface-level springtime haze that is often the focus of Arctic haze studies. We do not imply that most of the BC in these distant regions is transported to the Arctic. On the contrary, according to our model most of south Asian BC remains south of 60°N. However enough of it makes its way north to become the major contributor to Arctic BC, so that about 20–40% of Arctic BC optical thickness comes from south Asia. This region has the largest industrial BC emission, about 21% of the global emission. It contributes about 20% to the lower troposphere winter-spring transport to the Arctic, or Arctic haze, and to surface deposition. Because the south Asian BC tends to travel at higher altitudes, it contributes a higher percentage to optical thickness and radiative forcing (20–40%)....

[40] Again, most of these [BC] biomass emissions remain at low latitudes and contribute to the BC load there. However, enough of the BC is lofted to higher altitudes, according to the model, to make significant contributions to the Arctic burden. About 60% of the global BC is from southern biomass burning. In the Arctic it contributes substantially to optical thickness and radiative forcing (10–20%).

[41] In this study we have distinguished between biomass and industrial emissions. If we had combined these, we would have found comparable contributions from south Asia and Russia, since most of the northern biomass burning emissions are from Russia. Thus, as seen in Figure 4, the total Russian contribution to the annual mean optical thickness is about 30%, similar to that from south Asia. However the northern biomass burning is maximum during summer and fall and thus generally should not contribute significantly to the springtime Arctic haze.
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[42] We have assumed the “climatological” biomass burning emissions inventory of Cooke and Wilson [1996]. We note that it does not include biomass burning from China, and is thus lacking at least 1/4 of Asian biomass (according to the year 2000 estimates of Streets et al. [2003]). Also we note that there is considerable interannual variability for Russian biomass burning [Duncan et al., 2003]. Thus the contribution of northern biomass to the Arctic should also vary, and this could cause interannual variability in Arctic BC.
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[43] Sulfur industrial emissions are distributed differently than BC, with relatively less coming from south Asia and more from Russia. The model indicates that Russia makes the greatest contribution to Arctic sulfate optical thickness (24%), followed by south Asia (17%), Europe (14%) and North America (13%). The prominent role of Russian sulfur emissions is consistent with many Arctic haze studies. However, the SO₂ from south Asia again makes a substantial contribution to Arctic aerosol pollution. Note that at the peak of Russian industrial activity, that is, 2–3 decades ago, Russian emissions would have contributed more of both sulfate and BC.
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[44] The distant sources are generally not considered in studies of pollution in the Arctic. This may be because their contribution to the surface level winter-spring Arctic haze is less than that of Europe and Russia. Transport from south Asia tends to occur at higher altitudes and for a greater portion of the year than traditionally assumed for Arctic haze. In addition, the long-distance transport from south Asia and southern biomass regions may take longer, further limiting these distant sources from trajectory analysis.
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[45] Our results are consistent with other studies that suggest a large amount of Arctic pollutants, especially black carbon, travels to the Arctic at high altitudes. Arctic aircraft observations [e.g., Hopper et al., 1994; Raatz et al., 1985] found BC to increase with altitude in many regions of the Arctic. The Northern Atlantic, which appears in our model to be downwind of the Arctic BC from south Asia (Figure 4), also appears to have increasing carbonaceous material with altitude [Novakov et al., 1997].

[46] Carbonaceous aerosols are notoriously difficult to simulate and our results consequently come with caveats. The model tends to underestimate BC concentrations near source regions and overestimate concentrations in more remote regions. This is consistent with the findings of Sato et al. [2003], who found BC absorption in 2 models to be lower by a factor of 2–4 compared to AERONET observations, which are predominantly located near source regions. The cause of the discrepancy is still not understood. Sato et al. [2003] estimated that a factor of two in excess BC absorption may be a result of internal mixing of aerosols rather than a BC mass deficiency, but this would not fully explain the observed BC absorption. Perhaps the emissions are too small and model lifetimes too long. In any case, it may be that this causes an exaggerated transport from the distant south Asia and southern biomass regions to the Arctic. The model overestimates the concentrations in the upper troposphere and lower stratosphere, again pointing to excessive contributions from south Asia and southern biomass, which dominate the burden there.
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[47] Despite the possibility that the model exaggerates long-range transport of aerosols, our results suggest that these distant source regions are probably significant contributors to Arctic BC abundance. The existence of substantial contribution from distant sources is supported by observations such as large BC amount at midlevels of the troposphere, so there is evidence supporting a prominent role for southeast Asian sources in the Arctic. The timing and location of Arctic warming and sea ice loss in the late 20th century is consistent with south Asian sources. According to Baumgardner et al. [2004], BC concentrations in the UT/LS over the Arctic seem to have doubled between 1980 and 1995 (although they also indicate that the early data are highly uncertain). BC emissions from developed countries have declined and aircraft are apparently not to blame. However, during this time BC emissions from China and India have nearly doubled [Novakov et al., 2003]. Also, the model indicates that most of the concentrations in this region of the UT/LS are from south Asia.
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[48] According to the 2002 AMAP Assessment [MacDonald et al., 2003], the past three decades show significant decreases in sea ice thickness and extent. This recent decrease is greatest in spring and fall and occurs in the western Arctic (western North America and Siberia). These observations defy recent modeling efforts, which show the largest impact of increased CO₂ on the Arctic winter rather than summer. [MacDonald et al., 2003]. The pattern of sea ice loss is believed to be linked to the phase of the AO [MacDonald et al., 2003]. However it is interesting that these decades correspond to the increases in BC from south Asia, and that this BC is transported over the Pacific and into the western Arctic, during summer as well as spring. Prior to this, sea ice also decreased during the 1930s–1940s. However this occurred during winter in the eastern part of the Arctic. Again it is interesting to note that during this earlier period, pollution from coal burning in the United States, Europe and Russia [Novakov et al., 2003] would have been transported to the Arctic during winter-spring, and the Eurasian sources would deposit heavily in the eastern Arctic (see Figure 10).

[49] Although our model has considerable uncertainties, we feel the results, together with other lines of evidence, warrant a careful look at the potential impact of south Asia and low-latitude biomass sources on Arctic BC. Studies which associate elements found in the Arctic with various pollution sources should consider these distant sources. For example, mercury has been observed to increase in the Arctic and this may be traced to coal burning in Asia [Macdonald et al., 2003]. Trace element studies of emissions from south Asia, along with Europe and Russia should be compared with those in Arctic pollution. Ideally such analysis would be done using aircraft observations, since much of the Arctic BC may never reach the surface but may remain at higher altitudes."...


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Note as of 2/3/15: Below is same study as above but posted a long time ago and links are now dead. I posted additional portions above after finding an active link.

Between 1980 and 1995, "BC (black carbon) emissions from developed countries have declined and aircraft are apparently not to blame. However, during this time BC emissions from China and India have nearly doubled."

2/25/2005, "Distant origins of Arctic black carbon: A Goddard Institute for Space Studies ModelE experiment," Dorothy Koch and James Hansen, NASA Goddard Institute for Space Studies, Journal of Geophysical Research
p.1 "Black carbon (BC) particles, derived from incomplete combustion of fossil fuels and biomass, may have a severe impact on the sensitive Arctic climate, possibly altering the temperature profile, cloud temperature and amount, the seasonal cycle, and the tropopause level and accelerating polar ice melting. We use the Goddard Institute for Space Studies general circulation model to investigate the origins of Arctic BC by isolating various source regions and types. The model suggests that the predominant sources of Arctic soot today are from south Asia (industrial and biofuel emissions) and from biomass burning.

These are the primary global sources of BC (approximately 20% and 55%, respectively, of the global emissions), and BC aerosols in these regions are readily lofted to high altitudes where they may be transported poleward. According to the model the Arctic BC optical thickness is mostly from south Asia (30%) and from biomass (28%) (with slightly more than half of biomass coming from north of 40 N); North America, Russia, and Europe each contribute 10–15%. Russia, Europe, and south Asia each contribute about 20–25% of BC to the low-altitude springtime ‘‘Arctic haze.’’ In the Arctic upper troposphere/lower stratosphere during the springtime, south Asia (30–50%) and low-latitude biomass (20–30%) are dominant, with a significant aircraft contribution (10–20%).

Industrial S emissions are estimated to be weighted relatively more toward Russia and less toward south Asia (compared with BC). As a result, Russia contributes the most to Arctic sulfate optical thickness (24%); however, the south Asian contribution is also substantial (17%). Uncertainties derive from source estimates, model vertical mixing, and aerosol removal processes. Nevertheless, our results suggest that distant sources contribute more to Arctic pollution than is generally assumed."...

page 12, "[47] Despite the possibility that the model exaggerates
long-range transport of aerosols, our results suggest that
these distant source regions are probably significant contributors
to Arctic BC abundance. The existence of substantial
contribution from distant sources is supported by
observations such as large BC amount at midlevels of the
troposphere, so there is evidence supporting a prominent
role for southeast Asian sources in the Arctic. The timing
and location of Arctic warming and sea ice loss in the late
20th century is consistent with south Asian sources.
According to Baumgardner et al. [2004], BC concentrations
in the UT/LS over the Arctic seem to have doubled between
1980 and 1995 (although they also indicate that the early
data are highly uncertain). BC emissions from developed
countries have declined and aircraft are apparently not to
blame. However, during this time BC emissions from China
and India have nearly doubled [Novakov et al., 2003]. Also,
the model indicates that most of the concentrations in this
region of the UT/LS are from south Asia....

[48] According to the 2002 AMAP Assessment
[MacDonald et al., 2003], the past three decades show
significant decreases in sea ice thickness and extent....
However it is interesting that these decades correspond to the increases in BC from south Asia, and that this BC is transported over the Pacific and into the western Arctic, during summer as
well as spring. Prior to this, sea ice also decreased during
the 1930s–1940s. However this occurred during winter in
the eastern part of the Arctic. Again it is interesting to note
that during this earlier period, pollution from coal burning
in the United States, Europe and Russia [Novakov et al.,
2003] would have been transported to the Arctic during
winter-spring, and the Eurasian sources would deposit
heavily in the eastern Arctic (see Figure 10).
[49] Although our model has considerable uncertainties,
we feel the results, together with other lines of evidence,
warrant a careful look at the potential impact of south Asia
and low-latitude biomass sources on Arctic BC. Studies
which associate elements found in the Arctic with various
pollution sources should consider these distant sources. For
example, mercury has been observed to increase in the
Arctic and this may be traced to coal burning in Asia
[Macdonald et al., 2003]. Trace element studies of emissions
from south Asia, along with Europe and Russia should
be compared with those in Arctic pollution. Ideally such
analysis would be done using aircraft observations, since
much of the Arctic BC may never reach the surface but may remain at higher altitudes."...


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