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A brighter future for the Arctic

A brighter future for the Arctic

This is a follow-up from a previous publication. Recently, a new analysis of the impact of Black Carbon in the Arctic was conducted within a European Union Action.

“Difficulty in evaluating, or even discerning, a particular landscape is related to the distance a culture has traveled from its own ancestral landscape. As temperate-zone people, we have long been ill-disposed toward deserts and expanses of tundra and ice. They have been wastelands for us; historically we have not cared at all what happened in them or to them. I am inclined to think, however, that this landscape is able to expose in startling ways the complacency of our thoughts about land in general. Its unfamiliar rhythms point up the narrow impetuosity of Western schedules, by simply changing the basis of the length of the day. And the periodically frozen Arctic Ocean is at present an insurmountable impediment to timely shipping. This land, for some, is irritatingly and uncharacteristically uncooperative.”

            -Barry Lopez, Arctic Dreams, 1986


Study

Back in the 1980s the Arctic was a different place. It is one of the fastest changing regions of our planet and since then, Arctic sea ice volume has more than halved (Figure 1). Our study took place in the 2010s, when the Arctic moved into a new regime and sea ice volume showed unprecedented lows. In the last 3 years since our study ended this decline has just continued.

Figure 1: Satellite era (1979-2018) Arctic ice data. LEFT: Arctic sea ice volume, in 1000 km3 RIGHT: Normalized arctic sea ice extent. (Credit: Zachary Labe, Department of Earth System Science, The University of California, Irvine @ZLabe)

During 4 years, we collected small airborne particles at 5 different sites around the Arctic; 1 to 2 years per site. Later, we measured  the concentrations and isotopic sources of black carbon (BC) aerosols, a product of incomplete combustion of biomass and fossil fuels, and a subfraction of the total collected aerosol.

All living organisms have more or less the same relative amount of radiocarbon atoms. We call it a similar ‘isotopic fingerprint’. Through photosynthesis plants take up CO2. About 1 in 1012 CO2 molecules contains the naturally occurring (but unstable) radiocarbon atom (14C), which is formed high up in the atmosphere through solar radiation. Black carbon from biomass burning thereby has a contemporary radiocarbon fingerprint. When plants die, the radiocarbon atoms are left to decay, and no new radiocarbon is being built into the plant. Radiocarbon’s half-life is 5730 years, which means that fossils and consequentially soot from fossil fuels is completely depleted of radiocarbon.

For the same periods and sites of our observations (see Figure 2), we also simulated black carbon concentration and sources.

Figure 2: Observational sites of our study. Clockwise from top: Utqiaġvik (formerly known as Barrow, Alaska), Tiksi Observatory (Siberia), Zeppelin Observatory (Svalbard), Abisko (Sweden), and Alert (Canada).

This was done with an atmospheric transport model (FLEXPART), using emission inventory data for fossil and biofuels (ECLIPSE), and biomass burning (GFED) (see Figure 3). Emission inventories like ECLIPSE calculate emissions of air pollutants and greenhouse gases in a consistent framework. They rely on international and national statistics of the  amount of consumed energy sources for e.g., energy use, industrial production, and agricultural activities. GFED uses MODIS satellite measurements of daily burnt area. This is used – together with ’emission factors’ (i.e. amount of emitted species per consumed energy source unit) – to calculated emissions of several different gas and particle species. The details and methodologies have also been described in a previous EGU ASxCR blogpost.

Figure 3: Model setup used in our study. Anthropogenic emissions of BC are from IIASA’s ECLIPSE emission inventory and biomass burning (wild fire and agricultural fires) are from the Global Fire Emission Database (GFED). The atmospheric transport model itself is FLEXPART, developed by NILU in Norway.

Black carbon, a short live climate pollutant (SLCP), is the second or more likely third largest warming agent in the atmosphere after the greenhouse gases carbon dioxide and methane. Unlike the two gases, it is less clear how big the net warming effect of BC is. There are several open questions, that lead to the current uncertainty: 1. How much BC is exactly put into the atmosphere? 2. How long does it stay in the air and where is it located? 3. Where from and where to is it transported, and where and when is it deposited? 4. How does it affect the earths radiative balance by darkening snow and ice, and most importantly of all: how does it interact with clouds. We have a fair understanding of all these processes, but still, relatively large uncertainties remain to be resolved. Depending on how much BC is in the air and where it is located in the atmosphere, it can have different effects (e.g., strong warming, warming, or even cooling). And all these things need to be measured, and simulated correctly by computer models.

Current multi-model best estimates by the Arctic Monitoring and Assessment Programme say that BC leads to increases of Arctic surface temperature of 0.6°C (0.4°C from BC in the atmosphere and 0.2°C from BC in snow) based on their radiative forcing (see Figure 4).

Figure 3: Radiative forcing for all greenhouse gases (GHG), carbon dioxide (CO2), methane (CH4), and black carbon (BC). All numbers are for global estimates, except the last bar to the right, which is for the Arctic only. Data according to the IPCC 5th Assessment Report (2013), an extensive review on black carbon (Bond et al. 2013), and best estimates by the Arctic Monitoring Assessment Programme (AMAP 2015). Range of uncertainties (if available) are shown as white vertical line.

It is important however to note, that our main focus on emission reduction should target (fossil-fuel) CO2 emissions, because they will affect the climate long after (several centuries) they have been emitted. And reduction in these sources means reduction in soot as well, since soot is also a combustion product. Reduction that targets soot specifically can be achieved by installation of particulate filters (retrofitting of old engines and stringent standard for new vehicles), shifting to cleaner fuels, burning techniques, or introduction and enforcement of inspection and maintenance programs to assure compliance with already existing legislation.

It is recognized internationally that for effective implementation of the Paris Agreement (mitigation effort to hold the average global temperature well below 2°C relative to the preindustrial levels), mitigation measures of short live climate pollutants (such as BC and methane) need to be considered. As the Arctic environment is more sensitive to climate change, knowing exactly which origins (source types and regions) are contributing to black carbon in this part of the world is important for effective mitigation measures.

Source attributions of black carbon depend on the altitude where the aerosol is located at the time of measurement or modelling. Wildfires are known to contribute more at higher elevations during the fire seasons (Paris et al., 2009) than at the Arctic surface. Several of the global chemical models have already approximately predicted the proportion of source influence but their accuracy depends on the emissions input and performance of the model. Part of this problem is, that these models get input from emission inventories. These inventories tell the model where, when and how much black carbon is emitted, kind of like instructions from a cookbook.

But the different cook books don’t agree on the amount of black carbon that goes into our annual black carbon cake. Additionally, all the different cookbooks have different recipes for different years. If we take a best estimate of global black carbon emissions, our annual cake  has about the size (and weight; because of similar densities of limestone/granite and soot) of the great pyramid of Giza (7500 gigagrams). But the range of estimates vary immensely (2000-29000 gigagrams) (see Figure 5). And these numbers are only for man-made emissions (fossil fuels and biofuels) i.e. excluding wildfires and natural biomass burning. A recent multi-model analysis puts global annual BC fire emissions between 1000 and 6000 gigagrams. To correct these models and the emission inventories we rely on observational data to validate the model results.

Figure 5: Uncertainty in global annual BC emissions ranges from 2000 to 29000 Gg (according to Bond et al. 2013

The model set-up we used did really well in simulating soot concentrations. A bit less well in simulating fuel types (sources) – better for fossil fuels than biofuels and biomass burning. The model simulated that 90% of BC emissions (by mass) – reaching surface level – in the Arctic originated form countries north of 42°N.

In our isotope measurements, we found that black carbon sources had a strong seasonality, with high contributions of fossil fuels to black carbon in the winter (75%) and moderate (60%) in the summer. Black carbon concentrations where roughly four times higher in winter than in summer. Concentrations of black carbon at the different stations were also relatively different from each other. These surface level (<500m above sea level) Pan-Arctic results, based on our 14C method, were not very surprising. Few individual locations, as used in our latest study, have previously been published and had similar sources(e.g., Barrett et al., 2015. Winiger, et al, 2015, 2016). However, the sources in our study were relatively uniform for all stations and almost in seasonal sync with each other (high fossil winter, low fossil summer). This could have important implications for policy related questions.

Uniform sources could mean that mitigation measures could have a stronger impact, if the right sources are tackled at the right time, to keep the Arctic from becoming a small ice floe, not large enough to stand on. There could be brighter days ahead of us.

Edited by Dasaraden Mauree


Patrik Winiger is Research Manager at the ETH Zürich and guest researcher at the Department of Earth Sciences, Vrije Universiteit Amsterdam. His research interest focuses on sources and impact of natural and anthropogenic Short Lived Climate Pollutants and Greenhouse Gases. He tweets as @PatrikWiniger.

 

 

The perfect ice floe

The perfect ice floe

Current position: 89°31.85 N, 62°0.45 E, drifting with a multi-year ice floe (24th August 2018)

With a little more than three weeks into the Arctic Ocean 2018 Expedition, the team has found the right ice floe and settled down to routine operations.

Finding the perfect ice floe for an interdisciplinary science cruise is not an easy task. The Arctic Ocean 2018 Expedition aims to understand the linkages between the sea, microbial life, the chemical composition of the lower atmosphere and clouds (see previous blog entry) in the high Arctic. This means that the “perfect floe” needs to serve a multitude of scientific activities that involve sampling from open water, drilling ice cores, setting up a meteorological tower, installing balloons, driving a remotely operated vehicle, measuring fluxes from open leads and sampling air uncontaminated from the expedition activities. The floe hence needs to be composed of multi-year ice, be thick enough to carry all installations but not too thick to allow for drilling through it. There should also be an open lead large enough for floating platforms and the shape of the floe needs to be such that the icebreaker can be moored against it on the port or starboard side facing all for cardinal directions depending on where the wind is coming from.

The search for the ice floe actually turned out to be more challenging than expected. The tricky task was not only to find a floe that would satisfy all scientific needs, but getting to it north of 89°N proved exceptionally difficult this year. After passing the marginal ice zone north of Svalbard, see blue line on the track (Figure 2), progress through the first year ice was relatively easy. Advancing with roughly 6 knots, that is about 12 km/h, we advanced quickly. After a couple of days however, the ice became unexpectedly thick with up to three meters. This made progress difficult and slow, even for Oden with her 24,500 horse powers. In such conditions the strategy is to send a helicopter ahead to scout for a convenient route through cracks and thinner ice. However, persistent fog kept the pilot from taking off which meant for the expedition to sit and wait in the same spot. For us aerosol scientists looking at aerosol-cloud interactions this was a welcome occasion to get hand on the first exciting data. In the meantime, strong winds from the east pushed the pack ice together even harder, producing ridges that are hard to overcome with the ship. But with a bit of patience and improved weather conditions, we progressed northwards keeping our eyes open for the floe.

Figure 2: Cruise track with drift. The light red line indicates the track to the ice floe, the dark red line indicates the drift with the floe. The thin blue line is the marginal ice zone from the beginning of August.

As it happened, we met unsurmountable ice conditions at 89°54’ N, 38°32’ E, just about 12 km from the North Pole – reason enough to celebrate the farthest North.

Figure 3: Expedition picture at the North Pole. (Credit: SPRS)

Going back South from there it just took a bit more than a day with helicopter flights and good visibility until we finally found ice conditions featuring multiple floes.

And here we are. After a week of intense mobilization on the floe, the four sites on the ice and the instrumentation on the ship are now in full operation and routine, if you stretch the meaning of the term a bit, has taken over. A normal day looks approximately like this:

7:45:  breakfast, meteorological briefing, information about plan of the day; 8:30 – 9:00: heavy lifting of material from the ship to the ice floe with the crane; 9:00 (or later): weather permitting, teams go to the their sites, CTDs are casted from the ship if the aft is not covered by ice; 11:45: lunch for all on board and pick-nick on the floe; 17:30: end of day activities on the ice, lifting of the gangway to prevent polar bear visits on the ship; 17:45: dinner; evening: science meetings, data crunching, lab work or recreation.

Figure 4: Sites on the floe, nearby the ship. (Credit: Mario Hoppmann)

At the balloon site, about 200 m from the ship, one balloon and one heli-kite are lifted alternately to take profiles of radiation, basic meteorological variables and aerosol concentrations. Other instruments are lifted up to sit over hours in and above clouds to sample cloud water and ice nucleating particles, respectively. At the met alley, a 15 m tall mast carries radiation and flux instrumentation to characterize heat fluxes in the boundary layer. The red tent at the remotely operated vehicle (ROV) site houses a pool through which the ROV dives under the flow to measure physical properties of the water. The longest walk, about 20 minutes, is to the open lead site, where a catamaran takes sea surface micro layer samples, a floating platform observes aerosol production and cameras image underwater bubbles. The ice core drilling team visits different sites on the floe to take samples for microbial and halogen analyses.

Open Lead site. (Credit: Julia Schmale)

Importantly, all activities on the ice need to be accompanied by bear guards. Everybody carries a radio and needs to report when they go off the ship and come back. If the visibility decreases, all need to come in for safety reasons. Lab work and continuous measurements on the ship happen throughout the day and night. More details on the ship-based aerosol laboratory follow in the next contribution.

Edited by Dasaraden Mauree


Julia Schmale is an atmospheric scientist at the Paul Scherrer Institute in Switzerland. Her research focuses on aerosol-cloud interactions in extreme environments. She is a member of the Atmosphere Working Group of the International Arctic Science Committee and a member of the Arctic Monitoring and Assessment Programme Expert Group on Short-lived Climate Forcers .

Into the mist of studying the mystery of Arctic low level clouds

Into the mist of studying the mystery of Arctic low level clouds

This post is the first of a “live-series of blog post” that will be written by Julia Schmale while she is participating in the Arctic Ocean 2018 expedition.

Low level Arctic clouds are still a mystery to the atmospheric science community. To understand their role the present and future Arctic climate, the Arctic Ocean 2018 Expedition is currently under way with an international group of scientists to study the ocean, lower atmosphere, clouds and aerosols.

Low level clouds in the high Arctic influence the energy budget of the region and they hence play an important role for the Arctic climate. The Arctic is warming about twice as fast as the global average, a phenomenon called Arctic amplification. The role of clouds for climate is linked to their interaction with solar radiation. They reflect short-wave radiation, thereby sending energy back to space and cooling the surface. In the case of longwave radiation, clouds reflect it back to the surface which causes a greenhouse effect that is warming the surface. The top of the clouds cools during this process, which makes air parcels surrounding the top cool as well and sink to the surface. These air masses are replaced by warmer surface air which rises. This can cause a well-mixed Arctic boundary layer. Most of the time, however, the cloud level is decoupled from the surface due to temperature inversions. This is possible when clouds are thin. In this case, clouds cannot feed on the water vapor from the surface and they might dissipate. Interaction of clouds with short-wave radiation in the summer is most of the time less important than their interaction with long-wave radiation. This is because the cloud albedo is similar to the sea ice albedo. Hence clouds do not have a strong cooling effect. However, as summer sea ice retreats and the surface gets darker, clouds may contribute to surface cooling in the future.

The overall radiative properties of clouds are further influenced by the phase of the clouds. Arctic summer clouds are normally mixed-phased, that is liquid droplets co-exist with ice crystals. Usually, ice and liquid water do not co-exist, because the ice crystals grow at the expense of liquid droplets that evaporate (because the saturation water vapor pressure is higher of liquid droplets than ice crystals). However, in simple words, in the summertime Arctic, when mixing of air masses occurs, liquid droplets form in rising air parcels that sustain the liquid layer at the bottom of the cloud which in turn feeds the ice crystal growth.

As cloud droplets and ice crystals only form on cloud condensation nuclei (CCN) and ice nucleating particles (INP), the whole complexity described above, depends on the presence of aerosol particles. But the central Arctic Ocean has an extremely limited supply of CCN and INP. Potential sources include locally produced or long-range transported particles. Long-range transport of particles – or precursor gases that form particles – to the high Arctic in the free troposphere can contribute to the number of CCN and INP. However, in the summer Arctic atmosphere precipitation is frequent and particles can be washed out along their way north. Regional transport of trace gases such as dimethyl sulfide (DMS), which is emitted from phytoplankton blooms in the marginal ice zone, can contribute to the CCN after atmospheric oxidation. Local sources in the high Arctic are however, extremely limited. Open leads, those are areas of open water which form as the sea ice is moving, can produce particles through bubble bursting. These bursting bubbles expel material such as sea salt and organic particles contained in the surface water into the air from where they might be transported to the cloud level. Another conceivable source of particles is new particle formation. This means that particles are freshly formed purely from gases. This process and the chemical nature and sources of the gases are however poorly understood.

To shed light on how cloud formation works in the summer time high Arctic and how this might change in the future with changing climatic conditions the Arctic Ocean 2018 Expedition is designed to investigate physical, chemical and biological processes from the water column to the free troposphere. The graphic below provides a schematic of the planned activities.

Arctic ocean setup by Paul Zieger

 

On 1 August, we left Longyearbyen. After a 24 hour station in the marginal ice zone, we are now heading towards the North Pole area where we look for a stable multi-year ice floe against which the ship will be moored for several weeks to drift along. This strategy will give us the opportunity for detailed process studies. In the upcoming blog contributions, several of these process studies will be featured.

Further links:
Expedition website:
https://polarforskningsportalen.se/en/arctic/expeditions/arctic-ocean-2018
Arctic ocean blog of the Paul Scherrer Institute:
https://www.psi.ch/lac/arctic-ocean-blog
Stockholm University Expedition Webpage:
https://www.aces.su.se/research/projects/microbiology-ocean-cloud-coupling-in-the-high-arctic-moccha/

Edited by Dasaraden Mauree


Julia Schmale is an atmospheric scientist at the Paul Scherrer Institute in Switzerland. Her research focuses on aerosol-cloud interactions in extreme environments. She is a member of the Atmosphere Working Group of the International Arctic Science Committee and a member of the Arctic Monitoring and Assessment Programme Expert Group on Short-lived Climate Forcers .

Black Carbon: the dark side of warming in the Arctic

Black Carbon: the dark side of warming in the Arctic

When it comes to global warming, greenhouse gases – and more specifically CO2 – are the most often pointed out. Fewer people know however that tiny atmospheric particles called ‘black carbon’ also contribute to the current warming. This post presents a paper my colleague and I recently published in Nature Communications . Our study sheds more light into the chemical make-up of black carbon, passing through the Arctic.


Black Carbon warms the climate

 Figure 1: Global radiative forcing of CO2 (green) compared to black carbon (blue). The colored bars show the mean change in radiative forcing due to the concentration of CO2 and BC in the atmosphere. The estimated range for the expected radiative forcing is everything between the white lines, which show the 90% confidence interval. (Data according to Boucher et al. 2013 (IPCC 5th AR) and Bond et al. 2013). [Credit: Patrik Winiger]

Figure 1: Global radiative forcing of CO2 (green) compared to black carbon (blue). The colored bars show the mean change in radiative forcing due to the concentration of CO2 and BC in the atmosphere. The estimated range for the expected radiative forcing is everything between the white lines, which show the 90% confidence interval. (Data according to Boucher et al. 2013 (IPCC 5th AR) and Bond et al. 2013). [Credit: Patrik Winiger]

Black Carbon (BC) originates from incomplete combustion caused by either natural (e.g., wild fires) or human (e.g., diesel car emissions) activities. As the name suggests, BC is a dark particle which absorbs sunlight very efficiently. In scientific terms we call this a strong positive radiative forcing, which means that the presence of BC in the atmosphere is helping to heat the planet. Some estimates put its radiative forcing in second place, only after CO2 (Figure 1). The significant thing about BC is that it has a short atmospheric lifetime (days to weeks), meaning we could quickly avoid some climate warming by getting rid of its emissions. Currently global emissions are increasing year by year and on snow and ice, the dark particles have a longer lasting effect due to the freeze and thaw cycle, where BC can re-surface, before it is washed away. It is important however to note, that our main focus on emission reduction should target (fossil-fuel) CO2 emissions, because they will affect the climate long after (several centuries) they have been emitted.

Arctic amplification: strongest warming in the North Pole

The Arctic is warming faster than the rest of our planet. Back in 1896, the Swede Arrhenius, (better known for his works: in chemistry), calculated, that a change in atmospheric CO2 – which at that time was a good 100 ppm lower than today – would change the temperature at higher latitudes (towards the poles) more than at lower latitudes.

Figure 2: Observation based global surface temperature anomalies for Jan-Mar (2016) in °C with respect to a 1961-1990 base year. Credit: GISTEMP Team, 2016: GISS Surface Temperature Analysis (GISTEMP). NASA Goddard Institute for Space Studies. Dataset accessed 2016-10-15 at http://data.giss.nasa.gov/gistemp/ [Hansen et al., 2010].

Figure 2: Surface temperature anomalies (in °C) for Jan-Mar (2016) with respect to a 1961-1990 baseline. [ Credit: NASA — GISTEMP (accessed 2016-10-15) and Hansen et al., 2010].

The problem with his calculations – as accurate and impressive they might have been – was, that he ignored the earth’s geography and seemed unaware of the big heat capacity of the oceans. On the southern half of our planet there is a lot more water, which can take up more heat, as compared to the northern half with more land surface. Thus, in reality the latitudes on the southern hemisphere have not heated as much as their northern counterparts and this effect came to be known as Arctic amplification.

Dark particles on bright snow and ice

Figure 3: Welcome to the Greenland Ice Sheet everybody. Probably an extreme case of ice covered in cryoconite, captured in August 2014 [Credit: Jason Box, (LINK: http://darksnow.org/)].

Figure 3: Ice covered in cryoconite, Greenland Ice Sheet, in August 2014 [Credit: Jason Box — Dark Snow project].

Greenhouse gases and BC are not the only reasons for the increase in temperature change and earlier onset of the melting season in the Arctic. Besides BC, there are other ‘light absorbing impurities’ such as dust, microorganisms, or a mixture of all of the above, better known as cryoconite. They all absorb solar radiation and thus decrease the albedo – the amount of solar energy reflected back to space – of the underlying white surface. This starts a vicious cycle by which these impurities melt the snow or ice and eventually uncover the usually much darker surface (e.g., rock or open sea water), leading to more solar absorption and the cycle continues. The effect and composition of these impurities are currently intensively studied on the Greenland ice sheet (check out the Black and Bloom, as well as the Dark Snow projects).

Black Carbon effect on climate is highly uncertain

One of the reasons for the high uncertainty of BC’s climate effects is the big range in effects it has (see white line on Figure 1), when it interacts with snow and ice (or clouds and the atmosphere).

Another source of uncertainty is probably the big estimated range in the global, and especially in the regional emissions of BC in the Arctic. For example, the emission inventory we work with (ECLIPSE), is based on international and national statistics that indicate how much of a certain fuel (diesel, coal, gas, wood, etc.) is used, and in which way it is used (vehicle sizes, machine type and age, operating conditions, etc.). These numbers can vary a lot. If we, for example, line up different emission inventories of man-made emissions (Figure 4), by comparing the two different fractions of BC (fossil fuels vs. biomass burning) at different latitudes, then we see that the closer we get to the North pole, the more these emission inventories disagree. And this is still ignoring atmospheric transport or emissions of natural sources, such as wildfires.

Computer models, necessary to calculate global climate change, are partly based on input from these emission inventories. Models used for the calculation of the transport of these tiny particles have vastly improved in recent years, but still struggle at accurately mimicking the seasonality or extent of the observed BC concentrations. To some extent this is also due to the range of parametrization in the model, mainly the lifetime of BC, including its removal from the atmosphere by wet scavenging (e.g., rain). So to better understand black carbon effects on climate, more model calculations are necessary, for which the emission inventory estimates need to be verified by observations.

Figure 4: Fraction biomass burning of BC (fbb) at different latitudes North, estimated by three different emission inventories. The green line shows the GAINS emission inventory, which was the precursor to the ECLIPSE inventory (Klimont et al. 2016) [Credit: Patrik Winiger]

Figure 4: Fraction biomass burning of BC (fbb) at different latitudes North, from three different emission inventories. The green line shows the GAINS emission inventory, which was the precursor to the ECLIPSE inventory (Klimont et al. 2016) [Credit: Patrik Winiger]

How do we trace the origin of black carbon?

This is where the science of my colleagues and me comes in. By looking at BC’s isotopic ratio of stable-carbon (12C/13C) and its radiocarbon (14C) content we were able to deduce information about the combustion sources (Figure 5).

Plants (trees) take up contemporary radiocarbon, naturally present in the atmosphere, by photosynthesis of atmospheric CO2. All living organisms have thus more or less the same relative amount of radiocarbon atoms, we talk of a similar isotopic fingerprint. BC from biomass (wood) burning thereby has a contemporary radiocarbon fingerprint.

When they die, organisms stop incorporating contemporary carbon and the radiocarbon atoms are left to decay. Radiocarbon atoms have a relative short (at least on geological time-scales) half-life of 5730 years, which means that fossils and consequentially BC from fossil fuels are completely depleted of radiocarbon. This is how the measured radiocarbon content of a BC sample gives us information on the relative contributions of fossil fuels vs. biomass burning.

The stable carbon isotopic ratio gives information on the type of combustion sources (liquid fossil fuels, coal, gas flaring or biomass burning). Depending on how a certain material is formed (e.g., geological formation of coal), it has a specific isotopic ratio (of 12C/13C), like a fingerprint. Sometimes isotopic fingerprints can be altered during transport (because of chemical reactions or physical processes like condensation and evaporation). However, BC particles are very resistant to reactions and change only very little. Hence, we expect to see the same fingerprints at the observation site and at the source, only that the isotopic signal at the observation site will be a mixture of different source fingerprints.

Figure 5/ Carbon isotopic signatures of different BC sources, summarized by E.N. Kirillova (2013).

Figure 5: Carbon isotopic signatures of different BC sources, summarized by E.N. Kirillova (2013). To give information about the isotopic fingerprint, the delta-notation is used (small delta for 12C/13C, and big delta for 12C/14C). The isotopic values show how much a certain sample is different, on a per mil scale, from an international agreed isotopic standard value (or ratio) for carbon isotopes. [Credit: fig 1 from Kirillova (2013)]

Where does the black carbon in European Arctic come from?

In our study (Winiger et al, 2016), we observed the concentrations and isotopic sources of tiny particles in airborne BC for over a year, in the European Arctic (Abisko, Sweden), and eventually compared these observations to model results, using the freely available atmospheric transport model FLEXPART and emission inventories for natural and man-made BC emissions.

Seeing our results we were first of all surprised at how well the model agreed with our observations. We saw a clear seasonality of the BC concentrations, like it has been reported in the literature before, and the model was able to reproduce this. Elevated concentrations were found in the winter, which is sometimes referred to as Arctic haze. The combustion sources showed a strong seasonality as well. The radiocarbon data showed, that fossil fuel combustion dominated in the winter and (wood) biomass burning during the low BC-burden periods in the summer. With a combination of the stable isotope fingerprints and Bayesian statistics we further concluded, that the major fossil fuel emissions came from liquid fossil fuels (most likely diesel). The model predicted a vast majority of all these BC emissions to be of European origin. Hence, we concluded, that the European emissions in the model had to be well constrained and the model parametrization of BC lifetime and wet-scavenging had to be fairly accurate for the observed region and period. Our hope is now that our work will be implemented in future models of BC effects and taken into account for future BC mitigation scenarios.

Figure 6: This is an example from the model calculations, showing where the (man-made) BC came from in January 2012. Abisko's position is marked as a blue star. The darker (red) spots show sources of higher BC contribution. This winter example was among the three highest observed (in terms of BC concentration) and the sources were ~50% wood burning, ~20% liquid fossil fuels (diesel) and ~30% coal. Some of the darkest spots can clearly be attributed to European cities.

Figure 6: Example from the model calculations, showing where the (man-made) BC came from in January 2012. Abisko’s position is marked as a blue star. The darker (red) spots show sources of higher BC contribution. This winter example was among the three highest observed (in terms of BC concentration) and the sources were ~50% wood burning, ~20% liquid fossil fuels (diesel) and ~30% coal. Some of the darkest spots can clearly be attributed to European cities. [Credit: fig4b from Winiger et al (2016)]

References

  • Anderson, T. R., E. Hawkins, and P. D. Jones (2016), CO2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today’s Earth System Models, Endeavour, in press, doi:10.1016/j.endeavour.2016.07.002.
  • Arrhenius, S. (1896), On the influence of carbonic acid in the air upon the temperature of the ground., Philos. Mag. J. Sci., 41(August), 239–276, doi:10.1080/14786449608620846.
  • Hansen, J., R. Ruedy, M. Sato, and K. Lo (2010), Global surface temperature change, Rev. Geophys., 48(4), RG4004, doi:10.1029/2010RG000345.
  • Klimont, Z., Kupiainen, K., Heyes, C., Purohit, P., Cofala, J., Rafaj, P., Borken-Kleefeld, J., and Schöpp, W.: Global anthropogenic emissions of particulate matter including black carbon, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-880, in review, 2016.
  • Kirillova, Elena N. “Dual isotope (13C-14C) Studies of Water-Soluble Organic Carbon (WSOC) Aerosols in South and East Asia.” (2013). ISBN 978-91-7447-696-5 pp. 1-37
  • Winiger, P., Andersson, A., Eckhardt, S., Stohl, A., & Gustafsson, Ö. (2016). The sources of atmospheric black carbon at a European gateway to the Arctic. Nature Communications, 7.

Edited by Sophie Berger, Dasaraden Mauree and Emma Smith
This is joint post with the Cryospheric Division , given the interdisciplinarity of the topic featured.


portraitPatrik Winiger is a PhD student at the Department of Environmental Science and Analytical Chemistry and the Bolin Centre for Climate Research, at Stockholm University. His research interest focuses on impact and mitigation of Short Lived Climate Pollutants and anthropogenic CO2 emissions. Currently he investigates the sources of black carbon aerosols in the Arctic. He tweets as @PatrikWiniger