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As we examine the world after the Paris Agreement, lessons from recent environmental trends and modelling of the impacts on the Arctic cryosphere under different greenhouse gas (GHG) concentration show, with increasing confidence, that stabilizing global temperatures near 2° C will slow but not halt large changes in the Arctic in the foreseeable future (decades). Substantial changes in the Arctic environment and feedbacks into the global system are inevitable before mid-century, even under the most optimistic greenhouse gas reduction scenarios, and are emission dependent in the second half of the century. Sea ice has undergone a regime shift from multi-year to first-year sea ice, and summer sea ice is very likely to be esentially gone within the next few decades. The Arctic cryosphere has the potential to affect ecosystems and humans outside the Arctic through sea level rise, a growing evidence of influence on weather, GHG release, and climate feedbacks to ocean and atmospheric circulation. Recent extreme winter temperatures in 2016 and lack of winter sea ice cover in winter 2017, both suggest new and rapid shifts in the Arctic. There is evidence for two-way interactions between the Arctic and midlatitudes. Although thermodynamic forcing of weather systems by rising Arctic temperatures and loss of sea ice is increasing, dynamic linkages are confounded by the large chaotic nature of the jet stream, and thus potential midlatitude impacts are nonlinear. Linkages appear to be regional (eastern Asia and eastern North America) and episodic. Extreme warming of the Arctic in winter 2016 and fall 2016 had a strong trajectories from midlatitudes.
We implemented a tagged tracer method of black carbon (BC) into a global chemistry-transport model GEOS-Chem, examined the pathways and efficiency of long-range transport from a variety of anthropogenic and biomass burning emission sources to the Arctic, and quantified the source contributions of individual emissions. Firstly, we evaluated the simulated BC by comparing it with observations at the Arctic sites and found that the simulated seasonal variations were improved by implementing an aging parameterization and reducing the wet scavenging rate by ice clouds. For tagging BC, we added BC tracers distinguished by source types (anthropogenic and biomass burning) and regions. Our simulations showed that BC emitted from Europe and Russia was transported to the Arctic mainly in the lower troposphere during winter and spring. In particular, BC transported from Russia was widely spread over the Arctic in winter and spring, leading to a dominant contribution of 62 % to the Arctic BC near the surface as the annual mean. In contrast, BC emitted from East Asia was found to be transported in the middle troposphere into the Arctic mainly over the Okhotsk Sea and East Siberia during winter and spring. We identified an important “window” area, which allowed a strong incoming of East Asian BC to the Arctic (130–180°E and 3–8 km altitude at 66°N). The model demonstrated that the contribution from East Asia to the Arctic had a maximum at about 5 km altitude due to uplifting during the long-range transport in early spring. The efficiency of BC transport from East Asia to the Arctic was smaller than that from other large source regions such as Europe, Russia and North America. However, the East Asian contribution was most important for BC in the middle troposphere (41 %) and BC burden over the Arctic (27 %).
A new PACES-coordinated modeling/measurement project focused on reducing errors in model descriptions of pollutant transport, wet removal, and chemistry at mid- and high-latitudes is being developed. This project, IMPAACT (Investigation of Multiscale Processes Affecting Atmospheric Chemical Transport) will examine the transport and evolution of aerosol and gas-phase pollutants originating in East Asia and exported to the Arctic and North America. IMPAACT will use a semi-Lagrangian approach to track these pollutants throughout lifting to the free troposphere, transport across the North Pacific, and arrival to the polar regions and the western U.S. and Canada. The role of wet removal and aqueous processes will be foci of this study, as model simulations suggest particular sensitivity of the nitrogen/ozone and aerosol budgets to these processes. IMPAACT observations will be anchored by the NASA DC-8 aircraft, which has the payload, range, and altitude capability needed for trans-Pacific measurements. Additional aircraft will operate at lower altitudes near East Asia, Alaska, western Canada, and the Northwest of the contiguous U.S. Mountaintop, surface, and shipborne observations will provide valuable information on the spatial and temporal variability of pollutant characteristics and transport. Modeling efforts will include Lagrangian, regional, global chemical transport, and chemistry-climate models, to be used for sensitivity studies, prognostic runs, and comparisons with observations. Satellite observations will be assimilated in some model runs and will provide essential data for subsequent analyses. It is anticipated that the intensive airborne portion of IMPAACT will take place in spring 2021, with flights based out of southern Japan/Okinawa, Alaska, and western North America. A U.S. scientific steering committee has written a white paper; international collaboration is solicited to further develop the science plans and execute the study.
The goal of MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) is to improve the understanding of coupled atmosphere-ice-ocean- ecosystem processes in the Central Arctic in order to support improved sea ice and regional weather forecasting as well as climate predictions. Activities within MOSAIC include ship-borne measurements on the RV Polarstern and airborne observations, e.g. with the AWI research aircraft. The latter are based on the PAMARCMIP project since 2009 and are a contribution to the DFG Transregio project Arctic Amplification – AC*3 as well as to the PACES initiative. The airborne surveys crucially contribute to fill the gap between satellite remote sensing and in situ observations. They serve as calibration and validation for satellite remote sensing. Furthermore, helicopter-based work is planned from RV Polarstern with similar instrumentation as on the research aircraft Polar 5 and Polar 6 in order to fill the temporal gap between the aircraft campaigns. Svalbard is the preferred location, but this depends on the position of the RV Polarstern. Especially for the spring activity alternates are Station Nord/Villum, Greenland (BGNO) or the Canadian Forces Station Alert, Nunavut, (CYLT). The first campaign is scheduled for spring 2020 with operation base Longyearbyen, Svalbard. The second campaign is planned for early summer 2020, during the melt season. During the airborne activity complementary measurements on board of RV Polarstern and at the central observatory are planned. It is also foreseen to deploy the German High Altitude and Long Range Research Aircraft (HALO) to extend the point measurements of RV Polarstern and the areal observations of the lower troposphere by the two AWI aircraft Polar 5 and Polar 6 to higher altitudes and over the whole Arctic area. The HALO measurements will complement the spring activity from the slower and lower flying AWI aircraft Polar 5/6.
Black carbon (BC) concentrations observed in 22 snowpits sampled in the northwest sector of theGreenland Ice Sheet in April, 2014 have allowed us to identify a strong and widespread BC aerosol deposition event, which was dated to have accumulated in the pits from two snow storms between 27 July and 2 August, 2013. This event comprises a significant portion (57% on average across all pits) of total BC deposition over 10 months (July, 2013 – April, 2014). Here we link this depositional event to forest fires burning in Canada during summer 2013 using modeling and remote sensing tools. Aerosols were detected by both the CALIOP (onboard CALIPSO) and MODIS (AQUA) instruments during transport between Canada and Greenland, confirming that this event involved emissions from forest fires in Canada. We use high resolution regional chemical transport modeling (WRF-Chem) combined with high resolution fire emissions (FINNv1.5) to study aerosol emissions, transport, and deposition during this event. The model accurately captures the timing of the deposition event and shows that the major contribution to BC deposition during the second snow storm is emissions originating from fires in Canada. However, the model under estimates BC deposition compared to measurements at all sites by a factor of 2–100. Under prediction of modeled BC deposition originates from uncertainties in fire emissions combined with uncertainties in aerosol scavenging by clouds. This study suggests that it is possible to simulate the transport of a major wildfire smoke event on regional and continental scales. Improvements in model descriptions of precipitation scavenging and emissions from wildfires are needed to correctly predict deposition, which is critical for determining the climate impacts of aerosols that originate from fires.
Historic Measurements of Arctic Air Pollution (Arctic Haze) from Barrow Observatory and the Arctic Gas and Aerosol Program (AGASP)
Air Pollution measured at the NOAA, Barrow Atmospheric Baseline Observatory (71<sup>0</sup> N, 156<sup>0</sup> W, 11 m asl) arrives predominately in easterly winds with the pollution originating in Eastern Europe and northern Russia. The pollution is highly stratified and concentrated above the Arctic marine boundary layer. As such, surface concentrations of pollution are generally much lower than those measured above the marine boundary layer (aircraft profiles). Since the early 1980’s, the concentrations of springtime pollution aerosols measured at the Barrow Observatory have been in general decline while CO<sub>2</sub> and CH<sub>4</sub> have steadily increased. Occasionally in spring, westerly winds bring dust and air pollution from Asia that has traveled over the Bering Sea into Alaska north of the Brooks Range. This air is fairly well mixed which reduces the strength of the marine boundary layer. As such, aerosol concentrations measured at the surface better represent concentrations aloft. Forest fires, especially those in Alaska and northern Canada, occasionally flow past the Barrow Observatory and may markedly reduce the solar radiation reaching the surface. Forest fire smoke flowing over the Barrow Observatory has also been measured some days later flowing past the Summit Greenland Observatory (72<sup>0</sup>N, 38<sup>0</sup>W, 3216 m asl). Numerous publications dating back to the 1970s document the history of Arctic air pollution and especially ~ 250 publications on “Arctic Haze” in dedicated issues of G.R.L (1984), 3 volumes of Jr. Atmos. Chem. (1989) and 3 volumes of Atmos. Environ.(1985, 1989 and 1993).
Air pollutants in the Arctic have impacts on climate change, ecosystems, regional air quality, and human health. Rapid changes to and complex interactions within the Arctic environment due to climate change and socio-economic drivers mean that there is an urgent requirement to improve understanding of sources of Arctic air pollutants. Previous studies have identified significant deficiencies in model skill in simulating Arctic distributions of air pollutants, both at the surface and in the vertical profile. Such deficiencies in predictive capability and a lack of observations at high latitudes present major challenges to our ability to make credible near- and long-term projections of Arctic environmental change. Improved quantification of the relative contributions of different pollutant sources in the Arctic atmosphere, and their impacts is needed to provide a sound scientific basis for sustainable solutions and adaptive strategies. Here we investigate drivers of model variability in simulating tropospheric ozone and NOy in the high latitude troposphere. We use results from multi-model inter-comparison experiments compared with a limited ensemble of single model perturbation experiments to shed light on possible drivers of inter-model variability in Arctic ozone and NOy budgets. We also discuss implications for kinetic parameter uncertainties for confidence in modelled ozone in anthropogenic and biomass burning pollution plumes, and relevance to the Arctic. Our results serve as pointers to towards processes that could be targeted in future field or lab experimental efforts to reduce uncertainty in Arctic trace gas budgets.
Model simulations of an intensive field campaign conducted over the Canadian high Arctic during the summer of 2014 were carried out using an online regional air quality model (GEM-MACH). Model results were compared with in-situ measurements from multiple platforms. The model captured the regional sources and transport to the Canadian Arctic well; the vertical structure of the lower atmosphere was well simulated by the model. The model results indicate that under transient conditions during summer, the Canadian high Arctic can be impacted by long-range transported pollutants from both anthropogenic and natural (e.g., biomass burning) sources in southern regions, including western and central Canada, as well as eastern North America. In this study, further analysis was carried out focussing on two cases during the campaign: 1) an elevated plume reaching the Arctic influenced by both biomass burning (over western Canada) and anthropogenic (over central Canada) sources, where biomass burning aerosols being scavenged during the transport is evident; and 2) transport of biomass burning plume at low altitudes over cold Arctic water channels when elevated plume may be bought down due to descending motion (over Labrador sea and Baffin Bay).
Arctic is warming rapidly in past few decades. Recent studies have suggested large increase of BVOC emissions in this region as a result of warming and vegetation greening. Here we use aircraft measurements, satellite observations of formaldehyde and formic acid, interpreted with a global chemical transport model (GEOS-Chem), to better quantify the decadal trend of BVOC emissions in this region. A large uncertainty of this work lies in the model representation of monoterpene oxidation. We use data collected during the second phase (summer) of NASA ACRTAS field campaign, along with the Master Chemical Mechanism (v3.3.1), to quantify the yield of HCHO and HCOOH from monoterpene oxidations. This knowledge will then be applied to estimate monoterpene and isoprene emissions in this region using satellite observations.
Mineral dust can have a strong radiative forcing impact in the Arctic, including its effect on snow albedo, which has seen relatively little attention compared to black carbon, despite its probably much larger importance. Global dust models focus on the main dust source regions in other parts of the world and largely ignore high-latitude dust sources. Groot Zwaaftink et al. (2016, 2017) have recently shown that local Arctic or near-Arctic dust sources dominate dust deposition in the Arctic, whereas lower-latitude sources are more important for the Arctic dust total atmospheric column loading. We review their findings and those of other recent studies, many of which focussed on Iceland. The review will discuss source areas, compare lower vs. higher latitude source regions, quantify dust deposition, radiative impacts and discuss uncertainties. Groot Zwaaftink, C. D, H. Grythe, H. Skov, and A. Stohl (2016): Substantial contribution of northern high-latitude sources to mineral dust in the Arctic. J. Geophys. Res. 121, 13678-13697, doi:10.1002/2016JD025482. Groot Zwaaftink, C. D, Ó. Arnalds, P. Dagsson-Waldhauserova, S. Eckhardt, T. Johannsson, J. M. Prospero, and A. Stohl (2017): Interannual variability of Icelandic mineral dust emission and atmospheric transport. Submitted to Atmos. Chem. Phys.
NETCARE (Network on Climate and Aerosols: Addressing Fundamental Uncertainties in Remote Canadian Environments) is a Canadian research network established four years ago. This talk will present an overview of the network, which has had research projects involving ground-, ship- and aircraft-based observations, alongside GCM and CTM modeling efforts. This talk will address in particular results from summertime observations when the open ocean becomes a more dominant element of the regional biogeochemical system. In particular, observation from the Canadian Arctic indicate that substantial new particle formation and growth occur in marine boundary layer environments, with impacts on both the number and chemical nature of particles that act as cloud condensation nuclei. Most of the growth of these particles is via condensation of organic mass. The detailed input of molecules from the oceans however, in particular with respect to the organic species that allow particles to grow to CCN sizes, is uncertain. Correlations of gas-phase semi-volatile organic molecules with the dissolved organic content of ocean water suggest the source of the organic mass is marine. The overall motivation for studies of the Arctic atmosphere in the clean summertime is to better understand the nature of biogeochemical processes that will become more prevalent as summer sea ice retreats.
We introduce long term dataset of aerosol scattering and absorption properties and combined aerosol optical properties measured in Pallas Atmosphere-Ecosystem Supersite in Northern Finland. The station is located 170 km north of the Arctic Circle. The station is affected by both pristine Arctic air masses as well as long transported air pollution from northern Europe. We studied the optical properties of aerosols and their radiative effects in continental and marine air masses, including seasonal cycles and long-term trends. The average (median) scattering coefficient, backscattering fraction, absorption coefficient and single scattering albedo at the wavelength of 550 nm were 7.9 (4.4) 1/Mm, 0.13 (0.12), 0.74 (0.35) 1/Mm and 0.92 (0.93), respectively. We observed clear seasonal cycles in these variables, the scattering coefficient having high values during summer and low in fall, and absorption coefficient having high values during winter and low in fall. We found that the high values of the absorption coefficient and low values of the single scattering albedo were related to continental air masses from lower latitudes. These aerosols can induce an additional effect on the surface albedo and melting of snow. We observed the signal of the Arctic haze in marine (northern) air masses during March and April. The haze increased the value of the absorption coefficient by almost 80% and that of the scattering coefficient by about 50% compared with the annual-average values. We also observed clear relationship with temperature and aerosol scattering coefficient and aerosol optical depth. This was related to increase of biogenic secondary organic aerosol (BSOA) as a function of temperature. The direct radiative feedback parameter associated with the formation of BSOA was estimated.
Russia’s Black Carbon Emissions: The Arctic and Beyond Pacific Northwest National Laboratory has worked on BC emission study in Russia. The study consists of three part: BC diesel emission inventory for Murmansk, Russia-wide emission inventory from diesel sources and all-Russia inventory of BC emissions from all sources. The study estimates BC emissions from diesel sources in Murmansk Region and Murmansk City, the largest city in the world above the Arctic Circle. The study presents a detailed inventory of diesel sources including on-road vehicles, off-road transport (mining, locomotives, construction and agriculture), ships and diesel generators. The study presents a detailed inventory of Russian BC emissions from diesel sources. Drawing on a complete Russian vehicle registry with detailed information about vehicle types and emission standards, the study analyzes BC emissions from diesel on-road vehicles. Using Russian activity data and fuel-based emission factors, we also present BC emissions from diesel locomotives and ships, off-road engines. The study also factors in the role of superemitters in BC emissions from diesel on-road vehicles and off-road sources. Finally, the study estimates Russia-wide BC emissions from all sources. Using a wide variety of studies, we assess Russian BC emissions from wildfires, flaring, transportation, the domestic sector, power generation, heating and industry. Using satellite data, we estimate emissions from flaring, the second largest source of BC emissions after wildfires. We also present an adjusted estimate of Arctic forcing from Russian BC emissions.
Black carbon emissions are one of the Far North’s three main short-lived climate-forcing pollutants and pose a health threat to local citizens. Black carbon emissions from Arctic States alone accounts for 30% of Arctic warming. Black carbon is emitted from a number of sources including the burning of diesel fuel, on which Northern communities are especially dependent; wild fires; agricultural and solid waste burning; and residential wood combustion. Throughout the Arctic, there are significant knowledge gaps regarding local black carbon emissions and the risks to communities. Local communities generally lack the capacity to assess black carbon emissions, public health impacts, and mitigation options. The project will: Assess, on a pilot basis, local sources of black carbon emissions from Arctic Alaskan and Russian villages, and possibly a Saami community Provide a broad characterization of associated risks to public health Explore short and long-term mitigation options Assess and, where possible, strengthen local capacities to identify, mitigate, and prevent black carbon pollution Draft a framework tool for community-based assessments of black carbon emissions and health risks Educate local communities about black carbon emissions and risks The project’s initial phase, will entail a desk study; field work in Arctic communities, including particulate testing with aethalometers and community surveys to establish emission sources; an assessment report containing detailed findings and recommendations for mitigation, protecting public health and strengthening local institutional capacities; a draft framework assessment tool; and communication and outreach to a variety of key stakeholders.
An informative review: Alaska’s Eastern Interior Tribes stepping up to fill an existing atmospheric data gap
Aerosol surface data is nonexistent in the main river valleys of Interior Alaska. Baseline aerosol and meteorological surface data is vital for human health, prosperity, and ecosystem preservation in a rapidly changing world. A high concentration of aerosols, of diameter ≤ 2.5 micrometer, is linked to respiratory illnesses and contributes to health care costs. In Alaska, that includes air travel by charter. A system of aerosol monitors and meteorological ground stations are being placed and managed by the Tribes in four Yukon Flats villages. The Tribes of Beaver, Fort Yukon, Chalkyitsik, and Circle are stepping up to fill a gap in atmospheric surface data. The atmospheric data gap exists because research, in this sparsely populated area, has not been considered to benefit enough taxpayers to justify funding. These Tribal villages are strategically located adjacent to major river inlets into the Yukon Flats valley along the Porcupine and Yukon River between the mountain ranges of the Yukon Flats. Meteorological data of temperature, pressure, and relative humidity will be recorded at both 2 m and 10 m height. In addition, particle matter concentration, precipitation, and leaf wetness will be recorded at 2 m, while wind speed and direction, and total incoming radiation will be recorded at 10 m height. These meteorological and aerosol data can be interpreted in conjunction with satellite data, an emission inventory as well as HSPLIT backwards trajectories to determine the dynamic nature of aerosol flows and to trace the greatest anthropogenic contributors of aerosols within the Yukon Flats valley and individual villages. Within the villages, based on the research results, the Tribes can identify and address biomass, dusty road control programs, and fuel burning methods to mitigate health adverse air quality.
Air pollution health impact assessment: Previous work and considerations for Arctic-specific analyses
Air pollution is the fifth leading health risk factor globally. Communities in Arctic nations may be exposed to high levels of ambient and household air pollution from local sources, as well as air pollution transported from other regions. Previous studies have assessed the burden of disease from fine particulate matter (PM<sub>2.5</sub>) and ozone in Arctic communities as part of broader global or national assessments. More information is needed about health risks of PM<sub>2.5 </sub>and ozone in Arctic communities, considering local exposure levels, emission sources, and demographic and health characteristics of local populations. This talk addresses what is known about the air pollution health risks in Arctic countries, including health impacts of pollution transport to and from Arctic countries and health benefits of different mitigation approaches, as well as considerations for assessing health impacts of air pollution among Arctic communities with greater specificity.
Unprecedented summertime Arctic sea ice loss is opening the region to increased oil and gas extraction activities and ship traffic. Arctic aerosol emissions are expected to increase with increasing anthropogenic activities and production of sea spray aerosol. Given the complexity and evolving nature of atmospheric particles, as well as the challenges associated with Arctic measurements, significant uncertainties remain in our understanding of particle sources, evolution, and impacts in the Arctic. Long-term trends in aerosol size distributions at Utqiaġvik, Alaska show the significant influence of the Prudhoe Bay Oilfields on aerosol growth events, which are important for growing particles to sizes relevant to serve as cloud droplet nuclei. The chemical composition of fresh and aged combustion particles from the Prudhoe Bay Oilfields was examined through individual particle measurements during August-September 2015 and 2016 at Utqiaġvik and Oliktok Point, Alaska, respectively. An aerosol time-of-flight mass spectrometer (ATOFMS) and computer-controlled scanning electron microscopy with energy dispersive X-ray analysis were utilized to measure the size and chemical composition of individual particles associated with Prudhoe Bay air masses for the first time. Additionally, organic carbon, elemental carbon, black carbon, and inorganic ion concentrations, as well as size-resolved particle number concentrations, were measured to provide a comprehensive characterization of atmospheric aerosol chemical composition. During Utqiaġvik measurements, aerosol particle mixing states were observed to vary between Arctic Ocean and Prudhoe Bay influence, with significant secondary processing observed for the particles with air masses traveling from Prudhoe Bay, now the third largest oilfield in North America. The Oliktok Point field site is located within the Prudhoe Bay oilfields, and thus, elevated particle concentrations associated with soot particles were observed under direct combustion plume influence, with regional conditions associated with a mixture of aged sea spray, secondary organic aerosol, and combustion particles.
The Investigation of Multi-scale Processes Affecting Atmospheric Chemistry Transport (IMPAACT) is a proposed multi-pronged study to look at atmospheric chemistry in the Arctic and Pacific regions. The experiment will include an airborne component, likely in the year 2021, and a ground-based component that could begin sooner. Black carbon (BC) aerosol is a key climate forcing agent with some of the largest uncertainties with respect to transport, sources and deposition. So for this reason we propose a collaborative Pacific Rim network of observations focused on BC and other key tracers, especially CO, as part of IMPAACT. The observations along with high resolution chemical transport modeling will allow us to substantially improve our understanding of sources, transport, chemical processing and deposition in the Pacific and Arctic regions. Because BC has many definitions and an ambiguous chemical definition, it is essential that observations in this network be made with a consistent and comparable set of measurement techniques. For this work, we are interested to collaborate with other investigators to establish multiple sites around the Pacific Rim using comparable instrumentation and include one or two master sites where multiple techniques could be inter-compared. In this presentation we will describe key goals for this work, some thoughts on where stations could be located and the type of instrumentation that would be used.
Arctic Amplification is a phenomenon linked to complicated, non-linear processes and feedback mechanisms between surface and atmosphere in the Arctic regions. Aerosols are one of the largest sources of uncertainty for those processes and feedbacks due to spatial/temporal coverage and quality of the available observations. Aerosol optical properties, especially Aerosol Optical Thickness (AOT), over the Arctic are currently sparsely provided by ground-based measurements or active remote sensing observations with very limited spatial coverage for a relative short time period. Arctic aerosol observations from passive remote sensing are needed to fill the data gaps both temporally and spatially to reduce the uncertainty in the knowledge of Arctic aerosol during the recent Arctic amplification. Retrieval of AOT over snow-covered Arctic regions from passive remote sensing is very challenging due to 1) lack of aerosol information content; 2) large surface contribution to passive satellite observations; 3) similarities between snow and cloud properties. All above require precisely decoupling of surface contribution from Top Of Atmosphere (TOA) reflectance and good performance of cloud screening algorithm in advance. In this paper, we present a method for the AOT retrieval over snow/ice-covered surfaces trying to address all three aspects listed above utilizing a dual-viewing technique. Satellite-based MODIS and AATSR retrievals of AOT over snow-covered Arctic regions are in close agreement with ground-based measurements. Smooth transition of AOT between new-derived snow-covered regions AOT and mature oceanic regions AOT product is achieved, indicating trustable quality of the satellite derived AOT over Arctic regions. Arctic air pollution can be seen from space using the satellite-derived AOT product. Arctic haze event in spring is analyzed using the time-series dataset created by both satellite-derived and ground-based observations. A case study of the transportation of Russian wildfire in 2010 into the Arctic regions is also presented.
The climate warming effect of black carbon (BC) is amplified in the Arctic due to its deposition on light surfaces, decreasing reflectivity and hastening snow and ice melt. Monitoring indicates that Arctic atmospheric BC concentrations have declined by 40 % between 1990 and 2009. However, ca. 90 % of BC is wet-deposited in the Arctic and therefore mostly not recorded by atmospheric measurements. Consequently, atmospheric BC concentration and BC deposition trends may diverge. To get a comprehensive view on the climate impact of BC in the Arctic measurements of BC deposition are essential. Ice cores and lake sediments accumulate direct evidence of contamination deposition in chronological order. Despite their importance in deciphering the role of BC in Arctic climate change, relatively few deposition records exist at present. We analyzed a 300-year ice core from Svalbard and four 150-year lake sediment records from northern Finland. Unexpectedly, the ice core and lake sediment records show a pronounced increase in BC deposition from ca. 1970 to the present. The observed increase may be caused by within-Arctic emissions, such as Russian flaring. Additionally, chemical transport model results suggest that the increase may be caused by increased scavenging efficiency of BC due to increased temperatures and precipitation. These results contradict the prevailing understanding of declining BC values in the Arctic based on atmospheric monitoring, Greenland ice cores and modelling. The fact that a similar increasing BC deposition trend was recorded in two separate environmental archives receiving partly different atmospheric transport, highlights the plausibility of such a trend, and implies that it may also be observable at other Arctic locations. Thus, BC may have exerted a more significant Arctic warming impact than currently considered. More BC deposition records are urgently needed to comprehensively decipher the significance of BC in past, present and future Arctic climate change.
Comparing the effect of remote emissions and emerging local sources of Arctic pollution on Arctic aerosols and ozone and their impacts
Aerosol and ozone pollution in the Arctic predominantly originates from long-range pollution transport of anthropogenic and biomass burning emissions from the midlatitudes. However, local emission sources such as shipping and oil and gas extraction could already have an important local or regional influence on atmospheric composition and on the Arctic energy budget, even though this influence is not well characterized. In this work, we perform quasi-hemispheric simulations of aerosols and ozone in the Arctic with the WRF-Chem model. The model is used to evaluate and compare the impacts of midlatitude anthropogenic emissions, biomass burning, and local Arctic emissions (oil and gas, shipping) in terms of atmospheric composition, cloud/aerosol interactions, pollutant deposition and radiative forcing in the Arctic. Local Arctic emissions are expected to increase in the future due to Arctic warming and reduced sea ice cover. For this reason we also compare the impact of these different sources in 2050, for a future scenario with high Arctic shipping growth and decreasing midlatitude anthropogenic emissions.
Links between winter sea-ice retreat, mid-latitudes atmospheric circulation, and long range transport of black carbon in the Arctic
The ongoing shrinkage of the Arctic sea ice cover is likely linked to the global temperature rise, the amplified warming in the Arctic, and possibly weather anomalies in the mid-latitudes. By applying a novel statistical method in climate science, the Independent Component Analysis (ICA), to global atmospheric energy anomalies in winters from 1980 to 2015, we show the link between the sea ice melting in the Arctic and the combination of only three atmospheric oscillation patterns approximating observed spatial variations of near-surface temperature trends in winter. Two of these large scale atmospheric circulation patterns connect by independent dynamical processes the sea ice melting and related atmospheric perturbations in the mid-latitudes. At the same time, we investigated the possible feedbacks of these independent dynamical processes on the long range transport of pollutants from the mid-latitudes to the Arctic. We focused in particular on the transport and deposition on Arctic sea-ice of black carbon (BC) aerosol particles, which may further impact the regional and global climate, through direct radiative forcing and by modifying the snow and sea-ice albedo. Winter anomalies of meteorological fields from the global reanalysis are processed together with BC surface concentrations and deposition simulated by a general circulation model coupled with atmospheric chemistry and physics (ECHAM5-HAMMOZ). The feedback of winter sea-ice retreat and surface temperature warming on the transport of BC to the Arctic was quantified with Maximum Likelihood Estimates of atmospheric concentrations and deposition of BC in the Arctic associated to the three independent atmospheric patterns. We found that negative anomalies of the NAO likely favor the transport of BC in the upper troposphere, with small deposition over the Arctic sea-ice. Stable high pressure systems (atmospheric blocking) near Scandinavia favour the near surface transport directly from Western Europe towards the Barents Sea, with increasing deposition over the sea-ice.
Emissions from gas flaring have rarely been considered in global/regional emission inventories [Amann et al., 2013; Huang et al., 2015; Huang and Fu, 2016]. Flaring is a widely used approach of discharging and disposing of gaseous and liquid hydrocarbons through combustion at oil and gas production sites including oil wells, gas wells, offshore oil and gas rigs and landfills. Black carbon plays a unique role in the Arctic climate system due to its multiple effects. It causes Arctic warming by directly absorbing sunlight from space and by darkening the surface albedo of snow and ice, which indirectly leads to further warming and melting, thus inducing an Arctic amplification effect. We reconstruct BC emissions for Russian Federation, which is the country that has the largest area in the Arctic Circle. Local Russia information such as activity data, emission factors and other emission source data are used. The measurement done by Johnson, et al. 2017 suggested that individual flares BC emission rates can be spanned more than 4 orders of magnitude (up to 53.7 g/s). By using an advanced optical technique sky-LOSA (Line-Of-Sight Attenuation), the emission factor measured in the gas flaring field of Uzbekistan [Johnson et al., 2011] and Mexico [Johnson et al., 2013] was determined to be 2 ± 0.66 and 0.067 ± 0.02 g/s, respectively. We also update other emissions including power plant and transportation sources. Preliminary results of two-way H-CMAQ simulating the transport of BC particles to the Arctic will be updated. We will discuss how it causes radiative forcing changes over the Arctic.
Wet deposition of black carbon (BC) in the Arctic lowers snow albedo, thus contributing to warming in the Arctic. However, key processes and the magnitude of the effect of the BC deposition on radiative forcing in the Arctic are poorly understood due to uncertainties in the measurements of BC in snow. We measured the size distribution of BC in snowpack and falling snow using a single particle soot photometer combined with a nebulizer. We sampled snowpack at two sites (11 m and 300 m asl) at Ny-Ålesund, Spitsbergen, in April 2013. The BC size distributions did not show significant variations throughout the columns of the snowpack, suggesting stable size distributions in falling snow. The number and mass concentrations (C<sub>NBC</sub> and C<sub>MBC</sub>) at these sites agreed to within 19% and 10%, respectively, despite the sites’ difference in snow water equivalence. This indicates the small influence of the amount of precipitation on these quantities. We also sampled falling snow near the surface using a windsock during the same snow accumulation period. Column-averaged C<sub>NBC</sub> between snowpack and falling snow agreed to within 15%, after corrections for artifacts associated with the sampling of the falling snow. From the comparison of C<sub>NBC</sub> and C<sub>MBC</sub> in snowpack and falling snow, we estimated the relative contribution of dry deposition to total deposition to be about 22±6% at Ny-Ålesund during the snow accumulation period. C<sub>NBC</sub> in falling snow and BC mass concentrations in ambient air showed maxima in winter.
A decrease in precipitation during winter allows polluted air parcels from mid-latitudes to reach the Arctic. Low vertical mixing in the region concentrates aerosols and decreases scavenging. Aerosol impacts on cloud microphysical parameters remain poorly understood. However, cloud properties and pollution concentrations also vary with meteorological state, which poses the challenge of how to disentangle the impact of aerosols on clouds from that of natural thermodynamic variability. In this study we combine measurements from satellite instruments POLDER-3 and MODIS to temporally and spatially co-locate cloud properties over 65o in latitude with carbon monoxide concentrations, passive tracer of aerosol content, from GEOS-Chem between 2005 and 2010. We also add ERA-I reanalysis of meteorological parameters to stratify meteorological parameters, such as specific humidity and lower tropospheric stability. The goal is to determine the extent to which differences in cloud phase can be attributed to differences in aerosol content and not in meteorological parameters. We evaluated the degree of supercooling ΔT<sub>50</sub> that is required for 50% of a chosen ensemble of low- level clouds to be in the ice phase. Consistent with Rangno & Hobbs (2001), our results suggest that small droplet effective radii are related to high values of ΔT<sub>50</sub> . Also, anthropogenic pollution plumes lower the degree of supercooling by approximately 4°C, independent of the decrease in effective radius and change of meteorological regime. This effect of anthropogenic aerosol on the transition temperature to freezing has not been reported before to our knowledge and lacks clear explanation. Rangno, Arthur L., and Peter V. Hobbs. "Ice particles in stratiform clouds in the Arctic and possible mechanisms for the production of high ice concentrations." Journal of geophysical research 106 (2001): 15.
Regional aerosol emissions and temperature response: Local and remote climate impacts of regional aerosol forcing
Emissions of anthropogenic aerosols vary substantially over the globe and the short atmospheric residence time leads to a highly uneven radiative forcing distribution, both spatially and temporally. Regional aerosol radiative forcing can, nevertheless, exert a large influence on the temperature field away from the forcing region through changes in heat transport or the atmospheric or ocean circulation. The surface temperature distribution response to changes in sulfate aerosol forcing caused by sulfur dioxide (SO2) emission perturbations in four different regions is investigated using the Norwegian Earth System Model (NorESM). The four regions, Europe, North America, East and South Asia, are all regions with historically high aerosol emissions and are relevant from both an air-quality and climate policy perspective. All emission perturbations are defined relative to the year 2000 emissions provided for the Coupled Model Intercomparison Project phase 5. The global mean temperature change per unit SO2 emission change is similar for all four regions for similar magnitudes of emissions changes. However, the global temperature change per unit SO2 emission in simulations where regional SO2 emission were removed is substantially higher than that obtained in simulations where regional SO2 emissions were increased. Thus, the climate sensitivity to regional SO2 emissions perturbations depends on the magnitude of the emission perturbation in NorESM. On regional scale, the emission perturbations in different geographical locations lead to different regional temperature responses, both locally and in remote regions. The results from the model simulations are used to construct regional temperature potential (RTP) coefficients, which directly link regional aerosol or aerosol precursor emissions to the temperature response in different regions. These RTP coefficients can provide a simplified way to perform an initial evaluation of climate impacts of e.g. different emission policy pathways and pollution abatement strategies.