Arctic air pollution: An overview of current knowledge

Transport of continental particulate over the Labrador Sea and entrainment are important pathways for glaciation of remote marine clouds

Marine Arctic clouds greatly influence the radiative balance across the Arctic region and their effectiveness at scattering radiation changes considerably depending on cloud phase. Glaciation of these clouds relies on the presence of ice nucleating particles, which are often limited in number, so often clouds may be liquid even at temperatures well below 0 °C. As the Arctic region warms, cloud feedbacks may accelerate change or lessen absorbed solar radiation. Understanding aerosol-cloud interactions and the sources and pathways of aerosol particles across the Arctic region is central to improving our knowledge of these poorly understood processes. In this paper, aircraft observations of single particle chemical and physical properties are presented and the composition of cloud residuals in both warm and glaciated clouds are examined using a single-particle laser ablation aerosol particle mass spectrometer (LAAPToF). In cloud, the LAAPToF sampled behind a Counterflow Virtual Impactor (CVI) to detect cloud particle residuals, separated into liquid, mixed phase and ice clouds using in situ observations of the fractional ice water content. Three different air mass regimes were sampled: northerly winds in both the marine boundary layer and the lower free troposphere; westerly winds from Canada in both the marine boundary layer and the free troposphere; and periods when the boundary layer winds were northerly but the air immediately above the boundary layer was from continental Canada. When the air in the boundary layer and free troposphere was from the north, most clouds were in the liquid phase, however, considerably more glaciation was observed when the air immediately above the boundary layer clouds was from Canada regardless of the flow direction in the boundary layer. Sea salt particles dominate the observed out of cloud aerosol particle population and liquid cloud particle residuals. However, in the detected mixed phase and ice cloud particle residuals dust and bioaerosol particles were substantial in number. Since these are known to be effective ice-nucleating particles, the observations suggest that long range transport of continental air and entrainment is an important pathway for the supply of aerosol to the remote Arctic boundary layer.

A comprehensive characterisation of natural aerosol sources in the high Arctic during the onset of sea ice melt

The interactions between aerosols and clouds are still one of the largest sources of uncertainty in quantifying anthropogenic radiative forcing. To reduce this uncertainty, we must first determine the baseline natural aerosol loading for different environments. In the pristine and hardly accessible polar regions, the exact nature of local aerosol sources remains poorly understood. It is unclear how oceans, including sea ice, control the aerosol budget, influence cloud formation, and determine the cloud phase. One critical question relates to the abundance and characteristics of biological aerosol particles that are important for the formation and microphysical properties of Arctic mixed-phase clouds. Within this work, we conducted a comprehensive analysis of various potential local sources of natural aerosols in the high Arctic over the pack ice during the ARTofMELT expedition in May-June 2023. Samples of snow, sea ice, seawater, and the sea surface microlayer (SML) were analysed for their microphysical, chemical, and fluorescent properties immediately after collection. Accompanied analyses of ice nucleating properties and biological cell quantification were performed at a later stage. We found that increased biological activity in seawater and the SML during the late Arctic spring led to higher emissions of fluorescent primary biological aerosol particles (fPBAPs) and other highly fluorescent particles (OHFPs, here organic-coated sea salt particles). Surprisingly, the concentrations of ice nucleating particles (INPs) in the corresponding liquid samples did not follow this trend. Gradients in OHFPs, fPBAPs, and black carbon indicated an anthropogenic pollution signal in surface samples especially in snow but also in the top layer of the sea ice core and SML samples. Salinity did not affect the aerosolisation of fPBAPs or sample ice nucleating activity. Compared to seawater, INP and fPBAP concentrations were enriched in sea ice samples. All samples showed distinct differences in their biological, chemical, and physical properties, which can be used in future work for an improved source apportionment of natural Arctic aerosol to reduce uncertainties associated with their representation in models and impacts on Arctic mixed-phase clouds.

Dominance of Plastic Emission in the High Arctic Aerosol in Light Spring

Arctic haze has attracted considerable scientific interest for decades. However, limited studies have focused on the molecular composition of atmospheric particulate matter that contributes to Arctic haze. Our study collected atmospheric particles at Alert in the Canadian high Arctic from mid-February to early May 2000. Over 100 organic species were identified in the solvent-extractable fraction by gas chromatography-mass spectrometry, which were grouped by their functional groups. Plasticizer-derived phthalates were the most abundant, followed by polyacids, sugars, sugar alcohols, biogenic SOA tracers, and fossil fuel combustion tracers. During the dark winter, major contributors to Arctic aerosols include plastic emissions, biomass burning, secondary oxidation products, and fossil fuel combustion products. In the light spring, phthalates (58-76% of the identified organics) dominated, followed by microbial and marine sources and secondary oxidation products. By employing a tracer-based method, we discovered that naphthalene and sesquiterpene oxidation products were the major contributors to SOC, and these contributions were much higher in the winter than in the spring. However, monoterpene and isoprene oxidation products peaked in light spring. Our results confirm that organic aerosols in the Arctic atmosphere are dominated by anthropogenic sources, which consist of both long-range-transported particles and combustion-emitted organics, as well as aged anthropogenic secondary organic aerosols. Despite decreasing anthropogenic pollution being replaced by natural emissions, plastic-derived pollution, represented by phthalates, increased significantly in the high Arctic atmosphere after the polar sunrise.

Clair JM, Dibb J, Temime-Roussel B, D’Anna B, Moon A, Alexander B, Yang Y, Nenes A, Mao J, Weber RJ. Hydroxymethanesulfonate and Sulfur(IV) in Fairbanks Winter During the ALPACA Study

Hydroxymethanesulfonate (HMS) in fine aerosol particles has been reported at significant concentrations along with sulfate under extreme cold conditions (-35 °C) in Fairbanks, Alaska, a high latitude city. HMS, a component of S(IV) and an adduct of formaldehyde and sulfur dioxide, forms in liquid water. Previous studies may have overestimated HMS concentrations by grouping it with other S(IV) species. In this work, we further investigate HMS and the speciation of S(IV) through the Alaskan Layered Pollution and Chemical Analysis (ALPACA) intensive study in Fairbanks. We developed a method utilizing hydrogen peroxide to isolate HMS and found that approximately 50% of S(IV) is HMS for total suspended particulates and 70% for PM2.5. The remaining unidentified S(IV) species are closely linked to HMS during cold polluted periods, showing strong increases in concentration relative to sulfate with decreasing temperature, a weak dependence on particle water, and similar particle size distributions, suggesting a common aqueous formation process. A portion of the unidentified S(IV) may originate from additional aldehyde-S(IV) adducts that are unstable in the water-based chemical analysis process, but further chemical characterization is needed. These results show the importance of organic S(IV) species in extreme cold environments that promote unique aqueous chemistry in supercooled liquid particles.

Canadian high arctic ice core records of organophosphate flame retardants and plasticizers

Organophosphate esters (OPEs) have been used as flame retardants, plasticizers, and anti-foaming agents over the past several decades. Of particular interest is the long range transport potential of OPEs given their ubiquitous detection in Arctic marine air. Here we report 19 OPE congeners in ice cores drilled on remote icefields and ice caps in the Canadian high Arctic. A multi-decadal temporal profile was constructed in the sectioned ice cores representing a time scale spanning the 1970s to 2014-16. In the Devon Ice Cap record, the annual total OPE (∑OPEs) depositional flux for all of 2014 was 81 μg m-2, with the profile dominated by triphenylphosphate (TPP, 9.4 μg m-2) and tris(2-chloroisopropyl) phosphate (TCPP, 42 μg m-2). Here, many OPEs displayed an exponentially increasing depositional flux including TCPP which had a doubling time of 4.1 ± 0.44 years. At the more northern site on Mt. Oxford icefield, the OPE fluxes were lower. Here, the annual ∑OPEs flux in 2016 was 5.3 μg m-2, dominated by TCPP (1.5 μg m-2) but also tris(2-butoxyethyl) phosphate (1.5 μg m-2 TBOEP). The temporal trend for halogenated OPEs in the Mt. Oxford icefield is bell-shaped, peaking in the mid-2000s. The observation of OPEs in remote Arctic ice cores demonstrates the cryosphere as a repository for these substances, and supports the potential for long-range transport of OPEs, likely associated with aerosol transport.

Rainwater chemistry composition in Bellsund: Sources of elements and deposition discrepancies in the coastal area (SW Spitsbergen, Svalbard)

Discrepancies in rainfall chemistry in Bellsund were found to be influenced by the orographic barrier and related to the variability in the inflow of air masses as well as to the distance of sampling sites from the sea and thus the extent of sea spray impact. This study covers measurements of rainfall (P) and air temperature (T), physicochemical parameters (pH, specific electrolytic conductivity (SEC), major ions (Cl^-, NO₃^-, SO₄^2-) and elements (Na, Ca, Mg,K), as well as trace elements (i.a. As, Cd, Cr, Fe, Co, Pb, Ni, Zn) and dissolved organic carbon (DOC) in 22 rainfall samples collected in August on the Calypsostranda marine terrace and in the forefield of a land-terminating glacier (NW Wedel Jarlsberg Land). The comparison of chemical parameters in the samples revealed major discrepancies, including statistically significant higher rainwater pH and SEC, and the levels of Ag, As, Bi, Ca, Co, Fe, Li, Mn, Mo, Ni, Pb, Sb, and V, deposited near the seashore (Calypsostranda) than in the glacier forefield. Cluster analysis (CA) showed that elements deposited in lower concentrations at the glacier forefield site came from predominately anthropogenic sources. Conversely, CA results of metals and metalloids deposited on the Calypsostranda marine terrace indicate both natural and anthropogenic sources. A correlation matrix and principal component analysis (PCA) permitted identifying two primary factors affecting rainfall chemistry at each of the study sites. In Calypsostranda, these were the inflow of relatively unpolluted cold air (F1 = 35.1%) and sea spray (F2 = 27.6%), while in the glacier forefield the factors were an orographic barrier (F1 = 37.3%) and the inflow of polluted warm air (F2 = 25.2%).

Ecological risk assessment of metals in the Arctic environment with emphasis on Kongsfjorden Fjord and freshwater lakes of Ny-Ålesund, Svalbard

The concentrations of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in the sediments, water, phytoplankton, zooplankton, and macroalgae from Kongsfjorden Fjord and the freshwater lakes of Ny-Ålesund in the Svalbard archipelago were determined in order to describe the anthropogenic impacts related to the Ny-Ålesund town. Water samples from nine stations, sediment samples from 23 stations, plankton samples from five stations, and six species of macroalgae were collected and subjected to heavy metal analysis using atomic absorption spectrophotometry (AAS). Only Cu and Zn were detected in the water samples. The plankton samples had only Zn, Cu, and Cr. The average metal concentrations in macroalgae fell in the decreasing order of Cu > Zn > Cr > Cd > Pb. In sediment samples, the metal order was as follows: Zn > Cu > Cr > Pb > Cd. Multivariate statistical analyses including principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to identify the source of the metal contamination. The metals were found to originate from a blend of both anthropogenic and geogenic sources. Pollution monitoring indices including geoaccumulation index (I_geo), contamination factor, contamination degree (C_deg), pollution load index (PLI), and potential ecological risk (PER) were calculated using the metal data. In the study area, I_geo values of the metals showed pollution grades from 0 (uncontaminated) to 6 (extremely contaminated). C_deg fell in classes from 1 (low contamination) to 4 (very high contamination). PLI values ranged between 0 and 5.68. PER values expressed that except for a few stations located at higher elevations in the glacial outwash plains, all other sites were highly polluted. The high level of pollution indices in the sites can be attributed to the anthropogenic activities persistent in the study area.

Impact of the initial hydrophilic ratio on black carbon aerosols in the Arctic

Black carbon (BC) contributes to patterns of Arctic warming, yet the initial hydrophilic ratio (IHR) of BC emitted from various sources and its impact on Arctic BC remain uncertain. With the use of a tagged tracer method of BC implemented in the global chemistry transport model GEOS-Chem, IHRs were partitioned into 7 BC combustion source categories according to the PKU-BC-v2 emission inventory. The results show that as the IHR increased, the concentration of BC decreased globally. The impact on Arctic BC was mainly reflected in the vertical profile and the burden rather than at the surface. Specifically, the greatest impact of IHR on Arctic BC appeared in summer, with the largest perturbation appearing at an altitude of approximately 600 hPa, reaching 8%. This change in BC vertical profile was mainly caused by the IHR change of wildfire combustion in Russia (44%) and Canada (51%), and the emissions from these two regions were also the two most important contributors to the BC concentration and burden in the middle and lower Arctic atmosphere in summer. In the other three seasons, anthropogenic combustion sources (oil, coal, and biomass) in East Asia, Russia, and Europe accounted for 19-40%, 14-28%, and 7-23%, respectively, of the monthly BC burden. Emissions from Russia were the most important contributor (27-43%) to the monthly BC surface concentration. Due to the large adjustment in IHR from 20% to 70%, biomass burning in Europe was shown to be the dominant contributor causing both burden (39%) and surface concentration (88%) changes in all seasons except summer.

Dissolved Metal (Fe, Mn, Zn, Ni, Cu, Co, Cd, Pb) and Metalloid (As, Sb) in Snow Water across a 2800 km Latitudinal Profile of Western Siberia: Impact of Local Pollution and Global Transfer

Snow cover is known to be an efficient and unique natural archive of atmospheric input and an indicator of ecosystem status. In high latitude regions, thawing of snow provides a sizable contribution of dissolved trace metals to the hydrological network. Towards a better understanding of natural and anthropogenic control on heavy metals and metalloid input from the atmosphere to the inland waters of Siberian arctic and subarctic regions, we measured chemical composition of dissolved (<0.22 µm) fractions of snow across a 2800 km south–north gradient in Western Siberia. Iron, Mn, Co, Ni, and Cd demonstrated sizable (by a factor of 4–7) decrease in concentration northward, which can be explained by a decrease in overall population density and the influence of dry aerosol deposition. Many elements (Mn, Ni, Cu, Cd, Pb, As, and Sb) exhibited a prominent local maximum (a factor of 2–3) in the zone of intensive oil and gas extraction (61–62° N latitudinal belt), which can be linked to gas flaring and fly ash deposition. Overall, the snow water chemical composition reflected both local and global (long-range) atmospheric transfer processes. Based on mass balance calculation, we demonstrate that the winter time atmospheric input represents sizable contribution to the riverine export fluxes of dissolved (<0.45 µm) Mn, Co, Zn, Cd, Pb, and Sb during springtime and can appreciably shape the hydrochemical composition of the Ob River main stem and tributaries.

A case study of PAH contamination using blue mussels as a bioindicator in a small Greenlandic fishing harbor

This study investigated the impact of local anthropogenic activity on the marine environment around the remote harbor of Qeqertarsuaq, West Greenland. Blue mussels (Mytilus sp.) were used as a bioindicator, and their physiological condition was found to decrease with increasing proximity to the harbor. Subsequently, the distribution of 19 polycyclic aromatic hydrocarbons (PAHs) and 9 groups of alkylated PAHs were measured in mussel and sediment samples. The highest values were found in a rocky collection area 15 m from a wooden pier frequented by small boats. A PAH source investigation, indicated a mixed source from light fuel oils and creosote used as boat coating. Finally, correlations between the mussels morphological condition and the PAH pollution were found to be significant for 4-, 5-, and 6-ring PAHs. In conclusion, the results indicate that pollution sources in harbors have significant effects on the local environment and should be considered in arctic conservation research.

Implementation and Impacts of Surface and Blowing Snow Sources of Arctic Bromine Activation Within WRF-Chem 4.1.1

Elevated concentrations of atmospheric bromine are known to cause ozone depletion in the Arctic, which is most frequently observed during springtime. We implement a detailed description of bromine and chlorine chemistry within the WRF-Chem 4.1.1 model, and two different descriptions of Arctic bromine activation: (1) heterogeneous chemistry on surface snow on sea ice, triggered by ozone deposition to snow (Toyota et al., 2011 https://doi.org/10.5194/acp-11-3949-2011), and (2) heterogeneous reactions on sea salt aerosols emitted through the sublimation of lofted blowing snow (Yang et al., 2008, https://doi.org/10.1029/2008gl034536). In both mechanisms, bromine activation is sustained by heterogeneous reactions on aerosols and surface snow. Simulations for spring 2012 covering the entire Arctic reproduce frequent and widespread ozone depletion events, and comparisons with observations of ozone show that these developments significantly improve model predictions during the Arctic spring. Simulations show that ozone depletion events can be initiated by both surface snow on sea ice, or by aerosols that originate from blowing snow. On a regional scale, in spring 2012, snow on sea ice dominates halogen activation and ozone depletion at the surface. During this period, blowing snow is a major source of Arctic sea salt aerosols but only triggers a few depletion events.

Concentrations of Major and Trace Elements within the Snowpack of Tyumen, Russia

A study on the composition of snow allowed for a quantitative determination of pollutants deposited from the atmosphere. Concentrations of dissolved (<0.45 μm) and particulate fractions of 62 chemical elements were determined by ICP–MS and ICP–AES in 41 samples of snow from Tyumen (Russia). The background sites were characterized by a predominance of the dissolved phase of elements, except for Al, Sn, Cr, Co and Zr. The increased concentrations of dissolved Cd, Cu, Zn, Pb, Ni, As and Mo can be explained by a long-range atmospheric transport from the sources located in the Urals. The urban sites showed multiple increases in particulate depositions and a predominance of the particulate phase, with a high degree of enrichment in many heavy metals. Sources of trace elements were determined according to the enrichment factor (EF). Highly enriched elements (Pb, Sb, Cd, Ag, Mo, As, Zn and Cu) with an EF > 100 were emitted from anthropogenic sources. According to the potential ecological risk index (RI), the worst ecological conditions were identified in Tyumen’s historical center, industrial zone and along roads with the heaviest traffic. The data obtained in the present study allowed us to identify the most polluted parts of the city, which are located in the center and along the roads with the most intensive traffic. This research could offer a reference for the atmospheric pollution prevention and control in Tyumen.

Data Assimilation of AOD and Estimation of Surface Particulate Matters over the Arctic

In this study, more accurate information on the levels of aerosol optical depth (AOD) was calculated from the assimilation of the modeled AOD based on the optimal interpolation method. Additionally, more realistic levels of surface particulate matters over the Arctic were estimated using the assimilated AOD based on the linear relationship between the particulate matters and AODs. In comparison to the MODIS observation, the assimilated AOD was much improved compared with the modeled AOD (e.g., increase in correlation coefficients from −0.15–0.26 to 0.17–0.76 over the Arctic). The newly inferred monthly averages of PM10 and PM2.5 for April–September 2008 were 2.18–3.70 μg m−3 and 0.85–1.68 μg m−3 over the Arctic, respectively. These corresponded to an increase of 140–180%, compared with the modeled PMs. In comparison to in-situ observation, the inferred PMs showed better performances than those from the simulations, particularly at Hyytiala station. Therefore, combining the model simulation and data assimilation provided more accurate concentrations of AOD, PM10, and PM2.5 than those only calculated from the model simulations.

Investigation of black carbon climate effects in the Arctic in winter and spring

Black carbon (BC) exerts a potential influence on climate, especially in the Arctic, where the environment is very sensitive to climate change. Therefore, the study of climate effects of BC in this region is particularly important. In this study, numerical simulations were performed using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in the Arctic in winter and spring for two years to investigate the atmospheric BC causing changes in surface radiation, meteorology, and atmospheric stability. Generally, WRF-Chem well reproduced the temporal variations of meteorological variables and BC concentration. Numerical simulations showed that BC concentrations in the Arctic in winter were mostly higher than those in spring, and the BC-induced near-surface temperature changes were also stronger. The effects of BC on near-surface water vapor mixing ratio were consistent with the spatial pattern of near-surface temperature changes. That was probably the result of the regional circulation anomaly due to the temperature changes. Additionally, the distributions of near-surface temperature changes and horizontal wind changes also reflected in the distribution of planetary boundary layer height. Ultimately, this study revealed that the downward longwave radiation related to cloudiness changes played an important role for driving near-surface temperature in the Arctic in winter. While in spring, the relatively less changes in near-surface temperature may be the result of the mutual compensation between the surface longwave and shortwave radiation effects.

Arctic snow pollution: A GC-HRMS case study of Franz Joseph Land archipelago

Anthropogenic pollution of the Arctic atmosphere is of great interest due to the vulnerability of the Arctic ecosystems, as well as the processes of global transport and accumulation of atmospheric aerosols at high latitudes under conditions of cold climate. The present work throws light upon chemical composition of Arctic snow as a natural deposition matrix for atmospheric semi-volatile pollutants taken from the northernmost Arctic archipelago - Franz Josef Land, which is least affected by local sources of pollution and being a unique unstudied environmental object. The used methodology involved the liquid-liquid extraction of snow samples with dichloromethane and combination of targeted and non-targeted analyses of semi-volatile organic compounds with comprehensive two-dimensional gas chromatography - high-resolution mass spectrometry. While almost none of the known priority pollutants (except three dialkylphthalates) were identified in the studied samples, non-targeted screening revealed a specific class of biomass burning biomarkers - fatty amides with oleamide being the major component among them. Some peculiar organic pollutants (N,N-dimethylcyclohexylamine and N,N-dimethylbenzylamine) were identified in few samples. First results on the semi volatile pollutants in Franz Joseph Land snow were obtained using the most reliable GC × GC-HRMS non-target analysis.

Investigation of distribution, transportation, and impact factors of atmospheric black carbon in the Arctic region based on a regional climate-chemistry model

Black carbon (BC) as the main component of pollutants in the Arctic plays an important role on regional climate change. In this study, we applied the regional climate-chemistry model, WRF-Chem, to investigate the spatial distribution, transportation, and impact factors of BC in the Arctic. Compared with reanalysis data and observations, the WRF-Chem performed well in terms of the seasonal variations of meteorological parameters and BC concentrations, indicating the applicability of this model on Arctic BC simulation works. Our results showed that the BC concentrations in the Arctic had an obviously seasonalvariation pattern. Surface BC concentrations peaked during winter and spring seasons, while the minimum occurred during summer and autumn seasons. For the vertical distribution, BC aerosols mainly concentrated in the Arctic lower troposphere, and most of BC distributed near the surface during winter and spring seasons and in the higher altitude during other seasons. The seasonality of BC was associated with the seasonal change of meteorological field. During winter, the significant northward airflow prevailing in northern Eurasia caused the transport of accumulated pollutants from this region into the Arctic. The similar but weakened northward airflow pattern and the anticyclone activity during spring can allow pollutants to be transported to the Arctic lower troposphere. Moreover, the more stable atmosphere during winter and spring seasons made BC accumulated mainly near the surface. During summer and autumn seasons, the less stable boundary layer and the cyclone activity in the Arctic facilitated the diffusion of pollutants into the higher altitude. Meanwhile, the higher relative humidity can promote the wet removal process and lead to the relatively lower BC concentrations near the surface. Compared with the seasonal change of emission, our analysis showed that the seasonal variation of meteorological field was the main contributor for the seasonality of BC in the Arctic.

Particle-Size Variability of Aerosol Iron and Impact on Iron Solubility and Dry Deposition Fluxes to the Arctic Ocean

This study provides unique insights into the properties of iron (Fe) in the marine atmosphere over the late summertime Arctic Ocean. Atmospheric deposition of aerosols can deliver Fe, a limiting micronutrient, to the remote ocean. Aerosol particle size influences aerosol Fe fractional solubility and air-to-sea deposition rate. Size-segregated aerosols were collected during the 2015 US GEOTRACES cruise in the Arctic Ocean. Results show that aerosol Fe had a single-mode size distribution, peaking at 4.4 µm in diameter, suggesting regional dust sources of Fe around the Arctic Ocean. Estimated dry deposition rates of aerosol Fe decreased from 6.1 µmol m⁻² yr⁻¹ in the areas of ~56°N–80°N to 0.73 µmol m⁻² yr⁻¹ in the areas north of 80°N. Aerosol Fe solubility was higher in fine particles (<1 µm) which were observed mainly in the region north of 80°N and coincided with relatively high concentrations of certain organic aerosols, suggesting interactions between aerosol Fe and organic ligands in the high-latitude Arctic atmosphere. The average molar ratio of Fe to titanium (Ti) was 2.4, substantially lower than the typical crustal ratio of 10. We speculate that dust sources around the Arctic Ocean may have been altered because of climate warming.

Mercury Pollution in the Arctic from Wildfires: Source Attribution for the 2000s

Atmospheric mercury (Hg) is a global environmental pollutant, with wildfire emissions being an important source. There have been growing concerns on Hg contamination in the Arctic region, which is largely attributed to long-range transport from lower latitude regions. In this work, we estimate the contributions of wildfire emissions from various source regions to Hg pollution in the Arctic (66° N to 90° N) using a newly developed global Hg wildfire emissions inventory and an atmospheric chemical transport model (GEOS-Chem). Our results show that global wildfires contribute to about 10% (15 Mg year^-1) of the total annual Hg deposition to the Arctic, with the most important source region being Eurasia, which contribute to 5.3% of the total annual Hg deposition followed by Africa (2.5%) and North America (1%). The substantial contributions from the Eurasia region are driven by the strong wildfire activity in the boreal forests. The total wildfire-induced Hg deposition to the Arctic amounts to about one-third of the deposition caused by present-day anthropogenic emissions. We also find that wildfires result in significant Hg deposition to the Arctic across all seasons (winter: 8.3%, spring: 7%, summer: 11%, and fall: 14.6%) with the largest deposition occurring during the boreal fire season. These findings indicate that wildfire is a significant source for Arctic Hg contamination and also demonstrate the importance of boreal forest in the global and regional Hg cycle through the mobilization of sequestered Hg reservoir.

The Effect of Arctic Dust on the Retrieval of Satellite Derived Sea and Ice Surface Temperatures

Large quantities of dust are transported annually to the Arctic, primarily from Asian deserts. The influx of dust into the polar environment changes the radiative properties of clouds while the deposition of dust onto ice and snow decreases the surface albedo. Atmospheric and surface dust may be identified with space borne radiometers by comparing infrared energy in the 11 μm and 12 μm regime. Between 2007 and 2017 satellite infrared data revealed persistent low-level dust clouds in the vicinity of Amundsen Gulf in the Western Canadian Arctic during the melting season. Evidence suggests that the subsequent deposition of atmospheric dust in the region affected the surface emissivity in the thermal infrared regime. As a result, satellite derived sea and ice surface temperature algorithms were rendered inaccurate in these areas. Moreover, the ubiquitous nature of dust in the region may play a role in the rapidly vanishing cryosphere.

Raman lidars for a better understanding of pollution in the Arctic System (PARCS)

The development of oil and gas drilling and the opening of new shipping routes, in the Barents and Norway seas, poses new challenges for the Arctic environment due to the impact of air pollution emissions on climate and air quality. To improve our knowledge of the interactions between aerosols, water vapor and cloud cover, within the French PARCS (Pollution in the ARCtic System) project, Raman lidar observations were performed from the ground and from an ultra-light aircraft near the North Cape in northern Norway, and coupled with measurements from a 95 GHz ground-based Doppler radar.

Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones, Carboxylic Acids, and Trace Metals in Arctic Aerosols: Long-Range Atmospheric Transport, Photochemical Degradation/Production at Polar Sunrise

The distributions, correlations, and source apportionment of aromatic acids, aromatic ketones, polycyclic aromatic hydrocarbons (PAHs), and trace metals were studied in Canadian high Arctic aerosols. Nineteen PAHs including minor sulfur-containing heterocyclic PAH (dibenzothiophene) and major 6 carcinogenic PAHs were detected with a high proportion of fluoranthene followed by benzo[k]fluoranthene, pyrene, and chrysene. However, in the sunlit period of spring, their concentrations significantly declined likely due to photochemical decomposition. During the polar sunrise from mid-March to mid-April, benzo[a]pyrene to benzo[e]pyrene ratios significantly dropped, and the ratios diminished further from late April to May onward. These results suggest that PAHs transported over the Arctic are subjected to strong photochemical degradation at polar sunrise. Although aromatic ketones decreased in spring, concentrations of some aromatic acids such as benzoic and phthalic acids increased during the course of polar sunrise, suggesting that aromatic hydrocarbons are oxidized to result in aromatic acids. However, PAHs do not act as the major source for low molecular weight (LMW) diacids such as oxalic acid that are largely formed at polar sunrise in the arctic atmosphere because PAHs are 1 to 2 orders of magnitude less abundant than LMW diacids. Correlations of trace metals with organics, their sources, and the possible role of trace transition metals are explained.

Arctic sea ice melt leads to atmospheric new particle formation

Atmospheric new particle formation (NPF) and growth significantly influences climate by supplying new seeds for cloud condensation and brightness. Currently, there is a lack of understanding of whether and how marine biota emissions affect aerosol-cloud-climate interactions in the Arctic. Here, the aerosol population was categorised via cluster analysis of aerosol size distributions taken at Mt Zeppelin (Svalbard) during a 11 year record. The daily temporal occurrence of NPF events likely caused by nucleation in the polar marine boundary layer was quantified annually as 18%, with a peak of 51% during summer months. Air mass trajectory analysis and atmospheric nitrogen and sulphur tracers link these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. The occurrence of such events across a full decade was anti-correlated with sea ice extent. New particles originating from open water and open pack ice increased the cloud condensation nuclei concentration background by at least ca. 20%, supporting a marine biosphere-climate link through sea ice melt and low altitude clouds that may have contributed to accelerate Arctic warming. Our results prompt a better representation of biogenic aerosol sources in Arctic climate models.

Concentrations of trace elements and iron in the Arctic soils of Belyi Island (the Kara Sea, Russia): patterns of variation across landscapes

The concentrations of several trace elements and iron were determined in 26 soil samples from Belyi Island in the Kara Sea (West Siberian sector of Russian Arctic). The major types of soils predominating in the soil cover were sampled. The concentrations of trace elements (mg kg^-1) varied within the following ranges: 119-561 for Mn, 9.5-126 for Zn, 0.082-2.5 for Cd, <0.5-19.2 for Cu, <0.5-132 for Pb, 0.011-0.081 for Hg, <0.5-10.3 for Co, and 7.6-108 for Cr; the concentration of Fe varied from 3943 to 37,899 mg kg^-1. The impact of particular soil properties (pH, carbon and nitrogen contents, particle-size distribution) on metal concentrations was analyzed by the methods of correlation, cluster, and factor analyses. The correlation analysis showed that metal concentrations are negatively correlated with the sand content and positively correlated with the contents of silt and clay fractions. The cluster analysis allowed separation of the soils into three clusters. Cluster I included the soils with the high organic matter content formed under conditions of poor drainage; cluster II, the low-humus sandy soils of the divides and slopes; and cluster III, saline soils of coastal marshes. It was concluded that the geomorphic position largely controls the soil properties. The obtained data were compared with data on metal concentrations in other regions of the Russian Arctic. In general, the concentrations of trace elements in the studied soils were within the ranges typical of the background Arctic territories. However, some soils of Belyi Island contained elevated concentrations of Pb and Cd.

Do morphometric parameters and geological conditions determine chemistry of glacier surface ice? Spatial distribution of contaminants present in the surface ice of Spitsbergen glaciers (European Arctic)

The chemism of the glaciers is strongly determined by long-distance transport of chemical substances and their wet and dry deposition on the glacier surface. This paper concerns spatial distribution of metals, ions, and dissolved organic carbon, as well as the differentiation of physicochemical parameters (pH, electrical conductivity) determined in ice surface samples collected from four Arctic glaciers during the summer season in 2012. The studied glaciers represent three different morphological types: ground based (Blomlibreen and Scottbreen), tidewater which evolved to ground based (Renardbreen), and typical tidewater glacier (Recherchebreen). All of the glaciers are functioning as a glacial system and hence are subject to the same physical processes (melting, freezing) and the process of ice flowing resulting from the cross-impact force of gravity and topographic conditions. According to this hypothesis, the article discusses the correlation between morphometric parameters, changes in mass balance, geological characteristics of the glaciers and the spatial distribution of analytes on the surface of ice. A strong correlation (r = 0.63) is recorded between the aspect of glaciers and values of pH and ions, whereas dissolved organic carbon (DOC) depends on the minimum elevation of glaciers (r = 0.55) and most probably also on the development of the accumulation area. The obtained results suggest that although certain morphometric parameters largely determine the spatial distribution of analytes, also the geology of the bed of glaciers strongly affects the chemism of the surface ice of glaciers in the phase of strong recession.

Seasonality of global and Arctic black carbon processes in the Arctic Monitoring and Assessment Programme models

This study quantifies black carbon (BC) processes in three global climate models and one chemistry transport model, with focus on the seasonality of BC transport, emissions, wet and dry deposition in the Arctic. In the models, transport of BC to the Arctic from lower latitudes is the major BC source for this region. Arctic emissions are very small. All models simulated a similar annual cycle of BC transport from lower latitudes to the Arctic, with maximum transport occurring in July. Substantial differences were found in simulated BC burdens and vertical distributions, with Canadian Atmospheric Global Climate Model (CanAM) (Norwegian Earth System Model, NorESM) producing the strongest (weakest) seasonal cycle. CanAM also has the shortest annual mean residence time for BC in the Arctic followed by Swedish Meteorological and Hydrological Institute Multiscale Atmospheric Transport and Chemistry model, Community Earth System Model, and NorESM. Overall, considerable differences in wet deposition efficiencies in the models exist and are a leading cause of differences in simulated BC burdens. Results from model sensitivity experiments indicate that convective scavenging outside the Arctic reduces the mean altitude of BC residing in the Arctic, making it more susceptible to scavenging by stratiform (layer) clouds in the Arctic. Consequently, scavenging of BC in convective clouds outside the Arctic acts to substantially increase the overall efficiency of BC wet deposition in the Arctic, which leads to low BC burdens and a more pronounced seasonal cycle compared to simulations without convective BC scavenging. In contrast, the simulated seasonality of BC concentrations in the upper troposphere is only weakly influenced by wet deposition in stratiform clouds, whereas lower tropospheric concentrations are highly sensitive.

Unrealistically pristine air in the Arctic produced by current global scale models

Black carbon aerosol (BCA) in the Arctic has profound impacts on the global climate system through radiation processes. Despite its enormous impacts, current global scale models, powerful tools for estimating overall impact, tend to underestimate the levels of BCA in the Arctic over several seasons. Using a global aerosol transport simulation with a horizontal grid resolution of 3.5 km, we determined that a higher resolution significantly reduced the underestimation of BCA levels in the Arctic, mainly due to an enhancement of the representation of low-pressure and frontal systems. The BCA mass loading in the Arctic simulated with 3.5-km grid resolution was 4.2-times larger than that simulated with coarse (56-km) grid resolution. Our results also indicated that grid convergence had not occurred on both the contrast between the cloud/cloud free areas and the poleward BCA mass flux, despite the use of the 3.5-km grid resolution. These results suggest that a global aerosol transport simulation using kilometre-order or finer grid resolution is required for more accurate estimation of the distribution of pollutants in the Arctic.

Trace metal distribution in pristine permafrost-affected soils of the Lena River delta and its hinterland, northern Siberia, Russia

Abstract. Soils are an important compartment of ecosystems and have the ability to buffer and immobilize substances of natural and anthropogenic origin to prevent their movement to other environment compartments. Predicted climatic changes together with other anthropogenic influences on Arctic terrestrial environments may affect biogeochemical processes enhancing leaching and migration of trace elements in permafrost-affected soils. This is especially important since Arctic ecosystems are considered to be highly sensitive to climatic changes as well as to chemical contamination. This study characterises background levels of trace metals in permafrost-affected soils of the Lena River delta and its hinterland in northern Siberia (73.5–69.5° N), representing a remote region far from evident anthropogenic trace metal sources. Investigations on the element content of iron (Fe), arsenic (As), manganese (Mn), zinc (Zn), nickel (Ni), copper (Cu), lead (Pb), cadmium (Cd), cobalt (Co), and mercury (Hg) in different soil types developed in different geological parent materials have been carried out. The highest median concentrations of Fe and Mn were observed in soils belonging to ice-rich permafrost sediments formed during the Pleistocene (ice-complex) while the highest median values of Ni, Pb and Zn were found in soils of both the ice-complex and the Holocene estuarine terrace of the Lena River delta region, as well as in the southernmost study unit of the hinterland area. Detailed observations of trace metal distribution on the micro scale showed that organic matter content, soil texture and iron-oxide contents influenced by cryogenic processes, temperature, and hydrological regimes are the most important factors determining the metal abundance in permafrost-affected soils. The observed range of trace element background concentrations was similar to trace metal levels reported for other pristine northern areas.

Chronology of Pu isotopes and 236U in an Arctic ice core

In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 μBq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores.

High-resolution, continuous method for measurement of acidity in ice cores

The acid content of ice core samples provides information regarding the history of volcanism, biogenic activity, windblown dust, forest fires, and pollution-induced acid rain. A continuous ice core analysis allows for collection of high-resolution data in a very efficient manner, but this technique has not been readily applied to the measurement of pH and acidity in ice cores. The difficulty arises because the sample is highly undersaturated with respect to carbon dioxide (CO(2)) immediately after melting, making it difficult to maintain stable concentrations of dissolved carbon dioxide and carbonic acid (H(2)CO(3)). Here, we present a solution to this problem in the form of a small flow-through bubbling chamber that is supplied with a known concentration of CO(2). The bubbling action allows for quick equilibration while the small size of the chamber limits sample mixing in order to maintain high resolution. Thorough error analysis provides a measurement uncertainty of ±0.20 μM or ±5% of the acidity value, whichever is greater, and the T95 signal response time is determined to be 1.25 min. The performance of the technique is further evaluated with data from a 63-year ice core from northwest Greenland for which all major ion species were also measured. The measured acidity closely matches the acidity derived from a charge balance calculation, indicating that all of the analytes were measured accurately. The performance specifications that we provide are applicable to ice cores with low concentrations of alkaline dust (<500 ppb), which includes the vast majority of ice cores that are collected. To date, the method has not been evaluated with samples containing high alkaline dust concentrations, such as Greenland cores from the last glacial period, where measurement could be made difficult by memory effects as particles coat the internal surfaces of the sample stream.

Effects of Acid rain on freshwater ecosystems

Acid-vulnerable areas are more numerous and widespread than believed 7 years ago. Lakes and streams in acid-vulnerable areas of northeastern North America have suffered substantial declines in acid-neutralizing capacity, the worst cases resulting in biological damage. Many invertebrates are very sensitive to acidification, with some disappearing at pH values as high as 6.0. However, the recent rate of acidification of lakes is slower than once predicted, in part the result of decreases in sulfur oxide emissions. A discussion of some of the processes that have contributed to the acidification of lakes as well as those that have protected acid-sensitive freshwaters is presented. The author is in the Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada.