New insights into aerosol and climate in the Arctic

Abstract

<p><strong>Abstract.</strong> Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013 . (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water and the overlying atmosphere in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source. (2) Evidence was found of widespread particle nucleation and growth in the marine boundary layer in the CAA in the summertime. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from sea bird colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic material (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol–climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow.</p>

A Factor and Trends Analysis of Multidecadal Lower Tropospheric Observations of Arctic Aerosol Composition, Black Carbon, Ozone, and Mercury at Alert, Canada

“…Aerosol acidity concentrations decreased by 76%, while sulfate decreased less by 52%. We suggest that, through the dehydration‐greenhouse feedback effect in Arctic winter ice clouds involving ice nucleation (Abbatt et al, ; Blanchet & Girard, ; Fisher et al, ; Girard et al, ), the observed increase in aerosol neutralization enhances ice formation (Abbatt et al, ) and ameliorates the infrared cooling caused by acidic sulfates at their peak in the 1980s.…”

“…In other words, the Alert aerosol showed an increase in neutralization associated with a shift from sulfuric acid to ammonium sulfate particles, due to a decline in SO 2 emissions relative to NH 3 emissions. One potential consequence of increased neutralization in the Arctic would be an increase in ice nuclei formation, which would ameliorate the infrared cooling effect of winter ice clouds associated with acidic arctic haze sulfates acting through the dehydration‐greenhouse feedback effect (Abbatt et al, ; Blanchet & Girard, ; Fisher et al, ; Girard et al, ).…”

“…Other studies expanded the existing knowledge of the summertime Arctic aerosol and the role of natural marine sources of particles in climate with a particular focus on organic components of the aerosol (e.g., Abbatt et al, ; Croft et al, ; Leaitch et al, ; Leaitch et al, ; Mungall et al, ; Sharma et al, ). Alert measurements were a vital part of Arctic Council assessments of impacts of black carbon on Arctic climate in support of policy development (AMAP, ) and Canadian Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments (Abbatt et al, ).…”

DMS emissions from the Arctic marginal ice zone

“…When sufficient sunlight crosses the sea ice or the free ocean surface, phytoplankton can also bloom in the water column, taking advantage of nutrient stocks replenished over the winter and stable stratification caused by ice melt. These pulses of sympagic and pelagic algal growth, largely dominated by diatom species, account for a major portion of annual primary production in polar waters (Perrette et al, 2011;Wassmann and Reigstad, 2011;Renaut et al, 2018) and result in the emission of a wide diversity of biogenic particles and gases to the atmosphere (Levasseur, 2013;Gabric et al, 2018;Abbatt et al, 2019).…”

“…Biogenic emissions play an important role in the Arctic climate in late spring and summer, when biological activity is maximal and the atmosphere is depleted of aerosols (both natural and anthropogenic; Abbatt et al, 2019). The low aerosol baseline, caused by limited transport from lower latitudes and efficient scavenging (Heintzenberg et al, 2015;Croft et al, 2016), favors secondary aerosol formation from local gaseous emissions (Leaitch et al, 2013;Collins et al, 2017).…”