Abstract
Abstract. Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the “NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments” (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5∘ N, 62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 µgm-2day-1, north of 50∘ N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model–observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %–50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90 % of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semi-volatile species: the model–observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climate-relevant simulated summertime pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and cloud-albedo indirect (−0.4 W m−2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA.
Highlights
Aerosols play important roles in the summertime Arctic climate system
We used the GEOS-Chem-TwO-Moment Aerosol Sectional (TOMAS) chemical transport model with size-resolved aerosol microphysics to interpret measurements conducted during the summertime of 2016 in the Canadian Arctic Archipelago, some as part of the NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments (NETCARE) project (Abbatt et al, 2019)
We focused on examining the key processes that build summertime aerosol size distributions in this region, the role of Arctic marine secondary organic aerosol (AMSOA) condensation
Summary
Aerosols play important roles in the summertime Arctic climate system. Similar to their effects in other regions, aerosols interact directly with incoming solar radiation via scattering and absorption (Charlson et al, 1992; Hegg et al, 1996; Yu et al, 2006; Shindell and Faluvegi, 2009; Yang et al, 2014) and indirectly through the modification of cloud properties by acting as the seeds for cloud droplet formation (Lohmann and Feichter, 2005; McFarquhar et al, 2011). Observations indicate that aerosol particle formation and growth events occur frequently in the summertime Canadian Arctic Archipelago region between 60–100◦ W and 66– 85◦ N (Chang et al, 2011b; Leaitch et al, 2013; Willis et al, 2016, 2017; Croft et al, 2016b; Burkart et al, 2017a, b; Collins et al, 2017; Tremblay et al, 2019). Summertime Arctic aerosol size distributions are characterized by a suppressed accumulation mode (particles with diameters between 100 and 1000 nm) due to the efficient wet removal processes in frequently drizzling low clouds (Browse et al, 2014) and the limited transport from lower latitudes (Stohl, 2006; Law and Stohl, 2007; Korhonen et al, 2008)
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