Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago

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.

Shipborne observations reveal contrasting Arctic marine, Arctic terrestrial and Pacific marine aerosol properties

“…As stressed in Willis et al, (2018), NPF and growth is frequently observed in the boundary layer in the both Arctic open ocean and coastal regions. These events seem to occur more frequently than lower-latitude marine boundary layers (Quinn and Bates, 2011); there are multiple reasons including summer 24-h high solar radiation, low condensation sink, low temperature and low mixing of surface emissions, as recently reviewed in Abbatt et al (2019). Our study also confirmed that any NPF was not detected during the Pacific transect.…”

“…The high amount of DOC populating the sea-surface microlayer (SML) in the Arctic waters -including UV absorbing humic substances -can also produce VOCs (Ciuraru et al, 2015;Fu et al, 2015), which are known precursors of secondary organic aerosols. Recently, Mungall et al (2017) reported that the marine microlayer in the Canadian Arctic Archipelago is a source of oxidized VOCs (OVOCs), which could be an important source of biogenic secondary organic aerosol (Croft et al, 2019). Previous studies also reported fluorescent water-soluble organic aerosols in the High Arctic atmosphere (Fu et al, 2015).…”

Dimethyl sulfide and its role in aerosol formation and growth in the Arctic summer – a modelling study

“…Breider et al, 2017;Marelle et al, 2017). However, there are large uncertainties in the extrapolated ocean DMS climatology over the Arctic, particularly over the Canadian Polar Shelf and the Baffin Bay area due to the scarcity of measurements (Lana et al, 2011;Abbatt et al, 2019).…”

“…Figure 2 shows the Polar 6 flight tracks and the Amundsen cruise track during the NETCARE 2014 summer study. The measurements onboard Polar 6 took place from July 4 to 21, consisting of 11 research flights based from Resolute Bay, Nunavut; the measurements onboard Amundsen took place between July 13 and August 7 as the icebreaker sailed through the eastern Canadian Archipelago (Abbatt et al, 2019). Two independent measurements of DMS(g) were conducted on the Amundsen cruise using 1) a Hewlett Packard 5890 gas chromatograph (GC) fitted with a Sievers Model 355 sulfur chemiluminescence detector (SCD) from July 11 th to 24 th (hereafter referred to as GC-SCD; detection limit of 7 pptv) and 2) a high-resolution time-of-flight chemical ionization mass spectrometer, the Aerodyne HRToF-CIMS from July 15 th to August 7 th (hereafter referred to as CIMS; detection limit of 4 pptv).…”

“…annual average (Gourdal, et al, 2018;Abbatt et al, 2019). This additional source of DMS can have significant consequences for the Arctic aerosol, given the extensive coverage of melt ponds over first-year ice.…”