Description: Decreasing sea ice and increasing marine navigability in northern latitudes have changed Arctic ship traffic patterns in recent years and are predicted to increase annual ship traffic in the Arctic in the future. Development of effective regulations to manage environmental impacts of shipping requires an understanding of ship emissions and atmospheric processing in the Arctic environment. As part of the summer 2014 NETCARE (Network on Climate and Aerosols) campaign, the plume dispersion and gas and particle emission factors of effluents originating from the Canadian Coast Guard icebreaker Amundsen operating near Resolute Bay, NU, Canada, were investigated. The Amundsen burned distillate fuel with 1.5 wt% sulfur. Emissions were studied via plume intercepts using the Polar 6 aircraft measurements, an analytical plume dispersion model, and using the FLEXPART-WRF Lagrangian particle dispersion model. The first plume intercept by the research aircraft was carried out on 19 July 2014 during the operation of the Amundsen in the open water. The second and third plume intercepts were carried out on 20 and 21 July 2014 when the Amundsen had reached the ice edge and operated under ice-breaking conditions. Typical of Arctic marine navigation, the engine load was low compared to cruising conditions for all of the plume intercepts. The measured species included mixing ratios of CO2, NOx, CO, SO2, particle number concentration (CN), refractory black carbon (rBC), and cloud condensation nuclei (CCN). The results were compared to similar experimental studies in mid-latitudes. Plume expansion rates were calculated using the analytical model and found to be D0.75+0.81, 0.93+0.37, and 1.19+0.39 for plumes 1, 2, and 3, respectively. These rates were smaller than prior studies conducted at mid-latitudes, likely due to polar boundary layer dynamics, including reduced turbulent mixing compared to mid- latitudes. All emission factors were in agreement with prior observations at low engine loads in mid-latitudes. Ice-breaking increased the NOx emission factor from EFNOx 43.1+15.2 to 71.6+9.68 and 71.4+4.14 g kg-diesel-1 for plumes 1, 2, and 3, likely due to changes in combustion temperatures. The CO emission factor was EFCO 137+120, 12.5+3.70 and 8.13+1.34 g kg-diesel-1 for plumes 1, 2, and 3. The rBC emission factor was EFrBC D0.202+0.052 and 0.202+0.125 g kg-diesel-1 for plumes 1 and 2. The CN emission factor was reduced while ice-breaking from EFCN 2.41+0.47 to 0.45+0.082 and 0.507+0.037+1016 kg-diesel+1 for plumes 1, 2, and 3. At 0.6% supersaturation, the CCN emission factor was comparable to observations in mid-latitudes at low engine loads with EFCCN D3.03+0.933, 1.39+0.319, and 0.650+0.136+1014 kg-diesel-1 for plumes 1, 2, and 3.

Description: Size-resolved and vertical profile measurements of single particle chemical composition (sampling altitude range 50–3000 m) were conducted in July 2014 in the Cana- dian high Arctic during an aircraft-based measurement cam- paign (NETCARE 2014). We deployed the single parti- cle laser ablation aerosol mass spectrometer ALABAMA (vacuum aerodynamic diameter range approximately 200– 1000 nm) to identify different particle types and their mix- ing states. On the basis of the single particle analysis, we found that a significant fraction (23 %) of all analyzed parti- cles (in total: 7412) contained trimethylamine (TMA). Two main pieces of evidence suggest that these TMA-containing particles originated from emissions within the Arctic bound- ary layer. First, the maximum fraction of particulate TMA occurred in the Arctic boundary layer. Second, compared to particles observed aloft, TMA particles were smaller and less oxidized. Further, air mass history analysis, associated wind data and comparison with measurements of methane- sulfonic acid give evidence of a marine-biogenic influence on particulate TMA. Moreover, the external mixture of TMA- containing particles and sodium and chloride (“Na/Cl-”) containing particles, together with low wind speeds, sug- gests particulate TMA results from secondary conversion of precursor gases released by the ocean. In contrast to TMA- containing particles originating from inner-Arctic sources, particles with biomass burning markers (such as levoglucosan and potassium) showed a higher fraction at higher al- titudes, indicating long-range transport as their source. Our measurements highlight the importance of natural, marine inner-Arctic sources for composition and growth of summer- time Arctic aerosol.

Description: We present vertically resolved observations of aerosol composition during pristine summertime Arctic background conditions. The methansulfonic acid (MSA)-to-sulfate ratio peaked near the surface (mean 0.10), indicating a contribution from ocean-derived biogenic sulfur. Similarly, the organic aerosol (OA)-to-sulfate ratio increased toward the surface (mean 2.0). Both MSA-to-sulfate and OA-to-sulfate ratios were significantly correlated with FLEXPART-WRF-predicted air mass residence time over open water, indicating marine-influenced OA. External mixing of sea salt aerosol from a larger number fraction of organic, sulfate, and amine-containing particles, together with low wind speeds (median 4.7 m s−1), suggests a role for secondary organic aerosol formation. Cloud condensation nuclei concentrations were nearly constant (∼120 cm−3) when the OA fraction was 〈60% and increased to 350 cm−3 when the organic fraction was larger and residence times over open water were longer. Our observations illustrate the importance of marine-influenced OA under Arctic background conditions, which are likely to change as the Arctic transitions to larger areas of open water.

Description: Black carbon (BC) contributes to Arctic warm- ing, yet sources of Arctic BC and their geographic con- tributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Bar- row and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measure- ments at Alert. The springtime airborne measurements per- formed by the NETCARE campaign in 2015 and the PA- MARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and in- clude profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domes- tic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE 〈 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE = 17 %) except for an underestimation in the middle troposphere (500–700 hPa). Sensitivity simulations suggest that anthropogenic emis- sions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annu ally (37 %), with the largest contribution in the middle tropo- sphere (400–700 hPa). Anthropogenic emissions from north- ern Asia contribute considerable BC (27% in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually. At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20– 40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow. Our adjoint simulations indicate pronounced spatial het- erogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oil- fields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

Description: Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, Aerosol Robotic Network, and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at middle to high latitudes and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be −0.19 ± 0.09 Wm−2. This translates into an estimated global cooling of 0.05 to 0.12°C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.