Climate change is more severe in the Arctic than the lower latitudes, and the rapid warming has the potential to influence the ocean, land and atmospheric interactions (IPCC, 2013). Given the Arctic sensitivity to climate change, aerosol particles are among the important climate forcing agents in this region, with a net cooling effect and offsetting around 60% of the greenhouse gas warming (Najafi et al., 2015;Stuecker et al., 2018).Aerosols can influence climate directly, by absorbing and scattering sunlight, and indirectly, by modifying cloud properties (Haywood & Boucher, 2000). The formation of clouds depends on the presence and availability of aerosol particles to uptake or condense water vapor at a given supersaturation. These particles are known as cloud condensation nuclei (CCN). Indirect effects of aerosols include their impact on cloud microphysical processes (first indirect effect-, cloud-albedo or Twomey effect) (Twomey, 1977), and cloud lifetime (second indirect effect-Albrecht effect) (Albrecht, 1989). Despite the importance of aerosol indirect effects, key uncertainties remain in the cloud radiative processes, and a better understanding of the Arctic aerosol-clouds interaction and its effect on the surface radiative flux is needed (Boucher et al., 2013;Kay et al., 2011;Shupe and Intrieri, 2004). Specifically, thermodynamic state, cloud base height and cloud microphysics, such as number concentrations/size/shapes/ phases of aerosol/droplets, are the factors that strongly influence the cloud radiative effects (Chen et al., 2006;Coopman et al., 2018;Rosenfeld et al., 2019). The impact of atmospheric chemistry connecting emissions to aerosols and hence to these radiative effects are thus of interest.Aerosols observed in the Arctic during winter and spring, including particulate organic matter, nitrate, sulfate and black carbon, mostly originate from North America and Eurasia (Sirois and Barrie, 1999;Stone et al., 2014). Using four years of ground-based aerosol and radiation measurements based on Barrow and Alsaka, Garrett and Zhao (2006) showed an increase of the longwave emissivity and the presence of thin water clouds, due to the influence of pollution from mid-latitudes, especially during winter and spring when the long-range transport from lower latitudes to the Arctic is more prevalent. Coopman et al. (2016) examined solely anthropogenic pollution impacts on the low-level Arctic liquid clouds for a period between 2008 and 2010, and found the net aerosol-cloud interaction (ACI net ) values are sensitive to the pollution plumes originating from long-range transport.
<p>Atmospheric dimethyl sulfide, DMS, is the main biogenic source of sulfate particles in the Arctic atmosphere. Sulfate particles have a net cooling effect, which can partially offset Arctic warming from absorbing aerosols, such as black carbon. As efficient cloud condensation nuclei (CCN), sulfate particles are also able to influence the cloud&#8217;s microphysical properties.&#160;</p> <p>DMS production and emission to the atmosphere increase during the Arctic summer, due to a greater ice-free sea surface area and higher biological activity. In the model simulation of a field campaign conducted over the Canadian high Arctic during the summer of 2014 (NETCARE; Abbatt et al. 2019), the inclusion of DMS in the model, GEM-MACH, resulted in a significant increase, up to 100%, in the modelled atmospheric SO<sub>2</sub>&#160;in some regions of the Canadian Arctic. Analysis of the modelled size-segregated aerosol sulfate indicated that DMS has the most significant impact on particles in the size range of 50 &#8211; 200 nm in this case. Simulations have shown that localized regions of high seawater DMS can have a significant impact on atmospheric concentrations.</p> <p>Further investigation of DMS impact on the Arctic summer cloud microphysics was carried out by using a fully coupled version of GEM-MACH. Overall, the model simulations show that the inclusion of DMS in model leads to an increase in cloud droplet number concentrations (CDNC) and a decrease in droplet mean mass diameters (MMD), and has no significant effects on liquid water content (LWC). The impact of DMS on Canadian weather forecasts will be evaluated using operational forecast tools.</p>
<p>Multiple simulations were conducted using Environment and Climate Change Canada&#8217;s Global Environmental Multiscale-Modelling Air-quality and CHemistry (GEM-MACH) in order to evaluate the model&#8217;s predictive capabilities for concentrations, height of plume emissions, and deposition for regions within and downwind of the Canadian Oil Sands.&#160; The innermost domain of the nested setup was 1350x1345 km in extent, centered on the Canadian provinces of Alberta and Saskatchewan, with a grid-cell size of 2.5 km.&#160; Successive model science updates were carried out in a series of 15-month simulations covering the period August 1, 2017 through October 31, 2018.&#160; The simulations were compared to local (Wood Buffalo Environmental Association, Lakeland Industry and Community Association, Peace River Area Monitoring Program), provincial (Alberta Precipitation Quality Monitoring Program (APQMP)), and national (National Air Pollution Surveillance (NAPS) and Canadian Air and Precipitation Monitoring Network (CAPMoN)) monitoring network data for the entire period, as well as to aircraft and ground-based measurement intensive data from August 2017, April 2018 and June to July 2018.&#160;</p><p>The series of simulations included successive updates to the model&#8217;s gas-phase chemistry, secondary organic aerosol formation, photolysis rate calculations, particle speciation, plume rise, inorganic heterogeneous chemistry, cloud processing of gases and aerosols, gas reactions on particle surfaces, the addition of a tracer for the emissions, transport and deposition of total organic carbon gas, the addition of H<sub>2</sub>S as a transported species, and numerous updates to the model&#8217;s input emissions making use of inventory and observation-based emissions.&#160; While the model evaluation is still underway, the evaluation thus far has identified key chemical and physical processes relevant to the Oil Sands area, which will be highlighted in this presentation, including:</p><p>(1) Concentrations of particulate base cations are dominated by fugitive dust, , and exhibit strong seasonality (higher in summer than winter).&#160; This seasonality can be reasonably well simulated by the model if coarse mode emissions of fugitive dust are shut off at temperatures slightly below the freezing point of water;</p><p>(2) Low biased model surface ozone predictions from January through April are potentially due to insufficient simulated Troposphere / Stratosphere exchange, in turn identifying the process as a driver for springtime ozone in the area;</p><p>(3) The concentrations of NO<sub>2</sub>, particulate matter and nitric acid are all linked via a combination of surface reactions transforming NO<sub>2</sub> to HONO and HNO<sub>3</sub>, and inorganic heterogeneous chemistry, with the former reaction probabilities being highly uncertain;</p><p>(4) Aircraft-based estimates of total organic carbon gas emissions and deposition used as a tracer within the model suggest high molecular mass hydrocarbons are emitted as gases from OS facilities and are being deposited in the surrounding area.&#160; Conventional gas-phase deposition algorithms may not explain observed deposition rates; absorptive partitioning to landscape surfaces is presented as a possible alternative pathway for deposition.</p>
Dear Reviewer, We are very thankful for your great comments. We believe that we have addressed all of the concerns. Please find the attached supplement: the revised sentences and sections in the supplement are highlighted with yellow color.Yours Sincerely, Roghayeh Ghahremaninezhad,
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