The importance of oceanic emissions for modelling Arctic aerosols and clouds

Emissions of primary aerosols and aerosol precursors from the ocean are key for the Arctic climate. Among those, secondary aerosols from oceanic dimethylsulfide (DMS) are a key species for aerosol-radiation and aerosol-cloud interactions. However, the representation of DMS in atmospheric models is challenging, which generates large uncertainties in the Arctic aerosol budget. In this work we evaluate the sensitivity of simulated Arctic aerosols and clouds in the WRF-Chem atmospheric chemistry model, over a complete annual cycle, to (1) the representation of DMS chemistry in the atmosphere and (2) the oceanic DMS concentration product used as boundary condition. For (2), we compare the results obtained using the Lana et al. (2011) global climatology versus dedicated simulations of the Arctic Ocean biogeochemistry with NEMO-CSIB.
        We find that aerosol number concentrations can change by up to more than 100%, including over sea ice, depending on the model configuration, with a greater sensitivity to the chemistry mechanism than to the oceanic DMS product. This change is negative in the summer, which leads to decreased cloud droplet number and increased (decreased, respectively) shortwave (longwave, respectively) radiation at the surface over sea ice. The opposite effect is found in late spring and autumn. Overall, we find that using a more complex chemistry and better description of Arctic Ocean DMS has an impact on the surface energy budget of +4 W/m² on average for the year 2018, both over sea ice and the open ocean. This configuration also performs best compared to observations. Additional experiments evaluating the changes of aerosol number under future oceanic DMS concentrations, potential emissions of DMS through sea ice, and the role of methanesulfonic acid (MSA) nucleation in summertime aerosol number concentration are presented. 
        This work demonstrates the importance of accurately modeling DMS for simulations of the Arctic aerosol budget and climate, and the value-added of forcing atmospheric models with ocean biogeochemistry simulations.