Variability and Sources of Tropospheric Aerosols Over the North Atlantic in Fall: A Model Analysis in Support of the NASA NAAMES Earth-Venture Suborbital-2 Mission

Abstract:

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is a five-year Earth-Venture Suborbital-2 Mission to characterize the plankton ecosystems and their influences on remote marine aerosols, boundary layer clouds, and their implications for climate in the North Atlantic, with the first field deployment in November 2015. While marine-sourced aerosols have been shown to make important contributions to surface aerosol loading, cloud condensation nuclei and ice nuclei concentrations over remote marine and coastal regions, it is still a challenge to differentiate the marine biogenic aerosol signal from the strong influence of continental pollution outflow. As a pre-mission analysis, we examine here the spatiotemporal variability and quantify the sources of tropospheric aerosols over the North Atlantic during November 2008 using a state-of-the-art chemical transport model (GEOS-Chem). The model is driven by the Modern-Era Retrospective analysis for Research and Applications (MERRA at 2°×2.5° horizontal resolution) from the NASA Global Modeling Assimilation Office (GMAO). It includes sulfate-nitrate-ammonium aerosol thermodynamics coupled to ozone-NOx-hydrocarbon-aerosol chemistry, mineral dust, sea salt, elemental and organic carbon aerosols, especially a recently implemented parameterization for the marine primary organic aerosol emission. The simulated aerosols over the North Atlantic are evaluated with available satellite (e.g., MODIS) observations of aerosol optical depths (AOD) and surface aerosol measurements. We diagnose transport pathways for continental pollution outflow over the North Atlantic using carbon monoxide, an excellent tracer for anthropogenic pollution transport. Simulations indicate that, along the NAAMES nominal ship and flight tracks (40°W, 40-57°N), episodic pollution transport associated with frontal passages occurs at both the surface and free troposphere, with periods of relatively unperturbed marine air as indicated by simulated sea salt aerosols. We will also conduct model perturbation experiments to quantify the relative contributions of terrestrial and oceanic sources to the aerosol loading, AOD, and their variability over the North Atlantic. These simulations will provide valuable guidance to the NAAMES flight planning.