Vertical variability of aerosol properties and trace gases over a remote marine region: A case study over Bermuda

Abstract. Remote marine regions comprise a high fraction of Earth’s surface, but in-situ vertically-resolved measurements over these locations remain scarce. Here we use airborne data during 15 vertical spiral soundings (0.15 – 8.5 km) over Bermuda during the NASA Aerosol Cloud meTeorology Interactions over the western ATlantic Experiment (ACTIVATE) to investigate the impact of different source regions on the vertical structure of trace gases, aerosol particles, and meteorological variables over 1000 km offshore of the U.S. East Coast. Results reveal significant differences in vertical profiles of variables between three different air mass source categories (North America, Ocean, Caribbean/North Africa) identified using the HYSPLIT model: (i) the strongest/weakest pollution signature from North America/Ocean category; (ii) North American air has the highest levels of CO, CH₄, submicron particle number concentration, AMS mass, and highest organic mass fraction along with smoke layers in free troposphere (FT); (iii) Ocean air has the highest relative amount of nitrate, non-sea-salt sulfate, and oxalate, which are key acidic species participating in chloride depletion; (iv) pronounced coarse aerosol signature in the FT and reduced aerosol hygroscopicity in air masses from the Caribbean/North Africa associated with dust transport; and (v) considerable vertical heterogeneity for almost all variables examined, including higher O₃ and submicron particle concentrations with altitude, suggestive that the FT is a potential contributor of both constituents in the marine boundary layer. This study highlights the importance of considering air mass source origin and vertical resolution to capture aerosol and trace gas properties over remote marine areas.