Marine Aerosol Production via Detrainment of Bubble Plumes Generated in Natural Seawater With a Forced-Air Venturi

During September–October 2016, a marine aerosol generator configured with forced-air Venturis was deployed at two biologically productive and two oligotrophic regions of the western North Atlantic Ocean to investigate factors that modulate primary marine aerosol (PMA) production. The generator produced representative bubble size distributions with Hinze scales (0.32 to 0.95 mm radii) and void fractions (0.011 to 0.019 L_air L_sw ^-1) that overlapped those of plumes produced in the surface ocean by breaking wind waves. Hinze scales and void fractions of bubble plumes varied among seawater hydrographic regions, whereas corresponding peaks and widths of bubble size distributions did not, suggesting that variability in seawater surfactants drove variability in plume dynamics. Peaks in size-resolved number production efficiencies for model PMA (mPMA) emitted via bubble bursting in the generator were within a narrow range (0.059 to 0.069 μm geometric mean diameter) over wide ranges in subsurface bubble characteristics, suggesting that subsurface bubble size distributions were not the primary controlling factors as was suggested by previous work. Total mass production efficiencies for mPMA decreased with increasing air detrainment rates, supporting the hypothesis that surface bubble rafts attenuate mPMA mass production. Total mass and Na⁺ production efficiencies for mPMA from biologically productive seawater were significantly greater than those from oligotrophic seawater. Corresponding mPMA number distributions peaked at smaller sizes during daytime, suggesting that short-lived surfactants of biological and/or photochemical origin modulated diel variability in marine aerosol production.