Factors That Modulate Properties of Primary Marine Aerosol Generated From Ambient Seawater on Ships at Sea

Abstract

Model primary marine aerosol (mPMA) was produced by bubbling clean air through flowing natural seawater in a high‐capacity generator deployed on ships in the eastern North Pacific and western North Atlantic Oceans. Physicochemical properties of seawater and mPMA were quantified to characterize factors that modulated production. Differences in surfactant organic matter (OM) and associated properties including surface tension sustained plumes with smaller bubble sizes, slower rise velocities, larger void fractions, and older surface ages in biologically productive relative to oligotrophic seawater. Production efficiencies for mPMA number (PEnum) and mass (PEmass) per unit air detrained from biologically productive seawater during daytime were greater and mass median diameters smaller than those in the same seawater at night and in oligotrophic seawater during day and night. PEmass decreased with increasing air detrainment rate suggesting that surface bubble rafts suppressed emission of jet droplets and associated mPMA mass. Relative to bubbles emitted at 60 cm depth, PEnum for bubbles emitted from 100 cm depth was approximately 2 times greater. mPMA OM enrichment factors (EFs) and mass fractions based on a coarse frit, fine frits, and a seawater jet exhibited similar size‐dependent variability over a wide range in chlorophyll a concentrations. Results indicate that the physical production of PMA number and mass from the ocean surface varies systematically as interrelated functions of seawater type and, in biologically productive waters, time of day; bubble injection rate, depth, size, and surface age; and physical characteristics of the air‐water interface whereas size‐resolved OM EFs and mass fractions are relatively invariant.

Status and future of numerical atmospheric aerosol prediction with a focus on data requirements

“…This result is consistent with a number of laboratory studies which show an increase in coarse-mode aerosol production with increasing water temperature (e.g., Woolf et al, 1987;Mårtensson et al, 2003;Sellegri et al, 2006;Salter et al, 2014a). Indeed, there appears to be a number of physical and biological effects that can strongly perturb the bubbleaerosol production relationship (Keene et al, 2017). Extensive in situ measurement of aerosol particles within the marine atmospheric boundary layer is unlikely to be viable.…”

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

“…mPMA production was previously characterized at the same hydrographic stations on Georges Bank (S‐1) and in the Sargasso Sea north of Bermuda (S‐3) as part of the Western Atlantic Climate Study (WACS) in August 2012 (Keene et al, ; Long, Keene, Kieber, et al, ; Table S2). During WACS, mPMA were emitted via the detrainment of bubble plumes produced in a high‐capacity generator similar in design and operation to that deployed in this study but configured with coarse (145 to 174 μm pore size) and fine (10 to 20 μm pore size) porosity sintered glass frits (Keene et al, ; Long, Keene, Kieber, et al, ) rather than forced‐air Venturis. Evaluation of results for the two campaigns, although not directly comparable, nonetheless yielded insights regarding influences of bubble plume properties on mPMA production.…”

“…The authors speculate that these differences are driven primarily by corresponding differences in size distributions of subsurface bubbles produced by these methods. However, a subsequent study reported minimal differences in number size distributions of mPMA produced from natural seawater by the detrainment of bubble plumes at similar air entrainment rates and mean depths but with significantly different bubble size distributions (Keene et al, ). The latter results suggest that the size distributions of subsurface bubbles may be less important in modulating the normalized size distributions of PMA than suggested in previous reports.…”

“…The latter results suggest that the size distributions of subsurface bubbles may be less important in modulating the normalized size distributions of PMA than suggested in previous reports. One factor that may contribute to these differences is the presence of bubble rafts at the ocean surface (Keene et al, ). Bubbles associated with detraining plumes from seawater typically coalesce at the interface into larger bubbles that conjoin into raft structures or “white caps.” Bubble rafts can suppress the production of jet droplets associated with bursting bubbles.…”

Status and future of Numerical Atmospheric Aerosol Prediction with a focus on data requirements

“…Most models, however, use simple source functions formulated in terms of wind speed only; the most widely used is that of Monahan et al (1986), which is often applied well beyond the range of conditions from which it was derived and for which it is valid (Spada et al,645 2013). Indeed, there appears to be a number of physical and biological effects that can strongly perturb the bubble/aerosol production relationship (Keene et al, 2017).…”