The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

Abstract

The oceans represent a significant global source of atmospheric aerosols. Sea spray aerosol (SSA) particles comprise sea salts and organic species in varying proportions. In addition to size, the overall composition of SSA particles determines how effectively they can form cloud droplets and ice crystals. Thus, understanding the factors controlling SSA composition is critical to predicting aerosol impacts on clouds and climate. It is often assumed that submicrometer SSAs are mainly formed by film drops produced from bursting bubble-cap films, which become enriched with hydrophobic organic species contained within the sea surface microlayer. In contrast, jet drops formed from the base of bursting bubbles are postulated to mainly produce larger supermicrometer particles from bulk seawater, which comprises largely salts and water-soluble organic species. However, here we demonstrate that jet drops produce up to 43% of total submicrometer SSA number concentrations, and that the fraction of SSA produced by jet drops can be modulated by marine biological activity. We show that the chemical composition, organic volume fraction, and ice nucleating ability of submicrometer particles from jet drops differ from those formed from film drops. Thus, the chemical composition of a substantial fraction of submicrometer particles will not be controlled by the composition of the sea surface microlayer, a major assumption in previous studies. This finding has significant ramifications for understanding the factors controlling the mixing state of submicrometer SSA particles and must be taken into consideration when predicting SSA impacts on clouds and climate.

Aerosolization of Crude Oil‐Dispersant Slicks Due to Bubble Bursting

“…For the small bubbles, the measured flux and size are in good agreement with the predicted values in the 1.7‐ to 6‐μm range, with ∑EF n = 1.27 (Table ). Hence, the assumption of a single jet drop per bubble; that is, ∑EF n ~1 seems reasonable for this size range, in agreement with recent studies (Lee et al, ; Wang et al, ). However, the results for the medium bubble plume (∑EF n = 8.02) do not agree, indicating that more than one droplet is generated by each bubble.…”

“…Then, EF n is the ratio of particle to bubble fluxes. Similar procedures have been used in prior studies involving pure seawater (Wang et al, ). Since the particle compositions are unknown, the density of pure water along with the known particle volume is used to calculate EF m in picograms per bubble.…”

“…Such breakup has been observed for bubbles with diameters ranging from 20 μm to 3.4 mm (Lee et al, ; Wu, ). With a size of about 5% of the bubble diameter, jet droplets are typically larger and fewer in number compared to film droplets (Spiel, ; Veron, ; Wang et al, ; Wu, ). However, a recent study has shown that jetting caused by 10‐ to 100‐μm bubbles can also generate submicron droplets (Wang et al, ).…”

Marine and Terrestrial Organic Ice‐Nucleating Particles in Pristine Marine to Continentally Influenced Northeast Atlantic Air Masses

“…A tendency to overpredict n INPs is consistent with an evaluation of the Wilson et al () approach using measurements of INPs and TOC in nascent laboratory‐generated SSA (McCluskey et al, ). Similarly, experiments have found differing composition and organic volume fractions for jet drops versus film drops, indicating that the composition and ice nucleation ability of sea spray organic matter is not equal to the composition and ice nucleation ability of the SML (Wang et al, ).…”

Variability in Marine Plankton Ecosystems Are Not Observed in Freshly Emitted Sea Spray Aerosol Over the North Atlantic Ocean

“…The number size distributions generated from the two sampling methods were very similar (Figure b) capturing the smaller SSA mode particles. The size distributions generated with Sea Sweep using smaller frits (2 μm) result in smaller modal diameters (Bates et al, ); however, the 200 μm frits produce a size distribution very similar to that generated with MART which presumably captures film and jet droplets (Wang et al, ). Neither Sea Sweep nor MART produce number size distributions that span the full range of that produced in ambient seawater (Figure b).…”