Size-Dependent Morphology, Composition, Phase State, and Water Uptake of Nascent Submicrometer Sea Spray Aerosols during a Phytoplankton Bloom

Abstract

The impact of sea spray aerosols (SSAs) on Earth's climate remains uncertain in part due to size-dependent particle-to-particle variability in SSA physicochemical properties such as morphology, composition, phase state, and water uptake that can be further modulated by the environment relative humidity (RH). The current study investigates these properties as a function of particle size and RH, while focusing on submicrometer nascent SSA (0.1−0.6 μm) collected throughout a phytoplankton bloom. Filter-based thermal optical analysis, atomic force microscopy (AFM), and AFM photothermal infrared spectroscopy (AFM−PTIR) were utilized in this regard. AFM imaging at 20% RH identified five main SSA morphologies: prism-like, core−shell, rounded, rod, and aggregate. The majority of smaller SSAs throughout a bloom were rounded, while larger SSAs were core−shell. Filter-based measurements revealed an increasing organic mass fraction with decreasing SSA size. The organic matter is shown to primarily reside in a rounded and core−shell SSA, while the prism-like and rod SSA are predominantly inorganic salts (i.e., sodium chloride, nitrates, and sulfates) with relatively low organic content, as determined by AFM−PTIR spectroscopy. AFM phase state measurements at 20% RH revealed an increasing abundance of core−shell SSA with semisolid shells and rounded SSA with a solid phase state, as the particle size decreases. At 60% RH, shells of core−shell and rounded SSA uptake water, become less viscous, and their phase states change into either semisolid or liquid. Collectively, findings reveal the dynamic and size-dependent nature of SSA's morphology, composition, phase states, and water uptake, which should be considered to accurately predict their climate-related effects.

Particle phase-state variability in the North Atlantic free troposphere during summertime is determined by atmospheric transport patterns and sources

“…Among the Pico 2015 samples, carbonaceous particles dominate S1 and S3 to S6 (∼ 62 %, ∼ 63 %, ∼ 80 %, ∼ 52 %, and ∼ 61 %, respectively). Sulfate (CNOS and sea salt with sulfate) particles are also abundant in all samples (∼ 18 % to 34 %), suggesting that these particles were possibly involved in cloud processing (Ervens et al, 2011;Kim et al, 2019;Lee et al, 2011Lee et al, , 2012Zhou et al, 2019). Samples S2 and S5 have high dust contributions (∼ 16 % and ∼ 14 %, respectively) due to air masses from Africa.…”

“…Moreover, Cheng et al (2015), Petters and Kasparoglu (2020), and Kaluarachchi et al (2022) have shown that particle size also affects particle viscosity. This appears to be the case for some samples when comparing the aspect ratio distributions for the Pico 2015 particles collected on stage 3 (left violin plots, 50 % cutoff size is >0.15 µm) with the corresponding distributions for those collected on stage 4 (right violin plots, 50 % cutoff size is >0.05 µm); see Fig.…”

“…Sea salt particles were typically from marine sprays, since air masses were transported over the North Atlantic Ocean. Sea salt with sulfate particles with area-equivalent diameters greater than 0.6 µm have been shown to be a product of aqueous phase processing (i.e., fog and cloud processing) (Ervens et al, 2011;Kim et al, 2019;Lee et al, 2011Lee et al, , 2012Zhou et al, 2019), and those with area-equivalent diameters less than 0.6 µm might have been generated from marine sources (Sorooshian et al, 2007;Yu et al, 2005). Sea salt and sea salt with sulfate particles dominated (∼ 28.2 % and ∼ 31.5 %, respectively) sample S3-1, which had a smaller fraction of organic particles (OC and CNO, ∼ 6.3 % and ∼ 23.4 %, respectively) than those in other samples.…”

Impacts of marine organic emissions on low-level stratiform clouds – a large eddy simulator study

“…Cochran et al (2017) showed that the hygroscopicity of the sea spray aerosol depended on the type of the organic molecules dominant in the sea spray, which varied between different-sized particles. Size dependence of the composition has also been demonstrated by Ault et al (2013), Facchini et al (2008), and Kaluarachchi et al (2022. However, some other recent publications (Bates et al, 2020;Collins et al, 2016;Cravigan et al, 2020) have reported that the hygroscopicity of sea spray aerosol seems to stay largely invariable regardless of the organic fraction, while Ovadnevaite et al (2011) reported a complex behaviour of low hygroscopic growth in aerosol phase combined with high CCN activation efficiency.…”

Number‐Size Distribution and CCN Activity of Atmospheric Aerosols in the Western North Pacific During Spring Pre‐Bloom Period: Influences of Terrestrial and Marine Sources

“…Laboratory and mesocosm experiments based on bubble-bursting have suggested that variations in biological parameters, aerosol, and CCN activity may be caused by differences in the structures of OM components in SSA particles (Cravigan et al, 2020;Freney et al, 2021) and may depend on the phytoplankton species in the community (Wang et al, 2015). Recently, changes in the chemical properties of SSA (phase-state and solubility) were suggested in transitions of the bloom stage (between pre-bloom, bloom, and post-bloom periods) (Kaluarachchi et al, 2022). The response of hygroscopicity/CCN activity to biological activity at different bloom stages remains uncertain, although tank experiment has been conducted (Schwier et al, 2015).…”