Role of Sea Surface Microlayer Properties in Cloud Formation

Abstract

To date, the relative contribution of primary marine organic matter to the subset of atmospheric particles that nucleate cloud droplets is highly uncertain. Here, cloud condensation nuclei (CCN) measurements were conducted on aerosolized sea surface microlayer (SML) samples collected from the North Atlantic Ocean during the NASA North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), κ values were predicted for three representative high molecular weight (HMW) organic components of marine aerosol: 6-glucose, humic acid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The predicted κ values for pure organic aerosols varied by only ±0.01 across all of the organics chosen. For the desalted SML samples, calculations assuming an organic composition of entirely RuBisCO provided the closest predicted κ values for the desalted SML samples with a mean κ value of 0.53 ± 0.10. These results indicate that it is the sea salt in the SML which drives the cloud formation potential of marine aerosols. While the presence of organic material from the ocean surface waters may increase aerosol mass due to enrichment processes, cloud formation potential of mixed organic/salt primary marine aerosols will be slightly weakened or unchanged compared to sea spray aerosol.

Emerging investigator series: surfactants, films, and coatings on atmospheric aerosol particles: a review

“…Similarly, Cravigan et al 238 were unable to find a significant correlation between organic content and water uptake for SSA generated from seawater from the Southern Ocean during a phytoplankton bloom. Hendrickson et al 239 actually posit that the salts, not the organics, control κ in SSA.…”

Ocean Aerobiology

“…Some studies have shown that primary marine aerosol enriched in organic matter has increased CCN activity (Meskhidze et al, 2011;Ovadnevaite et al, 2011), while other work showed that organic matter reduces CCN activity (Fuentes et al, 2011) or has little to no effect on CCN activation (Deng et al, 2014;Schwier et al, 2015;Collins et al, 2016;Bates et al, 2020;Hendrickson et al, 2021). Sea salt is a major source of CCN in remote marine regions (O'Dowd et al, 1997;Clarke et al, 2006).…”

“…Sea salt is a major source of CCN in remote marine regions (O'Dowd et al, 1997;Clarke et al, 2006). Due to the large emission of sea salt to the atmosphere (2,000-10,000 Tg yr −1 ) and small contribution of organic matter (10 ± 5 Tg yr −1 ) (Gantt and Meskhidze, 2013), organics likely have a small or negligible effect on CCN activity, especially in SSA particles that are a mixture of sea salt and organic matter, as there is simply not enough organic matter to affect CCN properties (Hendrickson et al, 2021) (see Supplementary Table 1). In addition, it is challenging to establish links between ecosystems and CCN due to the complexity and different timescales of processes in both ocean and atmosphere.…”

“…Secondly, we will review the significance of marine aerosol to ecosystem processes and structure, considering the transport and viability of marine microorganisms in the atmosphere, their biogeographical relevance, and potential to influence marine ecosystem processes and biogeochemistry. Finally, we will review the role of marine biogenic aerosols in weather and climate (DeMott et al, 2016;Brooks and Thornton, 2018;Croft et al, 2021), particularly the role of marine primary aerosol in the natural seeding of clouds (Wilbourn et al, 2020;Hendrickson et al, 2021;Zheng et al, 2021). We will synthesize existing knowledge and suggest future research directions to gain a better understanding of the sources, fate, and significance of marine organic aerosol.…”

Phytoplankton Impact on Marine Cloud Microphysical Properties Over the Northeast Atlantic Ocean

“…Such influence was evident in the summer when biological activity is maximized (Gantt et al., 2012 ). On the contrary, some studies lessened the relative importance of the sea‐spray organic fraction in determining its CCN properties (Hendrickson et al., 2021 ), suggesting that non‐sea‐salt sulfate may be the strongest link between marine biology and CCN (Quinn et al., 2019 ; Saliba et al., 2020 ; Sanchez et al., 2018 ).…”