Editing IPCC:AR6/WGI/Chapter-6 (section)

==== 6.2.2.5 Oceanic Emissions of Marine Aerosols and Precursors ====

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Oceans are a significant source of marine aerosols that influence climate directly by scattering and absorbing solar radiation or indirectly through the formation of cloud condensation nuclei (CCN) and ice nucleating particles (INPs). Marine aerosols consist of primary sea-spray particles and secondary aerosols produced by the oxidation of emitted precursors, such as dimethylsulphide (DMS) and numerous other BVOCs. Sea-spray particles, composed of sea salt and primary organic aerosols (POA), are produced by wind-induced wave breaking as well as the direct mechanical disruption of waves. The understanding of sea-spray emissions has increased substantially over the last five years, however, the knowledge of formation pathways and factors influencing their emissions continue to have large uncertainties ( [[#Forestieri--2018|Forestieri et al., 2018]] ; [[#Saliba--2019|Saliba et al., 2019]] ). The emission rate of sea-spray particles is predominantly controlled by wind speed. Since AR5, the influence of other factors, including sea surface temperature, wave history and salinity is increasingly evident (Callaghan et al. , 2014; Grythe et al. , 2014; Ovadnevaite et al. , 2014; Salter et al. , 2014; Barthel et al. , 2019) . Marine POA, often the dominant submicron component of sea spray, are emitted as a result of oceanic biological activity, however the biological processes by which these particles are produced remain poorly characterized contributing to large uncertainties in global marine POA emissions estimates (Tsigaridis et al. , 2014; Cravigan et al. , 2020; Hodzic et al. , 2020) '''.''' Furthermore, the particle size and chemical composition of sea-spray particles, and how these evolve in response to changing climate factors and dynamic oceanic biology, continue to have large uncertainties.

DMS, the largest natural source of sulphur in the atmosphere, is produced by marine phytoplankton and is transferred from ocean water to the atmosphere due to wind-induced mixing of surface water. DMS oxidizes to produce sulphate aerosols and contributes to the formation of CCN. Since AR5, the range in global DMS flux estimates reduced from 10–40 TgS yr <sup>–1</sup> to 9–34 TgS yr <sup>–1</sup> with a ''very likely'' range of 18–24 TgS yr <sup>–1</sup> based on sea-surface measurements and satellite observations ( [[#Lana--2011|Lana et al., 2011]] ). DMS production, and consequently emissions, have been shown to respond to multiple stressors, including climate warming, eutrophication, and ocean acidification. However, large uncertainties in process-based understanding of the mechanisms controlling DMS emissions, from physiological to ecological, limit our knowledge of past variations and our capacity to project future changes.

Overall, there is ''low confidence'' in the magnitude and changes in marine aerosol emissions in response to shifts in climate and marine ecosystem processes.

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