When Ocean Waves Reach the Shoreline

Across approximately 71% of our planet’s surface, vast oceans stretch uninterrupted, playing a crucial role in Earth’s climate system. These expansive bodies of water interact constantly with the atmosphere above, creating dynamic processes whose complexities scientists are still unraveling. A particularly captivating process involves the generation of sea spray aerosols (SSA), tiny particles created when waves break under the influence of wind. These minuscule droplets not only carry sea salt but serve as vital components in atmospheric chemistry, cloud formation, and possibly climate regulation. However, despite decades of intense scrutiny, the precise influence of these sea spray aerosols on atmospheric processes and climate feedbacks remains ambiguous and challenging to quantify.

Traditionally, research on SSA has often relied heavily on aerosol observations made near shorelines. These coastal regions, while accessible and convenient for monitoring, cover only a small fraction of Earth’s ocean surface compared to the vast open ocean. This reliance on data from nearshore sites carries an implicit assumption: that the particle characteristics, concentrations, and formation mechanisms found at the coast are representative of much broader oceanic environments. But recent research spearheaded by an international collaboration led by Jian Wang, professor at the McKelvey School of Engineering, Washington University in St. Louis, challenges this foundational assumption. Their findings suggest that the production of sea spray aerosols in coastal zones is fundamentally distinct from that in peripheral open ocean waters, potentially skewing our broader understanding of marine aerosol contributions to climate.

Wang and his research team identified a pivotal driver in this coastal aerosol generation: the breaking of strong waves along the shoreline. During periods of elevated wave activity, intense wave breaking produces disproportionately large numbers of sea spray particles. This enhanced aerosol production nearshore markedly elevates both the number concentration of cloud condensation nuclei (CCN)—the tiny particles upon which cloud droplets condense—and the mass of airborne particulate matter. Importantly, this contrasts with SSA generation in open water, where wind speed is conventionally regarded as the primary controlling factor. Thus, the wave-driven aerosol production mechanism specific to shorelines leads to substantial overestimations when coastal aerosol measurements are extrapolated to represent open ocean conditions.

One remarkable aspect of this coastal aerosol generation is the dominance of swell waves. Unlike local wind-driven waves, swell waves originate from distant storms, traveling thousands of kilometers across open ocean basins before reaching coastal regions. These long-period waves, driven by residual energy rather than ongoing local wind stress, influence coastal waters even during calm and windless conditions. Upon approaching shallow nearshore environments, friction with the seafloor and physical interactions with the shoreline cause swell waves to break, liberating sea salt particles into the atmosphere in the form of sea spray. This discovery subverts the prevailing paradigm that links SSA concentration directly to local wind speed, highlighting an alternative and less widely appreciated mechanism of aerosol production.

The implications of this swell-dominated wave breaking are profound. Data from Wang’s study reveal that during high-wave conditions near shore, the concentration of sea spray aerosols contributing to CCN can increase by more than threefold. Additionally, particulate mass concentrations can exceed 10 micrograms per cubic meter in these regions. Given that coastal areas worldwide frequently experience elevated wave conditions, this enhanced aerosol production is not a localized anomaly but a widespread phenomenon. The team’s analysis extended across a wide range of geographical locations—from the North Atlantic to Australia—demonstrating that multiple coastal observatories consistently experience high-wave periods for significant portions of various seasons, with swell waves playing a dominant role in aerosol generation during these intervals.

Previous research often emphasized sea spray particles larger than one micrometer, which contribute significantly to the aerosol mass budget but are comparatively sparse in terms of particle number concentration. However, Wang’s study draws attention to the critical importance of smaller particles produced at the shoreline. These fine particles, though contributing less to total mass, dominate the sheer number of aerosols that function as cloud condensation nuclei. This shift in focus from mass to number concentration reshapes our understanding of cloud formation processes in coastal environments and calls into question the accuracy of prior studies that extrapolated coastal aerosol data to infer global marine aerosol dynamics.

The environmental and public health repercussions of coastal sea spray aerosols are also considerable. Elevated particulate matter levels accompanying strong wave events can degrade air quality along shorelines, posing risks to human health. While sea salt itself is generally benign, the ocean is a reservoir for a diverse array of pollutants, including biogenic toxins, harmful algae constituents, and anthropogenic contaminants. When wave breaking injects these particles into the atmosphere, they become inhalable by coastal populations, potentially exacerbating respiratory and cardiovascular conditions. This intersection of natural oceanic processes with pollution underlines the urgency for holistic assessments of coastal air quality, particularly in densely populated regions with polluted waters and frequent high-wave events.

One striking challenge identified by the researchers concerns the accuracy of existing atmospheric and regional air quality models. Many models currently either omit shoreline aerosol production or incorporate it inaccurately by relying excessively on local wind speeds as proxies for aerosol emission rates. This leads to systematic underestimation or misrepresentation of the abundance and temporal variability of sea spray aerosols near shorelines. The findings advocate for the integration of wave-driven aerosol production mechanisms into modeling frameworks, particularly accounting for the role of swell waves and wave breaking independent of local wind, to enhance predictive accuracy and inform climate and health impact assessments.

The implications of these results extend well beyond coastal zones. Sea spray aerosols serve as important precursors for cloud droplet formation, influencing cloud albedo, lifetime, and precipitation patterns, which in turn feed back into global climate regulation. Mischaracterizing the sources and distributions of these aerosols risks propagating errors through climate models, leading to uncertainties in predictions of radiative forcing and hydrological cycles. With shoreline-produced aerosols differing markedly from open ocean counterparts in size distribution and concentration, reassessing these contributions is vital for refining climate projections.

Furthermore, the study promotes a paradigm shift in the methodologies employed to study marine aerosols. Remote and open ocean measurements are essential, requiring investment in offshore observation platforms and autonomous sensors capable of capturing aerosol characteristics in situ. This would help circumvent biases introduced by coastal sampling and better inform global aerosol budgets. Additionally, combining observational data with advanced wave modeling can elucidate the spatial and temporal variability of aerosol production linked to changing wave regimes under a warming climate, where storm intensity and frequency may evolve.

In conclusion, the work led by Jian Wang and colleagues represents a critical advancement in marine aerosol science, illuminating the complex interplay between physical oceanography and atmospheric chemistry at shorelines. By unveiling how shoreline wave breaking—and not just local winds—dominates sea spray aerosol formation near coasts, their results urge a recalibration of assumptions underpinning climate studies and air quality assessments. This enhanced understanding not only advances fundamental science but also lays the groundwork for improved environmental policies aimed at protecting vulnerable coastal populations.

Subject of Research: Coastal sea spray aerosol production and its implications for climate and air quality

Article Title: Shoreline wave breaking strongly enhances the coastal sea spray aerosol population: climate and air quality implications

News Publication Date: August 27, 2025

Web References: https://doi.org/10.1126/sciadv.adw0343

References:
Zhou S, Salter M, Bertram T, Brito Azevedo E, Reis F, Wang J. Shoreline wave breaking strongly enhances the coastal sea spray aerosol population: climate and air quality implications. Science Advances, Aug. 27, 2025. DOI: https://doi.org/10.1126/sciadv.adw0343

Keywords

Atmospheric aerosols, Chemical modeling, Clouds, Earth systems science

Tags: aerosol particle characteristicsatmospheric chemistry and climateclimate feedback mechanismsclimate regulation by aerosolscoastal aerosol observationsinternational ocean research collaborationmarine aerosol impact on weatherocean surface monitoringocean wave dynamicsocean-atmosphere interactionssea spray aerosol generationshoreline environmental studies