When waves meet the shore
Jian Wang, Shengqian Zhou look closely at sea spray aerosols from shoreline wave breaking and associated environmental implications
About 71% of Earth’s surface is covered by the vast oceans. When winds blow over the sea surface, they transfer energy to the water, creating waves. Some of these waves, under the force of strong winds, break and produce tiny airborne droplets that become sea spray aerosols. This process happens across all oceans and is one of the world’s largest sources of aerosols. Despite decades of research, scientists still do not fully understand its impact on the planet’s climate, especially how much it contributes to particles that form clouds, known as cloud condensation nuclei.
Compared with the open oceans, the shallow waters along shorelines cover only a tiny fraction of the sea surface. However, many observation stations for marine aerosols are located near shorelines, and their measurements are often used to study aerosols over open oceans. This raises an important question: Do nearshore sea spray aerosols really reflect what happens in open oceans, in terms of how they form, how high their concentrations are, and how much they contribute to cloud condensation nuclei?
An international team of researchers led by Jian Wang, professor of energy, environmental & chemical engineering in the McKelvey School of Engineering at Washington University in St. Louis, found that strong wave breaking along the shore, particularly during high wave periods, can produce large amounts of sea spray aerosols, significantly increasing both the number of cloud condensation nuclei and the mass of airborne particles in coastal regions. The aerosol generation process at the shoreline is fundamentally different from that in the open oceans. As a result, using coastal aerosol measurements to estimate sea spray aerosols in the open oceans can lead to gross overestimations.
Results from the research were published Aug. 27, 2025, in Science Advances.
Wang and his team, including Shengqian Zhou, a postdoctoral researcher in Wang’s lab and first author of the paper, also found that swell waves — long-traveling waves that form far away from the coast and are not directly linked to local wind — often dominate wave energy in coastal regions. Because wave energy, not local wind speed, controls sea spray production near shorelines, the concentration of sea spray aerosols near shorelines often shows little correlation with wind speed. This is against the common assumption that wind speed can be used to estimate sea spray aerosol emissions.
“Storms over the open oceans generate wind waves,” Zhou said. “After the storm passes, these waves will be transformed into swell waves and can keep traveling for thousands of kilometers. When they eventually reach the shore region, even on calm, windless days, they can break due to friction with the seafloor or by crashing directly against shorelines, which releases part of their energy into the atmosphere in the form of sea spray.”
Their data showed that the contribution of sea spray aerosols to cloud condensation nuclei and aerosol mass concentration can increase by more than three times and exceed 10 micrograms per cubic meter. These effects are widespread, because a large fraction of coastlines around the world regularly experience strong waves. An analysis of wave statistics near 12 coastal atmospheric observatories, ranging from the North Atlantic to Australia, found that high-wave periods occur during more than half the time in some seasons at several stations, and swell waves play dominant roles.
“We knew that this shoreline wave breaking generates sea spray aerosols, but many researchers focused on particles larger than 1 micrometer, which can dominate the mass concentration but few in number,” Wang said. “Our study shows that this shoreline wave breaking generates numerous small particles that make a large contribution to the coastal cloud condensation nuclei. This means that many previous studies using coastal measurements to study sea spray aerosols over open oceans likely overestimated their contributions to cloud condensation nuclei and thus the effects on clouds and climate.”
In addition, nearshore sea spray may also have substantial environmental impacts in the coastal regions. When the waves are high, the particulate matter (PM) mass concentration increases, and that is an important consideration for air quality.
While the sea salt itself may not be harmful, Zhou said, the pollutants in the sea water, such as biogenic toxins, harmful algae and other anthropogenic pollutants, are emitted into the atmosphere by the sea spray and subsequently inhaled by humans. This may strongly affect public health, especially in coastal regions with high waves, polluted seawater and dense populations.
“Existing regional models do not include shoreline aerosol production, or they calculate it incorrectly by relying on local wind speed,” Zhou added. “This makes it difficult for models to accurately capture the real abundance and variations of sea spray aerosols on coastal environment. A deeper understanding of this aerosol production process is needed to better assess and predict the potential environmental and health impacts on communities along coastlines.”
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.
Funding for this research was provided by Office of Biological and Environmental Research of the U.S. Department of Energy Atmospheric System Research Program (DE-SC0021017, DE-SC0021985); Swedish Research Council (Vetenskapsrådet) (2020-05025); Scientific and technical cooperation project between Los Alamos National Laboratory and the University of the Azores (548320 ENA/ARM); and the McDonnell Academy Global Incubator Seed Grant from Washington University in St. Louis.
