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Interdroplet Electrostatic Interactions Contribute to Dark Oxidation in Nighttime Sea Sprays
Yu Xia1,2, Jing Song1, Jinheng Xu2
1Hubei Key Laboratory of Environmental and Health Effects of Persistent Toxic Substances, School of Environment and Health, Jianghan University, Wuhan430056, China.
Environmental Science & Technology
|August 11, 2026
Summary
Nighttime sea spray shows strong oxidation, exceeding seawater levels. Droplet interactions, not single droplets, drive this dark oxidative activity in the marine boundary layer.
Area of Science:
- Atmospheric Chemistry
- Ocean-Atmosphere Interactions
- Marine Aerosol Science
Background:
- Nighttime oxidative processing in the marine boundary layer is poorly understood due to reduced photochemical oxidant sources after sunset.
- Conventional understanding of sea spray oxidation primarily focuses on single-droplet behavior.
Purpose of the Study:
- To investigate the oxidative activity of freshly emitted sea spray under dark conditions.
- To elucidate the mechanisms behind nighttime sea spray oxidation and the role of droplet interactions.
Main Methods:
- Field measurements at three coastal sites in China.
- Controlled laboratory experiments with isolated and interacting sea spray droplets.
- Numerical simulations, high-speed imaging, and photon-emission measurements.
- Flow-controlled chamber experiments.
Main Results:
- Freshly emitted sea spray exhibited significantly enhanced oxidative activity compared to source seawater, even in darkness.
- Oxidation was suppressed in isolated droplets but pronounced in interacting droplet populations, forming hydrogen peroxide and hydroxyl radicals.
- Droplet interactions were linked to localized electrostatic environments promoting oxidant formation and changes in gas-phase oxidants.
- Nighttime field observations correlated elevated wave activity with increased ozone and decreased nitrogen oxides (NOx) and sulfur dioxide (SO2).
Conclusions:
- Sea spray droplet interactions are a critical, previously underappreciated factor in nighttime marine boundary layer oxidation.
- The behavior of real sea sprays cannot be fully explained by single-droplet chemistry alone.
- Droplet interactions contribute significantly to atmospheric oxidant levels during nighttime hours when photochemical production is minimal.
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