Atmospheric Photochemistry at Air-Water Interfaces

The boundary between the atmosphere and aqueous surfaces, such as the ocean’s topmost microlayer or cloud droplets, is a dynamic arena for sunlight-driven chemistry. At these interfaces, direct photolysis and photosensitisation of organic and inorganic constituents lead to the formation of reactive intermediates, including radicals and excited states. Enrichment of surfactants and chromophores at the air–water boundary enhances light absorption and alters reaction pathways compared with bulk phases. Such interfacial photochemistry governs the production of volatile organic compounds, halogen species and precursors to secondary organic aerosol, driving processes that affect air quality, climate forcing and marine biogeochemical cycles. Advances in spectroscopic and theoretical techniques have begun to unravel the ultrafast dynamics and mechanistic details of these reactions, revealing how local molecular environments and solar spectral variations control reaction efficiencies. Understanding these photochemical processes at air–water interfaces is critical for accurate atmospheric modelling and for predicting feedbacks between the marine surface and global climate systems.

Research from Nature Portfolio

Recent studies have deployed ultrafast spectroscopy and computational chemistry to reveal the primary photodynamics of simple organic acids in aqueous environments. Work on pyruvate at water surfaces shows that deep-UV irradiation induces rapid decarboxylation, while near-UV excitation largely returns molecules to the ground state, altering the yield of key radical precursors. Complementary experiments on model fatty acids at organic-coated interfaces demonstrate that UV-driven surfactant photochemistry can release volatile organic compounds, which subsequently nucleate new secondary organic aerosol particles, underscoring the importance of interfacial photoprocesses for aerosol formation in marine regions.

Atmospheric Photochemistry at Air-Water Interfaces publication trend

The graph below shows the total number of articles in atmospheric photochemistry at air-water interfaces across all publications each year (not limited to Nature Index journals).

Technical terms

Photolysis: The absorption of light by a molecule leading to its dissociation or reaction.

Photosensitiser: A substance that absorbs light and transfers energy to other molecules, initiating chemical reactions.

Sea-surface microlayer: The topmost film of the ocean surface, enriched in organic and inorganic components, where air–water interactions occur.

Secondary organic aerosol (SOA): Fine particles formed from the oxidation and condensation of volatile organic compounds in the atmosphere.

Ozonolysis: The reaction of ozone with unsaturated organic compounds, often yielding carbonyl products and radicals.

References

1. Aqueous pyruvate partly dissociates under deep ultraviolet irradiation but is resilient to near ultraviolet excitation. Nature Communications (2024).
2. Fatty Acid Surfactant Photochemistry Results in New Particle Formation. Scientific Reports (2017).
3. Formation of gas-phase carbonyls from heterogeneous oxidation of polyunsaturated fatty acids at the air–water interface and of the sea surface microlayer. Atmospheric Chemistry and Physics (2014).
4. Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals. Atmospheric Chemistry and Physics (2009).
5. Environmental Processing of Lipids Driven by Aqueous Photochemistry of α‑Keto Acids. ACS Central Science (2018).