Oxidative Chemistry of Secondary Organic Aerosols

Secondary organic aerosols (SOAs) arise when volatile and intermediate-volatility organic vapours undergo atmospheric oxidation, forming low-volatility products that condense onto particles. Central to SOA formation are radical-driven reactions—primarily initiated by hydroxyl (OH) radicals, ozone and nitrate radicals—which functionalise and fragment organic precursors. The balance between functionalisation (which increases particle mass) and fragmentation (which promotes volatilisation) governs SOA yields and chemical composition. Key precursor classes include biogenic terpenes, anthropogenic aromatics and intermediate-volatility organic compounds (IVOCs), the latter often under-represented in emissions inventories yet capable of contributing major fractions of SOA mass. As oxidation proceeds, particle composition evolves: O : C ratios increase, reflecting progressive addition of oxygenated functional groups, while the carbon oxidation state provides a metric of ageing. These chemical transformations alter particle hygroscopicity, optical properties and toxicity, with implications for climate forcing, air quality and human health. Despite advances in flow reactors, smog chambers and field measurements, models continue to underpredict SOA burdens, owing to incomplete characterisation of IVOC sources, multiphase processes and heterogeneous ageing pathways. Improved mechanistic understanding, coupled with detailed chemical speciation, is essential to constrain SOA impacts on radiative balance, cloud formation and respiratory exposure.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Oxidative Chemistry of Secondary Organic Aerosols publication trend

The graph below shows the total number of articles in oxidative chemistry of secondary organic aerosols across all publications each year (not limited to Nature Index journals).

Technical terms

Secondary organic aerosol (SOA): Particulate matter formed when atmospheric oxidation converts organic vapours into low-volatility products that condense onto existing particles.

Volatile organic compounds (VOCs): Organic gases that evaporate readily into the atmosphere and serve as primary precursors to SOA formation.

Intermediate volatility organic compounds (IVOCs): Organic species with volatility between VOCs and semi-volatile compounds that, upon oxidation, yield substantial SOA mass.

Oxidation flow reactor (OFR): Laboratory apparatus that exposes air samples to elevated oxidant concentrations, simulating days to weeks of atmospheric ageing within minutes.

Oxidation state of carbon (OSc): A measure of the average degree of carbon oxidation in organic molecules, used to assess the extent of aerosol ageing.

References

1. Uncovering the dominant contribution of intermediate volatility compounds in secondary organic aerosol formation from biomass-burning emissions. National Science Review (2024).
2. The chemical composition of secondary organic aerosols regulates transcriptomic and metabolomic signaling in an epithelial-endothelial in vitro coculture. Particle and Fibre Toxicology (2024).
3. Deposition of secondary organic aerosol in human lung model: Effect of photochemically aged aerosol on human respiratory system. Ecotoxicology and Environmental Safety (2023).