Atmospheric Chemistry of Organic Peroxy Compounds

Organic peroxy compounds, often denoted RO2, arise from the oxidation of volatile organic compounds (VOCs) by primary atmospheric radicals such as hydroxyl (OH), nitrate (NO3) or ozone (O3). They occupy a central position in tropospheric chemistry, acting both as intermediates in chain propagation and termination reactions and as precursors to secondary organic aerosol (SOA) and ozone. Unimolecular processes such as hydrogen-shift isomerisations compete with bimolecular attacks by NO, NO2 and other peroxy radicals, determining product distributions that influence radical recycling, nitrogen oxide (NOx) budgets and organic aerosol yields. The balance of pathways varies with ambient conditions—particularly NOx levels, temperature and humidity—so that RO2 chemistry exerts global control on oxidant concentrations, air quality and particle formation. Recent advances in laboratory detection and high-level modelling have begun to resolve the multifaceted roles of highly oxidised molecules (HOMs) derived from peroxy radicals in new particle formation and growth, underscoring their significance for climate forcing and human health.

Research from Nature Portfolio

Recent work has elucidated the detailed mechanism of isoprene oxidation initiated by OH radicals, revealing two principal channels for RO2 transformation: reaction with NO and intramolecular hydrogen-shift isomerisation. Both pathways give rise to highly oxidised RO2 species bearing multiple functional groups, which rapidly form stable, closed-shell HOMs. Experimental detection of C5H9O8 and C5H9O9 radicals has demonstrated their dominant role in nucleation and early growth of secondary organic aerosol under both low- and high-NOx conditions. Global modelling indicates that isoprene-derived HOM production rivals that of α-pinene, suggesting a major contribution of biogenic hydrocarbons to particle number concentrations and climate-relevant aerosol loading.

Atmospheric Chemistry of Organic Peroxy Compounds publication trend

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

Technical terms

Organic peroxy radical (RO2): A reactive radical containing an –OO group formed during VOC oxidation in the atmosphere.

Secondary organic aerosol (SOA): Particulate matter generated through gas-to-particle conversion of oxidised volatile organics.

Hydroxyl radical (OH): A highly reactive radical that initiates most daytime oxidation of VOCs.

Hydroperoxide (ROOH): A closed-shell organic peroxide formed by RO2 + HO2 reactions or radical termination.

Highly oxidised molecule (HOM): An extremely low-volatility organic compound containing multiple oxy functional groups, key for new particle formation.

Isomerisation: Intramolecular hydrogen or functional-group shift in RO2 that leads to distinct radical structures and products.

References

1. Highly oxidized products from the atmospheric reaction of hydroxyl radicals with isoprene. Nature Communications (2025).
2. Strong Uptake of Gas-Phase Organic Peroxy Radicals (ROO•) by Solid Surfaces Driven by Redox Reactions. JACS Au (2024).
3. Direct mitigation of secondary organic aerosol particulate pollutants by multiphase photocatalysis. The Science of The Total Environment (2024).
4. Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction. Atmospheric Chemistry and Physics (2019).