Forest-influenced particles produced more reactive oxygen per unit mass
Urban particles generated more reactive oxygen overall when pollution levels were high, but forest-influenced particles were more reactive relative to their mass.
Editorial illustration — not from the study.
Researchers analyzed fine-particle samples from four Chinese megacities, a German semi-urban site and a boreal forest, along with laboratory-made particles formed from several chemical precursors. They combined ultrahigh-resolution mass spectrometry with measurements of hydrogen peroxide and other reactive species.
The study found that particle composition, rather than particle mass alone, governed the particles’ reactive oxygen potential. A higher proportion of oxidized organic compounds relative to unsaturated organic compounds was associated with greater reactive oxygen production per unit mass, especially in remote, biogenic-influenced air.
What the particles produced
The researchers used a maximum carbonyl ratio–Van Krevelen framework to sort molecular formulas in organic aerosol into two broad groups: oxidized organic compounds and unsaturated organic compounds. Across the urban sites, the ratio of these groups was strongly correlated with reactive oxygen production per unit mass, including hydrogen peroxide production.
Mass-normalized reactive oxygen yields varied independently of particle loading. In contrast, reactive oxygen production normalized by air volume increased as fine-particle mass concentration rose, meaning polluted urban environments had greater overall exposure even though their particles were less reactive per unit mass. Remote, biogenic-influenced aerosols had higher proportions of oxidized compounds and higher mass-normalized yields. Laboratory particles made from isoprene and monoterpenes had the highest yields, while particles made from naphthalene had lower yields per mass.
Why particle chemistry matters
The findings indicate that the amount of fine-particle pollution and its molecular composition provide different information about reactive oxygen production. Considering both could improve assessments of the oxidative activity of chemically complex organic aerosol, rather than relying on particle mass alone.
The composition-based ratio also offers a way to estimate reactive oxygen potential from broad molecular measurements without identifying every individual compound. The study links differences between urban and biogenic-influenced aerosols to differences in their organic chemistry, but it does not measure health outcomes directly.
Evidence and caveats
This was a combined field and laboratory study. The researchers analyzed samples from four Chinese megacities, one German semi-urban site and one boreal-forest site, and tested laboratory-generated secondary organic aerosol from several precursors. They measured molecular composition with ultrahigh-resolution mass spectrometry, hydrogen peroxide with a fluorometric method and radicals with electron paramagnetic resonance and a spin-trapping method.
The results describe reactive oxygen formation in particle samples and their aqueous extracts, not effects in people or biological systems. The field sites and sampling campaigns represent selected environments, so the findings may not apply to every aerosol source or location. The provided abstract and excerpts do not give numerical effect sizes or establish that the composition ratio predicts health risks directly.
// Source
Atmospheric chemistry and physics · 2026 · DOI: 10.5194/acp-26-14655-2026
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