# Nontargeted Analysis Reveals Organic Compounds That Drive Oxidative Potential in Ambient Particulate Matter

## TL;DR

This study identifies organic compounds in air pollution that contribute to oxidative potential, a key factor in health impacts.

## Contribution

The study reveals new organic compounds, including unknown quinones, that drive oxidative potential in particulate matter.

## Key findings

- Key compounds like C9H6O6 and C9H8O4 are linked to oxidative potential from aromatic precursors.
- Phthalic acid and nitrosalicylic acid are identified as contributors to oxidative potential.
- Metal removal showed organic compounds alone can reach up to 4 nmol DTT min–1 m–3 oxidative potential.

## Abstract

Air pollution adversely
affects human health, with studies consistently
linking it to exposure to particulate matter. However, differential
toxicity remains to be established to improve monitoring and mitigation
efforts. This study examines the oxidative potential (OP) of fine
particulate matter using the dithiothreitol (DTT) assay as a proxy
for toxicity. We analyzed 42 ambient particle filter samples from
Frankfurt, Germany, and Beijing, China, focusing on water-soluble
organic compounds. The aqueous extracts were analyzed for metal content
via inductively coupled plasma–mass spectrometry and for organic
compounds through ultrahigh performance liquid chromatography–high-resolution
mass spectrometry. Utilizing a chelating agent to remove metals allowed
separation of the effects of bulk aerosol and organics only. A hierarchical
cluster analysis identified key compounds linked to OP, including
yet unknown quinones, C9H6O6 (an
oxidation product of o-xylene), and C9H8O4 (an oxidation product of trimethylbenzene),
suggesting secondary products from aromatic precursors. We also found
phthalic acid, a tracer for biomass burning and vehicular exhaust,
and nitrosalicylic acid, an OP-enhancing compound. A volume-normalized
OP of up to 4 nmol DTT min–1 m–3 was observed after metal removal, underscoring the importance of
stable organic compounds and isolating metals to understand their
relationship with OP in ambient particulate matter.