Levels, spatial distribution, and source identification of airborne environmentally persistent free radicals from tree leaves

Chen Wang, Yanpeng Huang, Zuotai Zhang*, Zongwei CAI

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

18 Citations (Scopus)


Environmentally persistent free radicals (EPFRs) are receiving increasing concern due to their toxicity and ubiquity in the environment. To avoid restrictions imposed when using a high-volume active sampler, this study uses tree leaves to act as passive samplers to investigate the spatial distribution characteristics and sources of airborne EPFRs. Tree leaf samples were collected from 120 sites in five areas around China (each approximately 4 km × 4 km). EPFR concentrations in particles (<2 μm) on the surface of 110 leaf samples were detected, ranging from 7.5 × 1016 to 4.5 × 1019 spins/g. For the 10 N.D. samples, they were all collected from areas inaccessible by vehicles. The g-values of EPFRs on 68% leaf samples were larger than 2.004, suggesting the electron localized on the oxygen atom, and they were consistent with the road dust sample (g-value: 2.0042). Significant positive correlation was found between concentrations of elemental carbon (tracer of vehicle emissions) and EPFRs. Spatial distribution mapping showed that EPFR levels in various land uses differed noticeably. Although previous work has linked atmospheric EPFRs to waste incineration, the evidence in this study suggests that vehicle emissions, especially from heavy-duty vehicles, are the main sources. While waste incinerators with low emissions or effective dust-control devices might not be an important EPFR contributor. According to our estimation, over 90% of the EPFRs deposited on tree leaves might be attributed to automotive exhaust emissions, as a synergistic effect of primary exhausts and degradation of aromatic compounds in road dust. With adding the trapping agent into the particle samples (<2 μm), signals of hydroxyl radicals were observed. This indicates that EPFRs collected from this phytosampling method can lead to the release of reactive oxygen species (ROS) once they are inhaled by human beings. Thus, this study helps highlight EPFR “hotspots” for potential health risk identification. The spatial distribution mapping shows that the airborne EPFR levels in high traffic-volume areas are higher and vehicle emissions are identified as the dominant contributor of airborne EPFRs.

Original languageEnglish
Article number113353
JournalEnvironmental Pollution
Publication statusPublished - Feb 2020

Scopus Subject Areas

  • Toxicology
  • Pollution
  • Health, Toxicology and Mutagenesis

User-Defined Keywords

  • Environmentally persistent free radicals
  • Passive phytosampling
  • Source identification
  • Spatial distribution pattern
  • Vehicle emissions


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