Use of EPR in Monitoring the Effects of Air Pollution

Outdoor air pollution is a major environmental hazard which is detrimental to the health of people globally. The correlation between a number of adverse health effects and the inhalation of ambient particulate matter (PM) is extensively documented by toxicological and epidemiological reports:

  • Long-lived radicals are also part of ambient PM, they are known as environmentally persistent free radicals (EPFRs). They are usually oxygen-centered semiquinone or carbon centered PAH radicals that promote the production of ROS. Their half-life ranges from a few days to a number months and on the internal surface of fine particles, they can even live indefinitely.
  • Reactive nitrogen and oxygen radical species (RNS and ROS) are generated from redox cycling quinoids and polycyclic aromatic hydrocarbons (PAHs) which make up PM. These short-lived toxic radicals have massive potential for harmful oxidative results in pulmonary tissue.
  • Transition metals (V, Co, Mo, Fe, W, Cu, Mn, Cr) are recognized as critical PM components triggering hydroxyl radical (OH) production via Fenton-like reactions. This illustrates that the oxidative potential of PM is a crucial health-relevant metric.

The only method for the non-invasive and direct identification of free radicals and transition metals is Electron Paramagnetic Resonance (EPR) spectroscopy. It is possible to identify, quantify and monitor intrinsic generation of long-lived (EPFRs) and short-lived (ROS and RNS) radicals from ambient particulate matter by studying an EPR signal. EPR can detect traces of transition metals down to parts per billion levels.


Detecting and monitoring production of free radicals from ambient particulate matter and establishing their oxidative potential crucial because of its adverse effects on human health.


The Bruker EMXnano benchtop EPR spectrometer package:

  • Detects, identifies, and quantifies PAHs, ROS, EPFRs, and transition metals which are part of the particulate matter chemistry
  • Establishes the oxidative potential of PM which is a crucial metric to approximate potential adverse effects
  • Monitors radical reactions for better knowledge of the oxidation mechanisms and to establish the half-life of the radicals

Key Features of EMXnano

  • Simple to use
  • Video how-to-guide and startup kit
  • Superior sensitivity
  • Compact footprint
  • No prior EPR experience needed
  • Full workflow for measuring, analyzing and quantifying free radicals and transition metals
  • Accurate results
  • Low cost of ownership

EPR Analysis of PM from Various Air Pollution Sources

  • EPFRs are identified as O-centered semiquinone or C-centered PAH radicals depending on the EPR spectrum characteristics (g-factor).
  • EPR identifies and quantifies long-lived radicals, known as environmentally persistent free radicals (EPFRs).

EPR Study on Airborne PM in Beijing During Haze Events

  • EPFRs are mainly persistent in the PM fraction of dae < 1 μm which are the most hazardous, as shown by EPR.
  • EPR detects EPFRs which are identified as semiquinone radicals in PM with different particle size.
  • The daily monitoring of the EPFRs (spins/g) shows changes in the environment which have long-term effects on human health.
  • This monitoring can be utilized to enact counter measures to decrease health risks to the public.

Analysis of Radical Content in PM

Mineral Dust and Secondary Organic Aerosols (SOA) Make Up a Huge Part of Atmospheric PM

  • EPR identifies, monitors, and quantifies different types of radicals which lead to oxidative stress to lung tissues and cells.
  • In aqueous mixtures of SOA and mineral dust, EPR detects toxic oxygen- and carbon-centered radical species.
  • The radical formation is because of the decomposition of organic hydroperoxides (ROOH) via homolytic cleavage or Fenton-like reactions:
    ROOH → RO + OH
    ROOH + Fe2+ → RO + -OH + Fe3+
    ROOH + Fe2+ → RO- + OH + Fe3+


Due to the adverse health effects of PM, detection, characterization, and monitoring of the free radical chemistry is mandatory and critical. The EMXnano is the solution to investigate and assess this crucial chemistry. EPR can help to gather insight into the mechanisms producing significant amounts of toxic radicals from inhalable ambient particulate matter.

Further Reading

  1. Tong H. et al., Reactive oxygen species formed in aqueous mixtures of secondary organic aerosols and mineral dust influencing cloud chemistry and public health in the Anthropocene, Faraday Discuss. (2017) 200 251
  2. Yang L. et al., Highly elevated levels and particle-size distributions of environmentally persistent free radicals in haze-associated atmosphere, Environ. Sci. Technol. (2017) 51 7936
  3. Borrowman C.K. et al., Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds, Phys. Chem. Chem. Phys. (2016) 18 205
  4. Hellack B. et al., Oxidative potential of particulate matter at a German motorway, Environ. Sci.: Processes Impacts (2015) 17 868
  5. Yang A. et al., Spatial variation and land use regression modeling of the oxidative potential of fine particles, Environ. Health Perspect. (2015) 123 1187

About Bruker BioSpin - NMR, EPR and Imaging

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Last updated: Mar 11, 2022 at 1:34 AM


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