Each month we welcome a guest blog post from one of our funded Scoping Studies. This month we’re pleased to hear from Dr Jamie Kelly, whose study of Persistent Organic Particles will make use of both the Central Laser Facility and the ISIS Muon and Neutron Source.

Persistent Organic Pollutants (POPs) are potent chemicals that have negative impacts on nearly all major organs and systems of the human body, with health end points including cancer, neurotoxicity, cardiotoxicity, low birth weight, and reduced fertility. POPs also account for a major fraction (20-80%) of the toxicity of fine particles (PM2.5)[1-3], which are responsible for ~400,000 premature deaths each year across Europe[4]. POPs are extremely persistent in the environment, so travel long distances to affect the health of current and future generations near and far from source regions, and are also difficult to excrete, so bioaccumulate and biomagnify in living organisms.

In the atmosphere, heterogenous reactions of POPs play a crucial role in determining human exposure to these pollutants. When bound to PM2.5, POPs can undergo heterogeneous reactions, primarily with ozone (O3)[5]. The kinetics and mechanisms for this process control both the removal of emitted PAHs from the atmosphere, and the formation of degradation products, which can be more toxic than parent compounds by several orders of magnitude. However, most of our knowledge on this chemical process is restricted to a single compound – benzo[a]pyrene (BAP).

Figure 1 shows results from our recent study, which highlights the need for greater insights into heterogeneous reactions of POPs, beyond that of just BAP[6]. In that study, we developed and applied a global atmospheric model and health impact assessment model of Polycyclic Aromatic Hydrocarbons (PAHs) mixtures. We revealed that BAP accounts for only 11 % of the human cancer risk of PAHs worldwide, and that the remaining cancer risk came from other emitted compounds (72 %) and the degradation products (17 %).  However, due to a lack of knowledge of heterogeneous reactions, we were only able to capture the atmospheric levels and associated health risk of a small fraction of the potential degradation products.  Furthermore, sensitivity calculations revealed that uncertainties in the heterogeneous reaction kinetics of PAHs can increase the magnitude of human cancer risk from PAHs by up to 76 %.  In this scoping study, we will quantify the kinetics, mechanisms, and degradation products for the heterogeneous reactions of POPs, using multiple complimentary methods across STFC.   Our team includes multiple academic partners, including Jamie Kelly (University College London) and Maxim Zyskin (University of Oxford), and multiple partners from STFC, including Andy Ward (Central Laser Facility), Sanghamitra Mukhopadhyay (ISIS Neutron and Muon Source), and Alin Elena (Scientific Computing Department). In the experiments, our sample of a POP on the surface of a liquid droplet will be exposed to O3 and monitored using spectroscopic techniques in the Central Laser Facility and ISIS Neutron and Muon Source laboratories, and modelled numerically in Scientific Computing. By utilising multiple methods, based on both experimental and numerical, we aim to provide a complete description of this chemical process. Furthermore, if successful, these methods can be applied to many different POP species and reactants.  In addition, these reaction processes will be directly used in numerical air quality models to derive ambient concentrations and lifetime of POPs, and in the development of emission mitigation policies, and human health impact assessments.

Figure 1 – Global human cancer risk of PAHs taken from Kelly et al. (2021). The first panel (A) shows a breakdown of PAH cancer risk associated with BAP, other emitted PAHs, and the N-PAH degradation products. The the second panel (B) shows global human cancer risk from PAH mixtures estimated by Kelly et al. (2021) and previous studies. The final panel (C) shows the distribution in PAH human cancer risk.


  1. Chung, M.Y., et al., Aerosol-borne quinones and reactive oxygen species generation by particulate matter extracts. Environmental Science & Technology, 2006. 40(16): p. 4880-4886.
  2. Charrier, J.G. and C. Anastasio, On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals. Atmospheric Chemistry and Physics, 2012. 12(19): p. 9321-9333.
  3. McWhinney, R.D., S. Zhou, and J.P.D. Abbatt, Naphthalene SOA: redox activity and naphthoquinone gas-particle partitioning. Atmospheric Chemistry and Physics, 2013. 13(19): p. 9731-9744.
  4. Lelieveld, J., et al., Cardiovascular disease burden from ambient air pollution in Europe reassessed using novel hazard ratio functions. European Heart Journal, 2019. 40(20): p. 1590-1596.
  5. Keyte, I.J., R.M. Harrison, and G. Lammel, Chemical reactivity and long-range transport potential of polycyclic aromatic hydrocarbons – a review. Chemical Society Reviews, 2013. 42(24): p. 9333-9391.
  6. Kelly, J.M., et al., Global Cancer Risk From Unregulated Polycyclic Aromatic Hydrocarbons. Geohealth, 2021. 5(9).

Further details of the project and team members are available on their Scoping Study web page.