Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

Abstract

Abstract. Fine particulate matter plays a central role in the adverse health effects of air pollution. Inhalation and deposition of aerosol particles in the respiratory tract can lead to the release of reactive oxygen species (ROS), which may cause oxidative stress. In this study, we have detected and quantified a wide range of particle-associated radicals using electron paramagnetic resonance (EPR) spectroscopy. Ambient particle samples were collected using a cascade impactor at a semi-urban site in central Europe, Mainz, Germany, in May-June 2015. Concentrations of environmentally persistent free radicals (EPFR), most likely semiquinone radicals, were found to be in the range of (1-7) × 10 11 spins µg −1 for particles in the accumulation mode, whereas coarse particles with a diameter larger than 1 µm did not contain substantial amounts of EPFR. Using a spin trapping technique followed by deconvolution of EPR spectra, we have also characterized and quantified ROS, including OH, superoxide (O − 2 ) and carbon-and oxygen-centered organic radicals, which were formed upon extraction of the particle samples in water. Total ROS amounts of (0.1-3) ×10 11 spins µg −1 were released by submicron particle samples and the relative contributions of OH, O − 2 , C-centered and O-centered organic radicals were ∼ 11-31, ∼ 2-8, ∼ 41-72 and ∼ 0-25 %, respectively, depending on particle sizes. OH was the dominant species for coarse particles. Based on comparisons of the EPR spectra of ambient particulate matter with those of mixtures of organic hydroperoxides, quinones and iron ions followed by chemical analysis using liquid chromatography mass spectrometry (LC-MS), we suggest that the particle-associated ROS were formed by decomposition of organic hydroperoxides interacting with transition metal ions and quinones contained in atmospheric humic-like substances (HULIS).

Release of free amino acids upon oxidation of peptides and proteins by hydroxyl radicals

“…Also, the electron transfer between sites resulting in secondary fragmentation or rearrangement [14, 44], should be considered for the formation of nitrogen-centered radicals. Further verification of the generation of nitrogen-centered radicals and the investigation of their role for the release of amino acids via protein/peptide oxidation by hydroxyl radicals could be obtained by techniques such as electron paramagnetic resonance (EPR) spectroscopy in follow-up studies [45, 46]. …”

Insights into the O : C-dependent mechanisms controlling the evaporation of <i>α</i>-pinene secondary organic aerosol particles

“…in global modelling (e.g. Bergström et al, 2012;. More comprehensive schemes have since been developed linking volatility with other properties, e.g.…”

Size-resolved exposure risk of persistent free radicals (PFRs) in atmospheric aerosols and their potential sources

“…In another study, we have shown that dust particles contain large amounts of EPFRs and that they can be transported over long distances (Chen et al, 2018b). EPFRs in fine particles may be mainly derived from the combustion process, such as traffic sources, which are considered to be an important source of EPFRs in atmospheric PM (Secrest et al, 2016;Chen et al, 2019b The g-factor is a parameter used to distinguish the type of EPFR (Shaltout et al, 2015;Arangio et al, 2016). The g-factor of carbon-centered persistent free radicals is generally less than 2.003, the g factor of oxygen-centered persistent radicals is generally greater than 2.004, and the g factor of carbon-centered radicals with adjacent oxygen atoms is between 2.003 and 2.004 (Cruz et al, 2012).…”