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

Andrea M. Arangio, Haijie Tong, Joanna Socorro, Ulrich Pöschl, Manabu Shiraiwa
2016 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> 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
more » ... ng 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)<span class="thinspace"></span> × 10<sup>11</sup> spins<span class="thinspace"></span>µg<sup>−1</sup> for particles in the accumulation mode, whereas coarse particles with a diameter larger than 1<span class="thinspace"></span>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<sub>2</sub><sup>−</sup>) 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)<span class="thinspace"></span> × 10<sup>11</sup> spins<span class="thinspace"></span>µg<sup>−1</sup> were released by submicron particle samples and the relative contributions of OH, O<sub>2</sub><sup>−</sup>, C-centered and O-centered organic radicals were ∼ <span class="thinspace"></span>11–31, ∼ <span class="thinspace"></span>2–8, ∼ <span class="thinspace"></span>41–72 and ∼ <span class="thinspace"></span>0–25<span class="thinspace"></span>%, 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).</p>
doi:10.5194/acp-16-13105-2016 fatcat:gerlnb2lobcgdaqun22rjuzb6e