Influence of redox-active components and particle size on reactive oxygen species production and oxidative potential of marine aerosols around the Arabian Peninsula

Abstract

Oxidative potential (OP) is a metric for assessing the potential toxicity of ambient particulate matter (PM). However, it is unclear how the OP of PM relates to the presence of redox-active components, the particle size, or their ability to produce reactive oxygen species (ROS) in aqueous solution. For size-segregated marine PM samples collected during a ship cruise around the Arabian Peninsula, we determined the OP of PM using acellular assays, i.e., dithiothreitol (DTT) depletion and H₂O₂ formation assays. The content of environmentally persistent free radicals (EPFRs) as well as the production of radicals upon dissolution of the PM in water were determined by electron paramagnetic resonance spectroscopy. Generally, sub-micrometer particles contributed more strongly to the particle mass-normalized OP (DTT_m, in units of pmol min⁻¹ µg⁻¹), whereas the production of radicals upon dissolution in water was higher in coarse particles. PM_0.49 (i.e., PM with diameter < 0.49 µm) sampled in the Northern Red Sea showed the highest OP out of all samples. The range of DTT_m is lower than previously observed on both land and sea. The OP assays (DTT, H₂O₂) showed positive correlation with concentrations of both water-soluble transition metals (WSTMs) and water-soluble organic carbon (WSOC), while EPFR content and radical production upon dissolution were significantly correlated with WSTMs only. Overall, the OPs of the marine PM samples investigated in this study were substantial, but below levels reported previously from continental or urban sites.