An Automated Online Field Instrument to Quantify the Oxidative Potential of Aerosol Particles via Ascorbic Acid Oxidation

Abstract

Abstract. Large-scale epidemiological studies have consistently shown that exposure to ambient particulate matter (PM) is responsible for a variety of adverse health effects. However, the specific physical and chemical properties of particles that are responsible for observed health effects, as well as the underlying mechanisms of particle toxicity upon exposure, remain largely uncertain. Studies have widely suggested that the oxidative potential (OP) of aerosol particles is a key metric to quantify particle toxicity. OP is defined as the ability of aerosol particle components to produce reactive oxidative species (ROS) and deplete antioxidants in vivo. Traditional methods for measuring OP using acellular assays largely rely on analyzing PM collected in filters offline. This is labor intensive and involves a substantial time delay between particle collection and OP analysis. It therefore likely underestimates particle OP, because many reactive chemical components which are contributing to OP are short-lived and therefore degrade prior to offline analysis. Thus, new techniques are required to provide a robust and rapid quantification of particle OP, capturing the chemistry of oxidizing and short-lived highly reactive aerosol components and their concentration dynamics in the atmosphere. To address these measurement shortcomings, we developed a portable online instrument that directly samples particles into an ascorbic acid-based assay under physiologically relevant conditions of pH 6.8 and 37 °C, providing continuous accurate OP measurements with a high time resolution (5 mins). The instrument runs autonomously for up to three days and has a detection limit of about 5 µg/m3 in an urban environment, which allows the characterization of particle OP even in low-pollution areas.

Robust quantification of the burst of OH radicals generated by ambient particles in nascent cloud droplets using a direct-to-reagent approach

“…Zhang et al (2022) showed that on average more than 90% of ROS in a photochemically aged mixture of primary combustion soot particles and naphthalene or β-pinene aerosols were short-lived. In addition, Utinger et al (2023) demonstrated the rapid decay of oxidizing components of (-pinene) secondary organic aerosol using a direct-to-reagent approach similar to that used here but with an ascorbic acid based assay, with simultaneous comparison to filter samples analyzed immediately after particle collection. The decay of particle-associated oxidizing species appears to occur in three phases, with one rapid (t 1/2 < 1 min), one medium decay phase (t 1/2 ~20 hrs.)…”

Experimental factors influencing the bioaccessibility and the oxidative potential of transition metals from welding fumes

“…10 Recent studies reported that storage (>7 days) of particles collected on the lter prior to analyses leads to a signicant underestimation of OP. [90][91][92] The soluble Mn concentration decreases with the OP DTT especially when comparing fresh WFs and WFs stored for 35 days in air at 20 °C. The solubility of Mn in the extracts of the tested WF samples plays an important role in the OP DTT measurements.…”