Oxidant production from source-oriented particulate matter – Part 1: Oxidative potential using the dithiothreitol (DTT) assay

Abstract

Abstract. Recent epidemiological evidence supports the hypothesis that health effects from inhalation of ambient particulate matter (PM) are governed by more than just the mass of PM inhaled. Both specific chemical components and sources have been identified as important contributors to mortality and hospital admissions, even when these end points are unrelated to PM mass. Sources may cause adverse health effects via their ability to produce reactive oxygen species in the body, possibly due to the transition metal content of the PM. Our goal is to quantify the oxidative potential of ambient particle sources collected during two seasons in Fresno, CA, using the dithiothreitol (DTT) assay. We collected PM from different sources or source combinations into different ChemVol (CV) samplers in real time using a novel source-oriented sampling technique based on single-particle mass spectrometry. We segregated the particles from each source-oriented mixture into two size fractions – ultrafine Dp ≤ 0.17 μm) and submicron fine (0.17 μm ≤ Dp ≤ 1.0 μm) – and measured metals and the rate of DTT loss in each PM extract. We find that the mass-normalized oxidative potential of different sources varies by up to a factor of 8 and that submicron fine PM typically has a larger mass-normalized oxidative potential than ultrafine PM from the same source. Vehicular emissions, regional source mix, commute hours, daytime mixed layer, and nighttime inversion sources exhibit the highest mass-normalized oxidative potential. When we apportion DTT activity for total PM sampled to specific chemical compounds, soluble copper accounts for roughly 50% of total air-volume-normalized oxidative potential, soluble manganese accounts for 20%, and other unknown species, likely including quinones and other organics, account for 30%. During nighttime, soluble copper and manganese largely explain the oxidative potential of PM, while daytime has a larger contribution from unknown (likely organic) species.

On the Redox Activity of Urban Aerosol Particles: Implications for Size Distribution and Relationships with Organic Aerosol Components

“…The higher DTT activity of the upper submicron mode compared to the <0.49 µm mode is in agreement to Charrier et al (2015) [47], who found that submicron fine PM (0.17 µm ≤ Dp ≤ 1.0 µm) typically has a larger mass-normalized oxidative potential than UFPs (PM 0.17 ).…”

“…Recently, [51] studying the distribution of water-soluble DTT activity in ten size fractions within the range 0.056-18 µm, found that, at the roadside Apparently, the lowest DTT activity occurred in fraction <0.49 μm implying that the quasi-UFP mode, that accounted for 57% and 53% of the bulk PM mass at the UT and the UB site, respectively ( Figure 2b) are less enriched with water-soluble DTT-active substances than larger particles. The higher DTT activity of the upper submicron mode compared to the <0.49 μm mode is in agreement to Charrier et al (2015) [47], who found that submicron fine PM (0.17 μm ≤ Dp ≤ 1.0 μm) typically has a larger mass-normalized oxidative potential than UFPs (PM0.17).…”

“…Higher wintertime DTT activity has been frequently reported [9,24,26,27,36,53], on the contrary, other studies found higher activity in summer as compared to winter [31,44,47].…”

Relationship between chemical composition and oxidative potential of secondary organic aerosol from polycyclic aromatic hydrocarbons

“…Based on the chemical composition and the assumption that DTT activities of quinones and transition metals are additive, previous studies have attempted to reconstruct the overall OP in ambient particles based on the chemical composition (Charrier and Anastasio, 2012;Charrier et al, 2015). However, addition of a transition-metal chelator did not result in significant changes in the expression of inflammatory biomarkers (Donaldson et al, 2001), suggesting that oxidative activities from different transition metals may not be additive.…”

“…ROS include a variety of oxidants such as superoxide (O q − 2 ), hydroxyl radical ( q OH), and hydrogen peroxide (HOOH), which could either be introduced into human body directly from inhaled PM or generated by targeted cells (Nel et al, 1998;Pöschl and Shiraiwa, 2015;Rhee, 2006;Verma et al, 2015b). The generation of ROS during multiphase in-teractions between air pollutants and the human respiratory tract is closely related to the chemical composition, since the combination of various pollutants may influence chemical reactivity as well as bioavailability of PM while having synergistic or nonlinear influences on its OP (Antiñolo et al, 2015;Charrier et al, 2015;Fang et al, 2015;Shiraiwa et al, 2012;Xiong et al, 2017).…”