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

Abstract

Abstract. Owing to the complex nature and dynamic behaviors of secondary organic aerosol (SOA), its ability to cause oxidative stress (known as oxidative potential, or OP) and adverse health outcomes remains poorly understood. In this work, we probed the linkages between the chemical composition of SOA and its OP, and investigated impacts from various SOA evolution pathways, including atmospheric oligomerization, heterogeneous oxidation, and mixing with metal. SOA formed from photooxidation of the two most common polycyclic aromatic hydrocarbons (naphthalene and phenanthrene) were studied as model systems. OP was evaluated using the dithiothreitol (DTT) assay. The oligomerrich fraction separated by liquid chromatography dominates DTT activity in both SOA systems (52 ± 10 % for naphthalene SOA (NSOA), and 56 ± 5 % for phenanthrene SOA (PSOA)). Heterogeneous ozonolysis of NSOA was found to enhance its OP, which is consistent with the trend observed in selected individual oxidation products. DTT activities from redox-active organic compounds and metals were found to be not additive. When mixing with highly redox-active metal (Cu), OP of the mixture decreased significantly for 1,2-naphthoquinone (42 ± 7 %), 2,3-dihydroxynaphthalene (35 ± 1 %), NSOA (50 ± 6 %), and PSOA (43 ± 4 %). Evidence from proton nuclear magnetic resonance ( 1 H NMR) spectroscopy illustrates that such OP reduction upon mixing can be ascribed to metal-organic binding interactions. Our results highlight the role of aerosol chemical composition under atmospheric aging processes in determining the OP of SOA, which is needed for more accurate and explicit prediction of the toxicological impacts from particulate matter.

Predominance of Secondary Organic Aerosol to Particle-bound Reactive Oxygen Species Activity in Fine Ambient Aerosol

“…Transition metals and quinones that induce redox cycling and are well measured by the DTT assay do not react or interfere with DCFH when present at typical ambient concentration levels. This was also observed with the DTT assay for SOA (Wang et al, 2018). Thus, we conclude that DCFH measures the capability of particle-borne compounds to act as reactive oxygen species rather than the potential of species to mediate ROS formation (Zhou et al 2018a).…”

“…The most frequently used assay with DTT shows in some cases good associations with oxidized OA and high values in summer while in other studies better relations with biomass burning and traffic PM components as well as high winter values are observed (Fang et al, 2016;Verma et al 2014Verma et al , 2015Bates et al, 2015). The DTT assay is sensitive to a broad range of components, peroxides and redox cycling species like transition metals and quinones but may suffer from negative interferences between metals and quinones (Wang et al, 2018). Thus, a combination of measurements might be needed to better assess relations between PM composition, oxidative potential and possible health effects.…”

Comparison between five acellular oxidative potential measurement assays performed with detailed chemistry on PM<sub>10</sub> samples from the city of Chamonix (France)

“…Since studies have shown a non-linear DTT response to both PM concentrations (Charrier et al, 2016) or from different chemical species added to the assay Wang et al, 2017), for the DTT and AA assays (single compound assay), extractions were achieved for each sample to a final concentration of 10 µg.ml -1 allowing samples inter-comparison as same extractions 5 at constant-mass were used. For extraction procedure, PM samples were extracted in using a Gamble + DPPC solution and vortexed at maximum speed during 2h at 37°C .…”

Predominance of secondary organic aerosol to particle-bound reactive oxygen species activity in fine ambient aerosol

“…Different acellular assays have been explored to characterize the oxidant activity of PM. For instance, the 2 ,7 -dichlorofluorescin (DCFH) and the p-hydroxyphenylacetic acid (POHPAA) assays respond to a range of organic peroxides (Venkatachari and Hopke, 2008;Wang et al, 2011a;King and Weber, 2013;Zhou et al, 2018a;Hasson and Paulson, 2003) and are used to measure particle-bound ROS (PB-ROS). Similarly, the assay with 9,10-bis (phenylethynyl) anthracene nitroxide (BPEA-nit) measures the amount of PB-ROS, including radicals and metals such as Cu + and Fe 2+ , but not the ROS generated from Fenton chemistry (Miljevic et al, 2010;Hedayat et al, 2016).…”