Naphthalene SOA: redox activity and naphthoquinone gas–particle partitioning

Abstract

Abstract. Chamber secondary organic aerosol (SOA) from low-NO x photooxidation of naphthalene by hydroxyl radical was examined with respect to its redox cycling behaviour using the dithiothreitol (DTT) assay. Naphthalene SOA was highly redox-active, consuming DTT at an average rate of 118 ± 14 pmol per minute per µg of SOA material. Measured particle-phase masses of the major previously identified redox active products, 1,2-and 1,4-naphthoquinone, accounted for only 21 ± 3 % of the observed redox cycling activity. The redox-active 5-hydroxy-1,4-naphthoquinone was identified as a new minor product of naphthalene oxidation, and including this species in redox activity predictions increased the predicted DTT reactivity to 30 ± 5 % of observations. These results suggest that there are substantial unidentified redox-active SOA constituents beyond the small quinones that may be important toxic components of these particles. A gas-to-SOA particle partitioning coefficient was calculated to be (7.0 ± 2.5) × 10 −4 m 3 µg −1 for 1,4-naphthoquinone at 25 • C. This value suggests that under typical warm conditions, 1,4-naphthoquinone is unlikely to contribute strongly to redox behaviour of ambient particles, although further work is needed to determine the potential impact under conditions such as low temperatures where partitioning to the particle is more favourable. Also, higher order oxidation products that likely account for a substantial fraction of the redox cycling capability of the naphthalene SOA are likely to partition much more strongly to the particle phase.

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

“…The protocols used in this work are adapted from those of McWhinney et al (2011McWhinney et al ( , 2013. The SOA extracts were first evaporated to complete dryness in a 5.0 L min −1 of N 2 using a blow-off system (N-EVAP, Organomation, USA).…”

“…To date, the DTT assay has been applied in a few studies to evaluate the OP of both laboratory and ambient SOA (McWhinney et al, 2013;Tuet et al, 2017b;Verma et al, 2015a). However, owing to the complex and dynamic property of SOA, there is limited understanding of the relationship between detailed SOA composition and its OP (Charrier and Anastasio, 2012;Pöschl and Shiraiwa, 2015;Tuet et al, 2017b).…”

“…Previous work (Antiñolo et al, 2015;Bolton et al, 2000;Charrier and Anastasio, 2012;Cho et al, 2005;Jiang et al, 2017;Tuet et al, 2017b) indicated that polycyclic aromatic hydrocarbons (PAHs) are unreactive towards DTT while their oxidation products, such as quinones, can be highly redox-active. Quinones can be directly emitted from traffic or formed from secondary oxidation (Cho et al, 2004;McWhinney et al, 2013), and are able to consume antioxidants in a catalytic cycle ( Fig. 1; Bolton et al, 2000;Valavanidis et al, 2005).…”

“…In vitro cellular assays were conducted by detecting biological endpoints of the exposure, including heme oxygenase-1 (HO-1) and other cytokines as well as macrophage-related biomarker expressions (Krapf et al, 2017;Li et al, 2003b). On the other hand, acellular assays use specific chemicals, such as dithiothreitol (DTT), ascorbate (AA), and glutathione (GSH), as surrogates of low molecular weight (MW) antioxidants (Fang et al, 2016;Godri et al, 2011;McWhinney et al, 2013). Among acellular assays, the DTT assay quantifies OP by measuring the DTT depletion rate over a fixed time interval, which mimics the physiological process of electron transfer from biological antioxidants to dissolved O 2 (Cho et al, 2005).…”

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

“…Oxidative stress is mediated by reactive oxygen species (ROS), including OH, H 2 O 2 and superoxide (O − 2 ), as well as organic radicals (Pryor et al, 1995;Winterbourn, 2008;Birben et al, 2012;. Upon PM deposition into the respiratory tract and interactions with lung antioxidants, H 2 O 2 can be generated by redox-active components contained in PM 2.5 such as transition metals (Charrier et al, 2014;Fang et al, 2016), semiquinones (Kumagai et al, 1997;Cho et al, 2005;McWhinney et al, 2013) and humic-like substances (Kumagai et al, 1997;Cho et al, 2005;Lin and Yu, 2011;Charrier et al, 2014;Dou et al, 2015;Fang et al, 2016;Verma et al, 2015a). H 2 O 2 can be converted into highly reactive OH radicals via Fenton-like reactions with iron and copper ions (Charrier et al, 2014;Enami et al, 2014).…”