Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene

Abstract

The current work focuses on the detailed evolution of the chemical composition of both the gas-and aerosolphase constituents produced from the OH-initiated photooxidation of naphthalene under low-and high-NO x conditions. Under high-NO x conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO 2 + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NO x chemistry, ring-retaining compounds appear to dominate the low-NO x gas-phase products owing to the RO 2 + HO 2 pathway. We are able to chemically characterize 53-68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogento-carbon (H/C), and nitrogen-to-carbon (N/C) ratios measured in bulk samples by high-resolution electrospray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as the ratios observed with online high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting that the chemical compositions and oxidation levels found in the chemically-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO 3 ), and other high-molecular-weight (MW) products are not observed in either the low-or high-NO x SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO 3 ), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high-and low-NO x conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high-and low-NO x SOA. We propose that the major gas-and aerosol-phase products observed are generated through the formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chemical similarity between the laboratory SOA and ambient aerosol collected from Birmingham, Alabama (AL) and Pasadena, California (CA) confirm the importance of PAH oxidation in the formation of aerosol within the urban atmosphere.

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

“…Kramer et al (2016) suggested that isoprene-derived hydroxyhydroperoxide (ISOPOOH) is an essential contributor to the OP of isoprene SOA, consistent with the results of bulk peroxide measurements using 4-nitrophenylboronic acid assay (NPBA assay) by Jiang et al (2017). Since peroxides have been proposed to be a major component in NSOA (Kautzman et al, 2010), it is essential to determine whether or not these peroxides can account for the remaining OP contribution (McWhinney et al, 2013).…”

“…After testing for the sensitivities of various peroxides in KI assay (Fig. S4), and following the previous work by Kautzman et al (2010), benzoyl peroxide (Sigma-Aldrich, ≥ 98 %) was chosen to represent peroxides in NSOA and used as standards for mass calibration in this study. All values are reported as mass fraction of peroxides in the total SOA.…”

“…McWhin- ney et al (2013) found three quinones (1,2-naphthoquinone, 1,4-naphthoquinone, and 5-hydroxy-1,4-naphthoquinone) in NSOA could only account 30 ± 5 % for the observed OP of NSOA, and the source of the remaining DTT activity remains unknown. Peroxides, which are the major contributors to the OP of isoprene SOA (Jiang et al, 2017;Lin et al, 2016;Surratt et al, 2010), may also be abundant in NSOA (Kautzman et al, 2010), but their contribution to the OP of NSOA has not been evaluated. In addition, the composition of SOA may evolve upon atmospheric aging.…”

Naphthalene SOA: redox activity and naphthoquinone gas–particle partitioning

“…They may also be produced as secondary products of polycyclic aromatic hydrocarbon (PAH) oxidation. Naphthalene (Bunce et al, 1997;Chan et al, 2009;Kautzman et al, 2010;Lee and Lane, 2009;Sasaki et al, 1997), phenanthrene (Lee and Lane, 2010;Wang et al, 2007), and anthracene (Kwamena et al, 2006) all generate their corresponding quinone species (naphthoquinone, phenanthrenequinone, and anthraquinone, respectively) via reaction with gas-phase oxidants. Formation of these species from PAH precursors in the atmosphere could increase the redox activity of ambient particles during photochemical aging in locations with PAH emission sources.…”

An enhanced procedure for measuring organic acids and methyl esters in PM<sub>2.5</sub>

“…C 2 -C 6 DCAs are mainly secondary, formed in the atmosphere as their anthropogenic and biogenic precursors are oxidized (Kawamura et al, 1996;Claeys et al, 2004; 2.5 and Yasui, 2005). Although some aromatic acids formed from oxidation reactions of volatile and/or semivolatile polycyclic aromatic hydrocarbons (PAHs) have been studied extensively, such as phthalic acid, which is an oxidation product of naphthalene analogues with OH, nitrate radicals, and ozone (Wang et al, 2007), their mechanistic features and other oxidation products (e.g., 2-hydroxybenzoic acid and phthalic anhydride) of PAHs were still poorly characterized (Lee and Lane, 2009;Kautzman et al, 2010). Thus, it is necessary to develop novel analytical methods that can be used to identify possible tracers and help understand the formation mechanisms of secondary organic acid aerosol.…”