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Published January 21, 2010 | Supplemental Material
Journal Article Open

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


The current work focuses on the detailed evolution of the chemical composition of both the gas- and aerosol-phase constituents produced from the OH-initiated photooxidation of naphthalene under low- and high-NOₓ conditions. Under high-NOₓ conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO₂ + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NOₓ chemistry, ring-retaining compounds appear to dominate the low-NOₓ gas-phase products owing to the RO₂ + HO₂ pathway. We are able to chemically characterize 53−68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogen-to-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-OSO₃), and other high-molecular-weight (MW) products are not observed in either the low- or high-NOₓ SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO₃), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high- and low-NOₓ conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high- and low-NOₓ 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.

Additional Information

© 2009 American Chemical Society. Received: September 3, 2009; Revised Manuscript Received: October 15, 2009. Publication Date (Web): November 11, 2009. This research was funded by the Office of Science (BER), US Department of Energy Grant No. DE-FG02-05ER63983, US Environmental Protection Agency STAR Research Assistance Agreement No. RD-83374901 and US National Science Foundation grant ATM-0432377. The Electronic Power Research Institute provided support for the SEARCH network field samples. The GC/TOF and CIMS instruments used in this study were purchased as part of a major research instrumentation grant from the National Science Foundation (ATM-0619783). Assembly and testing of the CIMS instrument was supported by the Davidow Discovery Fund. The Waters UPLC/(-)ESI-TOFMS (LCT Premier XT TOFMS) was purchased in 2006 with a grant from the National Science Foundation, Chemistry Research Instrumentation and Facilities Program (CHE-0541745). We thank J. Stockdill for synthesis of 2-formylcinnamaldehyde. We would also like to thank E. S. Edgerton of Atmospheric Research & Analysis (ARA), Inc., for providing the high-volume filter sampler, as well as providing detailed information on its operation procedures, used in the sampling of fine aerosols during PACO. This publication has not been formally reviewed by the EPA. The views expressed in this document are solely those of the authors and EPA does not endorse any products mentioned in this publication.

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August 19, 2023
October 19, 2023