Dicarbonyl products of the OH radical-initiated reactions of naphthalene and the C1- and C2-alkylnaphthalenes

Naphthalene and the C-2- and C-2-alkylnaphthalenes are the most abundant polycyclic aromatic hydrocarbons (PAHs) in urban atmospheres. Their major atmospheric loss process is by gas-phase reaction with hydroxyl (OH) radicals. In this study, we have used in situ direct air sampling atmospheric pressure ionization mass spectrometry (API-MS) as well as gas chromatography-mass spectrometry (GC/MS) techniques to investigate the products of the gas-phase reactions of OH radicals with naphthalene, naphthalene-d(8), 1- and 2-methylnaphthalene (MN), 1- and 2-MN-d(10), 1- and 2-ethylnaphthalene (EN), and the 10 isomeric dimethy1naphthalenes (DMNs). The major reaction products are ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two beta-carbons and associated alkyl groups, and ring-containing compounds that may be epoxides. Phthalic anhydride and alkylsubstituted phthalic anhydrides were observed as second generation products. The position of alkyl-substitution on the naphthalene ring is a key factor determining the ring cleavage site and the isomeric product distribution.