Alkyl Nitrate, Hydroxyalkyl Nitrate, and Hydroxycarbonyl Formation from the NOx−Air Photooxidations of C5−C8 n-Alkanes

Abstract

Products of the gas-phase reactions of OH radicals with the n -alkanes n -pentane through n -octane at 298 ± 2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography−mass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry. The formation yields of alkyl nitrates from n -hexane, n -heptane, and n -octane were measured by GC-FID, with the sum of the isomeric alkyl nitrates being 0.141 ± 0.020, 0.178 ± 0.024, and 0.226 ± 0.032, respectively. These alkyl nitrate yields are ∼35% lower than previous data reported from this laboratory in the early 1980s. Using negative ion atmospheric pressure chemical ionization with the addition of pentafluorobenzyl alcohol to study the n -pentane through n -octane reactions and those of the fully deuterated n -alkanes, hydroxyalkyl nitrate products were identified from the n -pentane, n -heptane, and n -octane reactions for the first time and the presence of hydroxycarbonyl products was confirmed. Adding NO 2 to the chamber reaction mixture postreaction to form [NO 2 ·M] - adducts of the hydroxycarbonyls and hydroxynitrates, together with the use of 5-hydroxy-2-pentanone and 2-nitrooxy-3-butanol as internal standards for the hydroxycarbonyls and hydroxynitrates, respectively, enabled the yields of the hydroxycarbonyl and hydroxynitrate reaction products to be estimated.