Alkyl nitrate, hydroxyalkyl nitrate, and hydroxycarbonyl formation from the NOx-air photooxidations of C5-C8 n-alkanes

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 similar to 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 NO2 to the chamber reaction mixture postreaction to form [NO2.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.