The yields of alkyl nitrates formed in the NOx-air photooxidations of the homologous series of n-alkanes from ethane through n-octane have been determined at 299 ± 2 K and 735 torr total pressure for two different chemical systems. Alkyl peroxy radicals were generated by reaction of the n-alkanes with OH radicals (generated from the photolysis of methyl nitrite in air) or Cl atoms (from photolysis of Cl2 in air). The alkyl nitrate yields obtained from the two systems, corrected for secondary reactions, were in agreement within the experimental errors and increased monotonically with the carbon number of the n-alkane, from <1% for ethane to ~33% for n-octane, with the yields apparently approaching a limit of ~35% for large n-alkanes. The relative yields of the various secondary alkyl nitrate isomers in the n-pentane through n-octane systems were in good agreement with those expected from OH radical or Cl atom reaction with the corresponding secondary C-H bonds. However, the relative yields of the primary alkyl nitrates in the propane and butane systems were a factor of ~2 lower than expected. The data are consistent with the alkyl nitrates being formed almost entirely from the reaction of peroxy radicals with NO, and the ratios of the corrected alkyl nitrate yields thus reflect the fraction of R02 radicals which react with NO to form alkyl nitrates. These nitrate yields from the reaction of R02 radicals with NO are important inputs into chemical computer models of the atmospheric NO*-air photooxidations of the large 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 ∼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.

The gas phase reactions of 0 3 with ethene, isoprene, and a series of monoterpenes have been investigated at 296 +-2 K and atmospheric pressure of air in the presence of cyclohexane at concentrations sufficient to essentially totally scavenge any OH radicals formed. The expected products of the OH radical-initiated reaction of cyclohexane, cyclohexanone and cyclohexanol, were observed in all cases. From a knowledge of the chemistry of cyclohexane in these reaction systems and as a result of cyclohexanone and cyclohexanol formation yield data obtained in subsidiary experiments, the formation yields of OH radicals in these O3-alkene reactions were derived. The OH radical formation yields obtained from the gas phase reactions of 03 with alkenes were ethene, 0.12; isoprene, 0.27; camphene, <0.18; 3-carene, 1.06; limonene, 0.86; myrcene, 1.15; ocimene (a cis-, transmixture), 0.63;/3-phellandrene, 0.14; a-pinene, 0.85;/3-pinene, 0.35; sabinene, 0.26; and terpinolene, 1.03, all with estimated overall uncertainties of a factor of --• 1.5. For a-pinene the effect of varying the water vapor concentration was investigated and no change in the OH radical formation yield was observed over the range of (2.5-24) x 1016 molecules cm -3 of water vapor. The experimental conditions were such that formation of OH radicals from HO2 radicals was of minor importance, and the OH radical formation yields given above refer to direct formation of OH radicals and not HO2 radicals. Data, 20, 459-507, 1991. Atkinson, R., and W. P. L. Carter, Kinetics and mechanisms of the gas-phase reactions of ozone with organic compounds under atmospheric conditions, Chem. Rev., 84, 437-470, 1984. Atkinson, R., and A. C. Lloyd, Evaluation of kinetic and mechanistic data for modeling of photochemical smog, J. Phys. Chem. Ref. Data, 13, 315-444, 1984. Atkinson, R., S. M. Aschmann, W. P. L. Carter, A.M. Winer, and J. N. Pitts, Jr., Alkyl nitrate formation from the NOx-air photooxidations of C2-C8 n-alkanes, J. Phys. Chem., 86, 4563-4569, 1982. Atkinson, R., S. M. Aschmann, W. P. L. Carter, A.M. Winer, and J. N. Pitts, Jr., Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO, Int. J. Chem. Kinet.,

The gas-phase reactions of O3 with a series of alkenes have been investigated at 296 ± 2 K and atmospheric pressure of air in the presence of cyclohexane at concentrations sufficient to scavenge any OH radicals formed. The expected products of the OH radical-initiated reaction of cyclohexane, cyclohexanone and cyclohexanol, were observed in all cases. From a knowledge of the chemistry of cyclohexane in these reaction systems and the cyclohexanone and cyclohexanol formation yields obtained, the following formation yields of OH radicals in these O3alkene reactions were derived: propene, 0.33; 1-butene, 0.41; 2-methylpropene, 0.84; cis-2-butene, 0.41; trans-2butene, 0.64; 2-methyl-1 -butene, 0.83; 2-methyl-2-butene, 0.89; 2,3-dimethyl-2-butene, 1.00; cyclohexene, 0.68; 1,3-butadiene, 0.08; all with estimated overall uncertainties of a factor of ~1.5.

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