Yields of β-Hydroxynitrates and Dihydroxynitrates in Aerosol Formed from OH Radical-Initiated Reactions of Linear Alkenes in the Presence of NOx

Yields of beta-hydroxynitrates and dihydroxy nitrates in aerosol formed from OH radical-initiated reactions of linear C-8-C-17 1-alkenes and C-14-C-17 internal alkenes in the presence of NO, were measured using a thermal desorption particle beam mass spectrometer coupled to a high-performance liquid. chromatograph (HPLC) with UV-vis detector for identification and quantification. For 1-alkenes, total yields of beta-hydroxynitrates normalized for OH radical addition to the C=C double bond increased with carbon number, primarily because of enhanced gas-to-particle partitioning, to a plateau of 0.140 +/- 0.009 in the C-14-C-17 range, with 1-hydroxy/2-hydroxy isomer fractions of 0.7:0.3. When combined with yields measured by O'Brien et al. (O'Brien, J. M.; Czuba, E.; Hastie, D. R.; Francisco, J. S.; Shepson, P. S. J. Phys. Chem. A 1998, 102, 8903) for reactions of smaller alkenes, the results for both 1-alkenes and internal alkenes indicate that the branching ratios for the formation of beta-hydroxynitrates from the reactions of NO with P-hydroxyperoxy radicals (averaged over both isomers) increase from 0.009 for C-2 UP to 0.13-0.15 for C-14 and larger and are approximately half the values determined by Arey et al. (Arey, J.; Aschmann, S. M.; Kwok, E. S. C.; Atkinson, R. J. Phys. Chem. A 2001, 105, 1020) for the corresponding alkyl peroxy radicals. The range of branching ratios may be higher for individual isomers, but this could not be determined. It is estimated that for 1-alkenes, approximately 60-70% of OH radical addition occurred at the terminal carbon atom. Average yields of dihydroxynitrates normalized for OH radical addition were 0.039 +/- 0.006 and 0.006 +/- 0.002 for 1-alkenes and internal alkenes, with differences reflecting enhanced decomposition of beta-hydroxyalkoxy radicals formed from internal alkenes. The addition of NH3 reduced yields significantly, apparently by altering hydrogen bonding between hydroxy and peroxy groups in hydroxyperoxy radical-NO complexes, whereas adding H2O had no obvious effect.