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

Abstract

Yields of beta-hydroxynitrates and dihydroxynitrates 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(x) 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 CC 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. , and 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 beta-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. , and 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 NH(3) reduced yields significantly, apparently by altering hydrogen bonding between hydroxy and peroxy groups in hydroxyperoxy radical-NO complexes, whereas adding H(2)O had no obvious effect.

Yields ofβ-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates formed from OH radical-initiated reactions of 2-methyl-1-alkenes

“…To our knowledge, the only measured β-HN yield is a value of 0.09AE 0.03 for the reaction of 2-methyl-1-propene (15). This is about half the plateau value measured here, as expected because of the small carbon number (11). The 1H2NC n isomer comprises ≈90% of the total β-HN, so the plot of yields (Fig.…”

“…2D shows the mass spectrum for peak 3; it is from a mixture of β-HN isomers, although the spectrum should be mostly from 1H2NC 15 , the dominant isomer. The primary electron ionization fragmentation channel for compounds having two adjacent functional groups is scission of the C-C bond between the groups (11 β-Hydroxynitrate Yields. The molar yields (moles of product/moles of alkene reacted) of β-HN in the particle phase are presented in Table S2.…”

“…3. Values increase with increasing carbon number primarily because vapor pressures decrease so compounds partition more to the particle phase where they are measured (11). The branching ratio for β-HN formation from the reaction of β-hydroxyperoxy radicals with NO also increases with carbon number due to enhanced stabilization of the β-hydroxyperoxy radical-NO complex, but the effect on yields is minor for C 9 -C 15 compounds (11).…”

“…The C 15 β-HN yields measured here are 0.183 AE 0.005 and 0.225 AE 0.007 with and without normalization for OH radical addition, with uncertainties of one standard deviation. Yields at carbon numbers below the plateau can be estimated by using an approach presented previously to account for the reduced stability of β-hydroxyperoxy radical-NO complexes at smaller carbon numbers (11). To our knowledge, the only measured β-HN yield is a value of 0.09AE 0.03 for the reaction of 2-methyl-1-propene (15).…”

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…13,40 In the SAMs, the double bond is located at the chain terminus where gas phase OH first interacts with the organic, which would be expected to enhance addition compared to abstraction. Enhanced reactivity due to the presence of a double bond at the interface has also been reported for the NO 3 reaction with a terminal Scheme 1 Partial mechanism for the reaction of C8QSAM with OH leading to the observed -ONO 2 and -CQO functionalities.…”