title: Experimentally Determined Site-Specific Reactivity of the Gas-Phase OH and Cl + i-Butanol Reactions Between 251 and 340 K.
abstract: Product branching ratios for the gas-phase reactions of i-butanol, (CH3)2CHCH2OH, with OH radicals (251, 294, and 340 K) and Cl atoms (294 K) were quantified in an environmental chamber study and used to interpret i-butanol site-specific reactivity. i-Butyraldehyde, acetone, acetaldehyde, and formaldehyde were observed as major stable end products in both reaction systems with carbon mass balance indistinguishable from unity. Product branching ratios for OH oxidation were found to be temperature-dependent with the α, β, and γ channels changing from 34 ± 6 to 47 ± 1%, from 58 ± 6 to 37 ± 9%, and from 8 ± 1 to 16 ± 4%, respectively, between 251 and 340 K. Recommended temperature-dependent site-specific modified Arrhenius expressions for the OH reaction rate coefficient are (cm3molecule-1s-1): kα(T) = 8.64 × 10-18× T1.91exp(666/T); kβ(T) = 5.15 × 10-19× T2.04exp(1304/T); kγ(T) = 3.20 × 10-17× T1.78exp(107/T); kOH(T) = 2.10 × 10-18× T2exp(-23/T), where kTotal(T) = kα(T) + kβ(T) + kγ(T) + kOH(T). The expressions were constrained using the product branching ratios measured in this study and previous total phenomenological rate coefficient measurements. The site-specific expressions compare reasonably well with recent theoretical work. It is shown that use of i-butanol would result in acetone as the dominant degradation product under most atmospheric conditions.
authors.affiliation: Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration , 325 Broadway, Boulder, Colorado 80305, United States.|Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado 80309, United States.
authors.forename: Max R
authors.initials: MR
authors.lastname: McGillen
authors.affiliation: Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research , Boulder, Colorado 80307, United States.
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Tyndall
authors.affiliation: Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research , Boulder, Colorado 80307, United States.
authors.forename: John J
authors.initials: JJ
authors.lastname: Orlando
authors.affiliation: Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro , Rio de Janeiro, Brazil.
authors.forename: Andre S
authors.initials: AS
authors.lastname: Pimentel
authors.affiliation: Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro , Rio de Janeiro, Brazil.
authors.forename: Diogo J
authors.initials: DJ
authors.lastname: Medeiros
authors.affiliation: Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration , 325 Broadway, Boulder, Colorado 80305, United States.
authors.forename: James B
authors.identifier: http://orcid.org/0000-0001-9532-6246
authors.initials: JB
authors.lastname: Burkholder