Kinetics of the reactions of OH radicals with n-butyl, isobutyl, n-pentyl and 3-methyl-1-butyl nitrates

The kinetics of the reactions of n-butyl (BTN), isobutyl (IBN), n-pentyl (PTN) and 3-methyl-1-butyl (3M1BN) nitrates with OH radicals has been studied using a low pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo-first order conditions from kinetics of OH consumption in high excess of the nitrates. The overall rate coefficients, kBTN = 1.0 × 10−13 (T/298)3.36 exp(838/T) (T = 288-500 K), kIBN = 2.8 × 10−14 (T/298)4.09 exp(1127/T) (T = 283-500 K), kPTN = 1.26 × 10−12 (T/298)4.56 exp(45/T) (T = 298-496 K) and k3M1BN = 8.47×10−14 (T/298)3.52 exp(1069/T) cm3molecule−1s−1 (T = 288-538 K) (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium. The yields of the carbonyl compounds, n-butanal (n-C3H7CHO) and isobutanal ((CH3)2CHCHO), resulting from the abstraction by OH of an α-hydrogen atom in n-butyl and isobutyl nitrates, followed by α-substituted alkyl radical decomposition, were determined at T = 300 K to be 0.10 ± 0.02 and 0.15 ± 0.03, respectively. The calculated tropospheric lifetimes of BTN, IBN, PTN and 3M1BN indicate that reaction of these nitrates with OH represents an important sink of these compounds in the atmosphere.