Atmospheric fate of carbonyl oxidation products originating from alpha-pinene and Delta(3)-carene: Determination of rate of reaction with OH and NO3 radicals, UV absorption cross sections, and vapor pressures

Large yields of dicarbonyl compounds have been found in the atmospheric oxidation of alpha-pinene and Delta(3)-carene. These terpenes are emitted in large quantities by biogenic sources, and it is important to know the fate of their reaction products. In this investigation, ultraviolet and infrared absorption cross sections, vapor pressures, and rate coefficients far hydroxyl and nitrate radical reactions have been determined for the main product in each case, i.e., 3-acetyl-2,2-dimethylcyclobutaneacetalde (pinon-aldehyde) and 2,2-dimethyl-3-(2-oxopropyl)cyclopropane aldehyde (caronaldehyde). Photolysis lifetimes at noon on July 1 at 50 degrees N using a photolysis quantum yield of 1 are 3.3 h for pinonaldehyde and 5.8 h for caronaldehyde. The infrared absorption cross sections obtained (base e) were (8.08 +/- 0.32) x 10(-19) and (1.04 +/- 0.05) x 10(-18) cm(2) molecule(-1) for pinonaldehyde and caronaldehyde at 1725.4 and 1741.5 cm(-1), respectively. Vapour pressures determined by Knudsen effusion measurements are 5.1 and 3.0 Pa at 298 K. The rate coefficients obtained using the relative rate technique for reaction with OH radicals were (8.72 +/- 1.14) x 10(-11) and (1.21 +/- 0.36) x 10(-10) molecules cm(-3) s(-1) for pinonaldehyde and caronaldehyde and for the corresponding NO3 reactions were (2.35 +/- 0.37) x 10(-14) and (2.71 +/- 0.15) x 10(-14) molecules cm(-3) s(-1). The vapor pressures are too high for homogenous nucleation or direct condensation to take place in the atmosphere. The dominant gas-phase removal processes will be reaction with OH radicals and possibly also photodissociation.