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Rate constants for the gas-phase reactions of the hydroxyl radical with the biogenic hydrocarbons isoprene, α- and β-pinene, and limonene were measured using the relative rate technique over the temperature range 295−364 K and at 760 Torr total pressure. OH was produced by the photolysis of H2O2, and helium was the diluent gas. The reactants were detected by on-line mass spectrometry, which resulted in high time resolution allowing for large amounts of data to be collected and used in the determination of the Arrhenius parameters. Many experiments were performed over the temperature range of interest leading to more accurate parameters than previous investigations, which have relied on rate constants measured at three or fewer temperatures. The following Arrhenius expressions have been determined for these reactions (in units of cm³ molecule^-1 s^-1):  isoprene, %@mt;sys@%2.56%@sx@%-0.31%@be@%+0.35%@sxx@%%@mx@% × 10^-11 exp[(408 ± 42)/T]; α-pinene, %@mt;sys@%1.17%@sx@%-0.18%@be@%+0.21%@sxx@%%@mx@% × 10^-11 exp[(436 ± 53)/T]; β-pinene, %@mt;sys@%1.47%@sx@%-0.21%@be@%+0.24%@sxx@%%@mx@% × 10^-11 exp[(467 ± 50)/T]; limonene, %@mt;sys@%4.20%@sx@%-0.51%@be@%+0.59%@sxx@%%@mx@% × 10^-11 exp[(401 ± 43)/T]. The Arrhenius parameters determined here for the reaction of OH with β-pinene are significantly different than the current recommendation, and the parameters given here for limonene are the first to be reported.

The rate constants for the gas-phase reactions of ozone with the biogenic hydrocarbons isoprene, α- and β-pinene, and limonene were measured using the relative rate technique over the temperature range 242−363 K and at 760 Torr total pressure. Helium was the diluent gas, and the reactants were detected by on-line mass spectrometry. The following Arrhenius expressions have been determined for these reactions (in units of cm³ molecule^-1s^-1):  isoprene, (%@mt;sys@%10.9%@sx@%-2.17%@be@%+2.70%@sxx@%%@mx@% ) × 10^-15 exp[−(1998 ± 63)/T]; α-pinene, (%@mt;sys@%0.48%@sx@%-0.18%@be@%+0.29%@sxx@%%@mx@% ) × 10^-15 exp[−(530 ± 150)/T]; β-pinene, (%@mt;sys@%1.74%@sx@%-0.36%@be@%+0.46%@sxx@%%@mx@% ) × 10^-15 exp[−(1297 ± 75)/T]; and limonene, (%@mt;sys@%2.95%@sx@%-0.61%@be@%+0.77%@sxx@%%@mx@% ) × 10^-15 exp[−(783 ± 72)/T]. The Arrhenius parameters determined here for the reactions of ozone with β-pinene and limonene are the first to be reported.

Rate constants were measured for gas-phase reactions of the hydroxyl radical (OH) with six polycyclic aromatic hydrocarbons (PAH) and four polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). These OH reaction rate constants were determined in helium at about 1 atm over various temperature ranges between 306 and 405 K. The experiments were carried out in a small, heated quartz reaction chamber sampled by on-line mass spectrometry, and OH was produced by the photolysis of O3 in the presence of H2O. Arrhenius regressions were performed with the rate constants of each compound, and the temperature dependencies were found to be slight to nonexistent. The OH reaction rate constants of PCDD/F were in agreement with those predicted by a structure−reactivity method. The resulting rate constants at 298 K (in units of 10^-12 cm³ s^-1) were as follows:  naphthalene, 23; acenaphthene, 58; fluorene, 13; phenanthrene, 27; anthracene, 190; fluoranthene, 11; dibenzo-p-dioxin, 12; 2,7-dichlorodibenzo-p-dioxin, 4.4; dibenzofuran, 3.5; and 2,8-dichlorodibenzofuran, 2.2.