Use of a bench-top photochemical reactor and solid-phase microextraction to measure semivolatile organic compound-hydroxyl radical rate constants

It is increasingly important to be able to measure semivolatile organic com pound-hydroxyl (SOC-OH) radical rate constants and estimate semivolatile or ganic compounds' (SOCs) atmospheric half-lives because of potential for atm ospheric long-range transport. We have used a bench-top photochemical react or, along with solid-phase microextraction (SPME) and ethyl nitrite, to suc cessfully measure the rate constants of naphthalene, linalool, biphenyl, an d phenanthrene with hydroxyl (OH) radical. Biphenyl and phenanthrene underw ent wall loss in the reactor. The wall loss rates were determined and were used to correct the measured gas-phase rate constants. The reaction rate co nstants for naphthalene, linalool, biphenyl, and phenanthrene with OH radic al, in our bench-top system at 295 +/- 3 K, were determined to be 2.73 +/- 0.37 x 10(-11), 1.93 +/- 0.24 x 10(-10), 7.44 +/- 1.9 x 10(-12), 1.73 +/- 0 .21 x 10(-11) (cm(3)/moleculels), respectively, and were in excellent agree ment with previous studies and model predictions. Based on the range of exp erimental and predicted rate constants for these reactants and an estimated average OH concentration in the atmosphere, the atmospheric half-lives of these SOCs are significantly less than 2 d. This indicates that the global presence of these compounds in the atmosphere is primarily due to regional sources and not to atmospheric long-range transport. This study shows that bench-top reactors, combined with corrections for reactant wall loss and si mplified analytical tools (such as solid-phase microextraction), can be use d to measure SOC-OH rate constants.