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 compound-hydroxyl (SOC-OH) radical rate constants and estimate semivolatile organic compounds' (SOCs) atmospheric half-lives because of potential for atmospheric long-range transport. We have used a bench-top photochemical reactor, along with solid-phase microextraction (SPME) and ethyl nitrite, to successfully measure the rate constants of naphthalene, linalool, biphenyl, and phenanthrene with hydroxyl (OH) radical. Biphenyl and phenanthrene underwent 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 constants for naphthalene, linalool, biphenyl, and phenanthrene with OH radical, 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 agreement with previous studies and model predictions. Based on the range of experimental 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 simplified analytical tools (such as solid-phase microextraction), can be used to measure SOC-OH rate constants.