Kinetics of the reactions of pinonaldehyde with OH radicals and with Cl atoms

The rate constant for the reaction of OH radicals with pinonaldehyde has been measured at 293 +/- 6 K using the relative rate method in the laboratory in Wuppertal (Germany) using photolytic sources for the production of OH radicals and in the EUPHORE smog chamber facility in Valencia (Spain) using the in situ ozonolysis of 2,3-dimethyl-2-butene as a dark source of OH radicals. In ail the experiments pinonaldehyde and the reference compounds were monitored by FTIR spectroscopy, and in addition in the EUPHORE smog chamber the decay of pinonaldehyde was monitored by the HPLC/DNPH method and the reference compound by GC/FID. The results from all the different series of experiments were in good agreement and lead to an average value of k(pinonaldehyde + OH) = (4.0 +/- 1.0) x 10(-11) cm(3) molecule(-1) s(-1). This result lead to steady-state estimates of atmospheric pinonaldehyde concentrations in the ppbV range (1 ppbV approximate to 2.5 X 10(10) molecule cm(-3) at 298 K and 1 atm) in regions with substantial Lu-pinene emission. It also implies that atmospheric sinks of pinonaldehyde by reaction with OH radicals could be half as important as its photolysis, The rate constant of the reaction of pinonaldehyde with Ci atoms has been measured for the first time. Relative rate measurements lead to a value of k(pinonaldehyde + Cl) = (2.4 +/- 1.4) x 10(-10) cm(3) molecule(-1) s(-1). In contrast to previous studies which suggested enhanced kinetic reactivity for pinonaldehyde compared to other aldehydes, the results from both the OH- and CI-initiated oxidation of pinonaldehyde in the present work are in line with predictions using structure-activity relationships. (C) 1999 John Wiley C Sons, Inc.