A Study of the Photolysis and OH-initiated Oxidation of Acrolein and trans -Crotonaldehyde

Experiments have been conducted in the laboratory and in the outdoor smog chamber (EUPHORE) to study the photolysis and the OH-initiated oxidation of (1) acrolein (CH 2 CHCHO) and (2) trans -crotonaldehyde (CH 3 CH CHCHO). In addition, the UV−visible absorption spectra for these two unsaturated aldehydes have been determined at (298 ± 2) K, and the rate constants for OH reactions have been measured using PLP-LIF technique as function of pressure (20−300) Torr in the temperature range (243−372) K. The obtained rate constant values are k 1 = (6.55 ± 1.22) · 10 -12 exp[(333 ± 54)/ T ] and k 2 = (5.77 ± 1.14) · 10 -12 exp[(533 ± 58)/ T ] cm 3 molecule -1 s -1 . From both midday photolysis rates J 1 ≤ 2 · 10 -6 s -1 for acrolein and J 2 ≤ 1.2 · 10 -5 s -1 for trans -crotonaldehyde, measured at EUPHORE during summer, and UV−visible absorption cross sections, very low effective quantum yields were derived: Φ eff ≤ 0.005 for acrolein, and Φ eff ≤ (0.030 ± 0.006) for trans -crotonaldehyde. The major primary products of the OH-initiated oxidation were glyoxal and glycolaldehyde for acrolein and glyoxal and acetaldehyde for trans -crotonaldehyde. The obtained results indicate that at least 20% of the reaction of OH with acrolein proceeds by addition to the double bond. The atmospheric implications of the data are discussed. The major loss process is reaction with OH for the two aldehydes. Their atmospheric lifetimes are of few hours, and their impact mainly at a local scale will be the net HO x (OH, HO 2 ) production through their photooxidation and that of the shorter chain carbonyl compounds produced.