Night-time atmospheric loss process for unsaturated aldehydes:: Reaction with NO3 radicals

The rate constants for the gas-phase reactions of the NO3 radical with a series of unsaturated aldehydes (acrolein, crotonaldehyde, trans-2-pentenal, trans-2-hexenal, trans-2-heptenal, and cis-4-heptenal) have been. measured directly using a flow tube system coupled to a laser-induced fluorescence (LIF) detection system where the NO3 radical was monitored. The kinetic study was conducted in the temperature range from 298 to 433 K to investigate the temperature dependence of these reactions. This work is the first temperature-dependence study for the reactions of the nitrate radical with the above-mentioned aldehydes. The measured room-temperature rate constants for the reaction of NO3 with such unsaturated compounds (in units of 10(-14) cm(3) molecule(-1) s(-1)) are as follows: acrolein, 0.25 +/- 0.04; crotonaldehyde, 1.61 +/- 0.19; trans-2-pentenal, 2.88 +/- 0.29; trans-2-hexenal, 5.49 +/- 0.95; trans-2-heptenal, 9.59 +/- 0.19; cis-4-heptenal, 26.40 +/- 0.40. The proposed Arrhenius expressions for such reactions of NO3 are, respectively, k(1) = (1.7 +/- 3.2) x 10(-11) exp[-(3232 +/- 355)/T] (cm(3) molecule(-1) s(-1)), k(2) = (5.52 +/- 0.82) x 10(-11) exp[-(2418 +/- 57)/T] (cm(3) molecule(-1) s(-1)), k(3) = (5.4 +/- 0.3) x 10(-12) exp[-(1540 +/- 200)/T] (cm(3) molecule(-1) s(-1)), k(4) = (1.20 +/- 0.3) x 10(-11) exp[-(926 +/- 85)/T] (cm(3) molecule(-1) s(-1)), k(5) = (0.8 +/- 0.2) x 10(-12) exp[-(632 +/- 47)/T] (cm(3) molecule(-1) s(-1)), and k(6) = (0.2 +/- 0.1) x 10(-11) exp[-(657 +/- 6.0)/T] (cm(3) molecule(-1) s(-1)). Tropospheric lifetimes for these aldehydes have been calculated at night and during the daytime for typical NO3 and OH concentrations showing that both radicals provide an effective tropospheric sink for these compounds and that the nighttime reaction with NO3 radical can be an important loss process for these emitted organics and for the NO3 radicals. The present work aims to evaluate the importance of these reactions in the atmosphere and to contribute new data to the study of NO3 reactivity.