| Abstract
| - 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 beenmeasured directly using a flow tube system coupled to a laser-induced fluorescence (LIF) detection systemwhere the NO3 radical was monitored. The kinetic study was conducted in the temperature range from 298to 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 measuredroom-temperature rate constants for the reaction of NO3 with such unsaturated compounds (in units of 10-14cm3 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. Theproposed Arrhenius expressions for such reactions of NO3 are, respectively, k1 = (1.7 ± 3.2) × 10-11 exp[−(3232 ± 355)/T] (cm3 molecule-1 s-1), k2 = (5.52 ± 0.82) × 10-11 exp[−(2418 ± 57)/T] (cm3 molecule-1s-1), k3 = (5.4 ± 0.3) × 10-12 exp[−(1540 ± 200)/T] (cm3 molecule-1 s-1), k4 = (1.20 ± 0.3) × 10-11exp[−(926 ± 85)/T] (cm3 molecule-1 s-1), k5 = (0.8 ± 0.2) × 10-12 exp[−(632 ± 47)/T] (cm3 molecule-1s-1), and k6 = (0.2 ± 0.1) × 10-11 exp[−(657± 6.0)/T] (cm3 molecule-1 s-1). Tropospheric lifetimes forthese aldehydes have been calculated at night and during the daytime for typical NO3 and OH concentrationsshowing that both radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with NO3 radical can be an important loss process for these emitted organics and for the NO3radicals. The present work aims to evaluate the importance of these reactions in the atmosphere and to contributenew data to the study of NO3 reactivity.
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