An experimental study on the temperature dependence for the gas-phase reactions of NO3 radical with a series of aliphatic aldehydes

The absolute rate constants for the gas-phase reactions of the NO3 radical with a series of aldehydes such as acetaldehyde, propanal, butanal, pentana l, hexanal and, heptanal were measured over the temperature range 298-433 K , using a discharge flow system and monitoring the NO3 radical by Laser Ind uced Fluorescence (LIF). The measured rate constants at 298 K for the reaction of NO3, in units of 1 0(-14) cm(3) molecule(-1) s(-1), were as follows: acetaldehyde 0.32 +/- 0.0 4, propanal 0.60 +/- 0.06, butanal 1.46 +/- 0.16, pentanal 1.75 +/- 0.06, h exanal 1.83 +/- 0.36, and heptanal 2.37 +/- 0.42. The proposed Arrhenius ex pressions are k(1) = (6.2 +/- 7.5) x 10(-11) exp [-(2826 +/- 866)/T] (cm(3) molecule(-1) s(-1)), k(2) = (1.7 +/- 1.0) x 10(-11) exp [-(2250 +/- 192)/T ] (cm(3) molecule(-1) s(1)), k(3) =(7.6 +/- 9.8) x 10(11) exp [-(2466 +/- 5 05)/T] (cm(3) molecule(-1) s(-1)), k(4) = (2.8 +/- 1.4) x 10(-11) exp [-(21 89 +/- 156)/T] (cm(3) molecule(-1) s(-1)), k(5) = (7.0 +/- 1.8) x 10(-11) e xp [-(2382 +/- 998)/T] (cm(3) molecule(-1) s(-1)), and k(6) = (7.8 +/- 1.0) x 10(-11) exp [-(2406 +/- 481)/T] (cm(3) molecule(-1) s(-1)). Tropospheric lifetimes for these aldehydes were calculated at night and dur ing the day for typical NO3 and OH average concentrations and showed that b oth radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with the NO3 radical can be an important, if not dominant, loss process for these emitted organics and for NO3 radicals.