The CH₃CHO‐NO₃ reaction and possible nighttime PAN generation

Abstract

Kinetic studies have been made of the CH3CHO-NO 3 reaction in dilute mixtures of CH3CHO, NO•_, and N,_O5 in synthetic air at 700 torr and room temperature. During the course of the reaction, reactant and product analyses were made in situ, using long path length Fourier transform infrared spectroscopy. The major products of the reaction for these conditions are HONOr_ and CH3COO•_NO•_. All evidence suggests that the first step in the reaction sequence, NO 3 + CH3CHO• HONO,_ + CH3CO , proceeds with a rate constant, k = (2.1 + 0.4) x 10 -•5 ½m 3 molecule -• s -• at 299 + 1 K. These results, combined with other reaction rate data pertinent to tropospheric chemistry, are used to computer simulate the homogeneous chemistry of the polluted troposphere and to evaluate theoretically the nature of the nighttime chemistry. previous work. Hence the earlier conclusions as to the importance of (1) in the nighttime chemistry of the polluted troposphere must be questioned [Pitts et al., 1984]. However, recent measurements of the rate constant for the NO3-CH20 reaction by Cantrell et al. [1985] led to a value about a factor of 2 higher (k• = (6.3 _+ 1.1) x 10 -•6 cm -3 molecule -• s -1) than that of Atkinson et al. [1984]. Recently, Atkinson et al. [1984] also measured the NO3-CH3CHO rate constant and found k 2 = (1.34 +_ 0.28) x 10 -•s cm 3 molecule -• s -•. Both the k• and k 2 estimates are dependent upon the choice made for the equilibrium constant K 3. In view of the large differences observed in k• estimates to date, we felt that it is important to measure k 2 again as well.We report here on the results of our measurements and use these to judge, through computer simulations, the theoretical significance of (1) and (2) in the nighttime chemistry of the polluted troposphere. EXPERIMENTAL PROCEDURES Product AnalysisThe experimental techniques and laboratory equipment used in the present study have been discussed previously , and only a brief description need be given here. The large glass reaction cell (6.3-m length, 448-L volume) was equipped with a multiple-reflection, modified White optical system with a 5.31-m base path. In this work we employed 32 passes with a total optical path of 170 m. In each of the experiments, sufficient acetaldehyde (Fisher Scientific Reagent grade) and nitrogen dioxide (prepared from high-purity nitric oxide and ultra-high-purity oxygen, Linde) were added to the Chern., 88, 3095-3098, 1984.Tuesday, C. S., The atmospheric photooxidation of trans-butene-2

Some considerations of the origin of nighttime peroxy radicals observed in MLOPEX 2

“…Another source of nighttime free radicals in the troposphere, the NO 3 radical, has been suggested in a number of experimental and theoretical studies [Japar and Niki, 1979;Stockwell and Calvert, 1983;Pitts et al, 1984;Cantrell et al, 1985;Calvert et al, , 1994Killus and Whitten, 1985;Cantrell et al, 1986;Platt et al, 1990;LeBras et al, 1993]. NO 3 has been observed directly in the troposphere in a number of field studies [e.g., see Noxon et al, 1980;Noxon, 1983;Platt et al, 1980Platt et al, , 1984Yvon et al, 1996].…”

Peroxy radicals in the ROSE experiment: Measurement and theory

“…The measured HO rate constants were paxtitioned so that one-half of the addition occurred at the two terminal positions in isoprene. In consideration of tl-and g-pinene, addition was assumed to occur exclusively as shown in (29) For curves 1-5, (Z and B are 1.3, 0; 1.3, 0.1; 1.3, 0.2; 1.3, 0.3; 1.3, 0.4, respectively In view of theoretical expectations, the generation of peroxy radicals through nighttime chemistry [Stockwell and Calvert, 1983;Cantrell et al, 1985Cantrell et al, , 1986] was expected in this study. As we indicated previously, the current radical measurements could be influenced by a measurable contribution from PAN, especially during the nighttime hours.…”

A study of the reactions of NO3 radicals with organic sulfides: Reactivity trend at 298 K

“…CH3SO2 + NO2 CH3S03 + NO (20) The competition between reactions (17) and (19), which determines the SOZto-CH3S03H product ratio, was recently proposed by Yin et al [37]. In their study, Yin et al used a detailed mechanism to simulate DMS and SO2 temporal profiles observed at night in an outdoor chamber containing NO,-DMS-air mixtures.…”