Rate coefficients for the reactions of hydroxyl (OH) and nitrate (NO 3 ) radicals with the six dimethylphenols have been determined at 295 ( 2 K and atmospheric pressure using the relative rate technique. Experiments were performed in a 3.91 m 3 atmospheric simulation chamber using in situ FTIR spectroscopy and gas chromatography for chemical analysis. The reactivity of the dimethylphenols is compared to other phenolic compounds and it is shown that the rate coefficients strongly depend on the number and position of the OH and CH 3 substituents around the aromatic ring. In addition, the dimethylphenol isomers appear to exhibit an opposite trend in reactivity for reaction with OH and NO 3 radicals. The rate coefficient data for the dimethylphenols and related phenolic compounds are explained in terms of known mechanistic features of the reactions. The atmospheric implications are also discussed.

The photochemical mechanism of unsaturated 1,4-dicarbonyls proceeds predominantly via a ketene–enol which isomerises to a furanone.

The products following Cl atom initiated oxidation of C2Cl4 at 700−760 Torr of air and 230−299 K in the presence and absence of NO x were investigated using three different FTIR smog chamber techniques. There was no measurable effect of temperature on the product yields. CCl3C(O)Cl and COCl2 were formed with molar yields of 68 ± 6% and 77 ± 12% in the presence of NO x and 87 ± 11% and 32 ± 4% in the absence of NO x . These results give branching ratios for the CCl3C(O)Cl and COCl2 forming channels of 0.64 and 0.36 in the presence of NO x and 0.84 and 0.16 in the absence of NO x . Contrary to a recent report by Hasson and Smith (J. Phys. Chem. A, 1999, 103, 2031), variation of the initial C2Cl4 by a factor of 300 over the range (0.016−5.6) × 1014 molecule cm-3 had no discernible effect (<10%) on the product distributions. The different product distribution observed in the presence of NO x may reflect the formation and subsequent decomposition of chemically activated C2Cl5O radicals, formed in the exothermic reaction of C2Cl5O2 with NO. The kinetics of the reaction of Cl atoms with C2Cl4 were measured in 2.0−700 Torr of air at 296 K. The results are in good agreement with the previous study by Nicovich et al. (J. Phys. Chem. 1996, 100, 680). The combined data can be described using F c = 0.6, k o = (1.8 ± 0.3) × 10-28 cm6 molecule-2 s-1 and k ∞ = (4.0 ± 0.4) × 10-11 cm3 molecule-1 s-1. Results are discussed with respect to the atmospheric chemistry of C2Cl4.

No abstract

Peroxynitrates are thermally unstable intermediates in the atmospheric degradation of hydrocarbons. New classes of peroxynitrates, alkoxyalkyl and alkoxyformyl peroxynitrates, can be formed during the atmospheric degradation of dialkyl ethers being extensively used as fuel additives. In this paper, the thermal lifetimes of methoxymethyl peroxynitrate, methoxyformyl peroxynitrate, and tertbutoxyformyl peroxynitrate [i.e., RO 2 NO 2 with R ) CH 3 OCH 2 , CH 3 OC(O), and t-C 4 H 9 OC(O), respectively] are reported at atmospheric pressure as a function of temperature. Relative concentrations of the peroxynitrates are followed in a 420-L reaction chamber in the presence of an excess of NO as a function of time via long-path IR absorption using a Fourier transform spectrometer. Thermal lifetimes at room temperature and atmospheric pressure are very short (in the order of 1 s) for CH 3 OCH 2 O 2 NO 2 ; however, for the alkoxyformyl peroxynitrates [R′OC(O)O 2 NO 2 ], the lifetimes are much longer with values similar to that of PAN. Alkoxyformyl peroxynitrates, in particular tert-butoxyformyl peroxynitrate, could accumulate to detectable levels in polluted air and thus make a contribution to the long-range transport of NO x .