The mechanisms for the Cl‐initiated and OH‐initiated atmospheric oxidation of t‐butyl alcohol (TBA), methyl t‐butyl ether (MTBE), and dimethyl ether (DME) have been determined. For TBA the only products observed are equimolar amounts of H2CO and acetone, and its atmospheric oxidation can be represented by (7), The mechanism for the atmospheric oxidation of DME is also straight forward, with the only observable product being methyl formate, The mechanism for the atmospheric oxidation of MTBE is more complex, with observable products being t‐butyl formate (TBF) and H2CO. Evidence is presented also for the formation of 2‐methoxy‐2‐methyl propanal (MMP), which is highly reactive and presumably oxidized to products. The atmospheric oxidation of MTBE can be represented by (9) and (10), In terms of atmospheric reactivity, DME, TBA, and MTBE all compare favorably with methanol. In terms of rate of reaction in the atmosphere, DME, MTBE, and TBA are 1.4, 0.40, and 0.28 times as reactive as CH3OH towards OH on a per carbon basis. With regard tochemistry, atmospheric oxidation of CH3OH yields highly reactive H2CO as the sole carbon‐containing product. In contrast, only 25% of the carbon in TBA is converted to H2CO, with the balance yielding unreactive acetone. For DME, all the carbon is converted to methyl formate which is unreactive. Finally, for MTBE, 60% is converted to unreactive TBF while the remaining 40% produces highly reactive MMP. Final assessment of the impact of these materials on the atmospheric reactivity of vehicle emissions requires the determination of their emissions rates under realistic operating conditions.

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of CH 3 C(O)OCH 3 in 700 Torr of N 2 /O 2 at 296 K. Relative rate techniques were used to measure 0 ( 0.1) × 10 -13 , and k. The reaction of Cl+CH 3 C(O)OCH 3 was found to proceed more than 95% via H-abstraction at the -OCH 3 site. The fate of the CH 3 C(O)OCH 2 O‚ radical was studied in 700 Torr of N 2 /O 2 diluent at 296 K in the absence and presence of NO. Two loss mechanisms were identified: reaction with O 2 to give CH 3 C(O)OC(O)H and R-ester rearrangement to give CH 3 C(O)OH and HCO‚ radicals. It was found that R-ester rearrangement is more likely when CH 3 C(O)-OCH 2 O‚ radicals were produced via the CH 3 C(O)OCH 2 O 2 ‚ + NO reaction than when they were produced via the self-reaction of peroxy radicals. In one atmosphere of air ([O 2 ] ) 160 Torr) containing NO at 296 K it can be calculated that 65 ( 14% of the CH 3 C(O)OCH 2 O‚ radicals undergo R-ester rearrangement while 35 ( 5% react with O 2 .

The UV absorption spectrum and kinetics of the self reaction of CH3OCH202 at 298 K have been studied using both the modulated photolysis of C12/CHsOCH3/02/N2 mixtures and the pulse radiolysis of SFs/CH3OCHp/ 0 2 mixtures. The spectrum, characterized in the range 200-290 nm, is in good agreement with the single published determinatiom8 The observed second-order removal kinetics of CH30CH202, ks,a, were found to be sensitive to both the variation of total pressure (1 7-760 Torr) and the composition of the reaction mixtures:2CH3OCH202 -2CH3OCH20 + 0 2 (sa); -CH3OCHO + CH3OCH20H + 0 2 (5b). The kinetic studies and a detailed product investigation using long path length FTIR spectroscopy (T = 295 K, C12/CHoOCHs/ 0 2 / N 2 system) provide evidence to support a mechanism involving the rapid thermal decomposition of CH3-OCH2O by H atom ejection occurring in competition with thereaction with 0 2 : CHsOCHtO (+M) -CH30CHO + H (+M) (6); CH3OCH20 + 0 2 -CH30CHO + HO2 (4). The complications in the measured values of ksoh in the present studies, and those reported previously,8 are believed to occur as a direct result of formation of H atoms from reaction 6. Accordingly, a pressure-independent value of k5 = (2.1 f 0.3) X 1@l2 cm3 molecule-' s-I is derived for the elementary rate coefficient at 298 K, with identical values of the branching ratio a = ksa/ks = 0.7 f 0.1 determined independently from the FTIR product studies and the modulated photolysis experiments. As part of this work, the rate coefficient for the reaction of C1 atoms with CH3OCHzCl was found to be (2.9 f 0.2) X 10-l' cm3 molecule-l s-l.

No abstract

Pulse radiolysis and FT-IR smog chamber experiments were used to investigate the atmospheric fate of C6H5O(•) radicals. Pulse radiolysis experiments gave σ(C6H5O(•))235  nm = (3.82 ± 0.48) × 10-17 cm2 molecule-1, k(C6H5O(•) + NO) = (1.88 ± 0.16) × 10-12, and k(C6H5O(•) + NO2) = (2.08 ± 0.15) × 10-12 cm3 molecule-1 s-1 at 296 K in 1000 mbar of SF6 diluent. No discernible reaction of C6H5O(•) radicals with O2 was observed in smog chamber experiments, and we derive an upper limit of k(C6H5O(•) + O2) < 5 × 10-21 cm3 molecule-1 s-1 at 296 K. These results imply that the atmospheric fate of phenoxy radicals in urban air masses is reaction with NO x . Density functional calculations and gas chromatography−mass spectrometry are used to identify 4-phenoxyphenol as the major product of the self-reaction of C6H5O(•) radicals. As part of this study, relative rate techniques were used to measure rate constants for reaction of Cl atoms with phenol [k(Cl + C6H5OH) = (1.93 ± 0.36) × 10-10], several chlorophenols [k(Cl + 2-chlorophenol) = (7.32 ± 1.30) × 10-12, k(Cl + 3-chlorophenol) = (1.56 ± 0.21) × 10-10, and k(Cl + 4-chlorophenol) = (2.37 ± 0.30) × 10-10], and benzoquinone [k(Cl + benzoquinone) = (1.94 ± 0.35) × 10-10], all in units of cm3 molecule-1 s-1. A reaction between molecular chlorine and C6H5OH to produce 2- and 4-chlorophenol in yields of (28 ± 3)% and (75 ± 4)% was observed. This reaction is probably heterogeneous in nature, and an upper limit of k(Cl2 + C6H5OH) ≤ 1.9 × 10-20 cm3 molecule-1 s-1 was established for the homogeneous component. These results are discussed with respect to the previous literature data and to the atmospheric chemistry of aromatic compounds.