Products of the gas-phase reactions of O-3 with a series of methyl-substituted ethenes

Alkenes are important constituents of ambient air in polluted urban areas and are highly reactive in the atmosphere, reacting with OH radicals, NOB radicals, and O-3. The products of the gas-phase reactions of O-3 With propene, cis-2-butene, trans-2-butene, 2-methylpropene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene were investigated, using gas chromatography with flame ionization detection and in situ Fourier transform infrared absorption spectroscopy, in the presence of sufficient cyclohexane to scavenge >90% (and generally >95%) of the OH radicals formed in these reactions. The ''primary'' carbonyl products identified and quantified from these O-3 reactions were HCHO and CH3CHO from propene; HCHO and CH3C(O)CH3 from 2-methylpropene; CH3CHO from cis-and trans-2-butene; CH3CHO and CH3C(O)CH3 from 2-methyl-2-butene; and CH3C(O)CH3 from 2,3-dimethyl-2-butene. The formation yields of these primary carbonyls were in the range 0.98-1.19 apart from the 2-methylpropene reaction where the decomposition of the [(CH3)(2)(C) over dotO(O) over dot]* biradical leads to additional formation of HCHO. In addition to the quantification of the HCHO, CH3CHO, and CH3C(O)CH3 formation yields from these reactions, CH3OH, CH2CO, CO, CO2, and CH4 were observed and quantified by FT-IR absorption spectroscopy.