Kinetic and product studies of the reactions of selected glycol ethers with OH radicals.

Glycol ethers are widely used as solvents and are hence liable to be released into the atmosphere where they may contribute to the formation of photochemical air pollution in urban and regional areas. The dominant reaction of glycol ethers in the atmosphere has been previously shown to be with OH radicals. Using a relative rate method, rate constants have been measured at 296+/-2 K for the gas-phase reactions of the OH radical with 1-butoxy-2-propanol [CH3CH2CH2CH2OCH2CH(OH)CH3], diethylene glycol ethyl ether [CH3CH2OCH2CH2OCH2CH2OH], and diethylene glycol n-butyl ether [CH3CH2CH2CH2OCH2CH2OCH2-CH2OH] of (in units of 10(-11) cm3 molecule(-1) s(-1)) 3.76+/-0.54, 5.72+/-0.85, and 7.44+/-0.94, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Products of the OH radical-initiated reactions of these glycol ethers have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography-mass spectrometry (GC-MS), in situ Fourier transform infrared (FT-IR) spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). The products identified and quantified account for 102+/-11% of the reaction products from 1-butoxy-2-propanol, 87+/-9% of those from diethylene glycol ethyl ether, and 83+/-12% of those from diethylene glycol n-butyl ether. An empirical estimation method for calculating reaction rates of alkoxy radicals under atmospheric conditions appears to fairly well predict the products formed and their yields. Detailed reaction schemes after the initial OH radical reactions are formulated for each of these glycol ethers, with the majority of the reactions involving H-atom abstraction from the CH2 groups adjacent to the ether linkage.

Atmospheric lifetimes and fates of selected fragrance materials and volatile model compounds.

Fragrance materials are semivolatile organic compounds widely used in consumer products. Despite their generally low volatility, it is expected that a fraction of these compounds will volatilize into the atmosphere, where they can photolyze, react with OH radicals, NO3 radicals and O3, and/or undergo wet and dry deposition. Using relative rate methods, rate constants have been measured at 296 +/- 2 K for the gas-phase reactions of OH radicals, NO3 radicals, and 03 with the fragrance materials 1-(1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone (OTNE), acetyl cedrene [(3R-(3a,3ab,7b,8aa))-1-(2,3,4,7,8,8a-hexahydro-3,6,8,8-tetramethyl-1H-3a,7-methanoazulen-5-yl)ethan-1-one], and HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethycyclopenta-[gamma]-2-benzopyran) as well as with isochroman which is structurally related to HHCB. Measured rate constants (in cm3 molecule(-1) s(-1) units) are OH radical reactions [OTNE, (9.85 +/- 0.88) x 10(-11); acetyl cedrene, (7.7 +/- 1.6) x 10(-11); HHCB, (2.6 +/- 0.6) x 10(-11); and isochroman, (3.7 +/- 0.6) x 10(-11)], NO3 radical reactions [OTNE, (1.71 +/- 0.19) x 10(-11) and acetyl cedrene, (4.1 +/- 1.0) x 10(-15)], and O3 reactions [OTNE, (2.1 +/- 0.5) x 10(-18) and acetyl cedrene, <2.2 x 10(-18)] where the error limits are two least-squares standard deviations. Rate constants for the OH radical reactions predicted by a structure-reactivity estimation method agree well with the measured values. The dominant tropospheric loss processes for the compounds studied are calculated to be in a reaction with OH radicals during daytime and, for OTNE and acetyl cedrene, with NO3 radicals during nighttime. The calculated atmospheric lifetimes due to daytime reaction with the OH radical are a few hours or less for the fragrance materials studied and indicate that these specific compounds will not undergo long-range transport in the atmosphere.