Atmospheric chemistry of 2-pentanone and 2-heptanone

2-Pentanone and 2-heptanone are available for commercial use, which will lead to their possible release into the atmosphere where they are expected to primarily react with the hydroxyl (OH) radical and contribute to the formation of photochemical air pollution in urban and regional areas. We have studied the kinetics and products of the gasphase reactions of the OH radical with 2-pentanone and 2-heptanone at 298 +/- 2 K and atmospheric pressure of air. Using a relative rate method, rate constants for the reactions of the OH radical with 2-pentanone and 2-heptanone of (4.56 +/- 0.30) x 10-(12) and (1.17 +/- 0.11) x 10(-11) cm(3) molecule(-1) s(-1), respectively, were obtained, where the indicated errors are two least-squares standard deviations and do not include the similar to 10-15% uncertainties associated with the rate constant for the reference compound cyclohexane. Reaction products were analyzed by gas chromatography,in situ Fourier transform infrared spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). The products identified and quantified were (with their molar yields) as follows: from 2-pentanone, formaldehyde, 1.03 +/- 0.10; acetaldehyde, 0.51 +/- 0.11; propanal, 0.19 +/- 0.03; 2,4-pentanedione, 0.12 +/- 0.03; and molecular weight 147 organic nitrates, 0.12 +/- 0.04; and from 2-heptanone, formaldehyde, 0.38 +/- 0.08; acetaldehyde, similar to 0.05; propanal, similar to 0.05; butanal, 0.07 +/- 0.01; pentanal, 0.09 +/- 0.01; and molecular weight 175 organic nitrates, 0.18 +/- 0.05. API-MS analyses also showed the formation of products of molecular weight 128 and 144 from 2-heptanone, anticipated to be C-7-dicarbonyl(s) and C-7-hydroxydicarbonyl(s), respectively. While 94 +/- 13% of the reaction pathways of the 2-pentanone reaction are accounted for, it appears that a substantial fraction (>50%) of the initially formed alkoxy radicals from 2-heptanone undergo isomerization to form products which could not be quantified.