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Published February 26, 1996 | public
Journal Article

Atmospheric Chemistry of 1-Octene, 1-Decene, and Cyclohexene: Gas-Phase Carbonyl and Peroxyacyl Nitrate Products


Atmospheric reactions of 1-octene, 1-decene, and cyclohexene have been studied in laboratory experiments involving alkene−ozone mixtures in the dark and alkene−NO and aldehyde−NO mixtures in sunlight. Major carbonyl products of the alkene−ozone reaction (with sufficient cyclohexane added to scavenge OH) were heptanal from 1-octene, nonanal from 1-decene, formaldehyde from both, and pentanal from cyclohexene. For 1-octene and 1-decene, carbonyl formation yields were consistent with the simple mechanism:  RCH = CH_2 + O_3 → 0.5(HCHO + RCHOO) + 0.5(RCHO + H_2COO). Other carbonyls were formed and accounted for ca. 0.10−0.20 of the subsequent reactions of the RCHOO biradical. Pentanal accounted for ca. 0.16 of the cyclohexene−O_3 reaction. Sunlight irradiation of alkene−NO and aldehyde−NO mixtures leads to carbonyls, alkyl nitrates, and peroxyacyl nitrates. Major carbonyl products of the OH−alkene reaction were heptanal from 1-octene, nonanal from 1-decene, and formaldehyde from both. Experimental data indicated that addition is an important pathway of the overall OH−1-alkene reaction, decomposition is important for the β-hydroxyalkoxy radicals that form following OH addition, and reaction with O2 is of some importance for the alkoxy radicals that form in several pathways in the alkene−NO (sunlight), aldehyde−NO (sunlight), and peroxyacyl nitrate−NO (dark) systems. The extent of isomerization of alkoxy and β-hydroxyalkoxy radicals could not be assessed. Several peroxyacyl nitrates [RC(O)OONO_2] were formed including those with R = n-C_4H_9 from cyclohexene, R = n-C_5H_(11) from hexanal, and R = n-C_6H_(13) from heptanal and from 1-octene. The thermal decomposition rates of n-C_5H_(11)C(O)OONO_2 and n-C_6H_(13)C(O)OONO_2, which were synthesized in the liquid phase and were characterized in a number of tests using electron capture gas chromatography, were (in units of 10^(-4) s^(-1)) 0.72−2.02 (T = 291−299 K) and 0.61−1.19 (T = 291−295 K), respectively, at p = 1 atm of air. Comparison with data for lower molecular weight homologues including PAN (R = CH_3) suggests that the thermal stability of peroxyacyl nitrates may increase with the size of the n-alkyl substituent. The atmospheric persistence of the atmospheric oxidation products of 1-octene, 1-decene, and cyclohexene is briefly discussed.

Additional Information

© 1996 American Chemical Society. Received for review August 10, 1995. Revised manuscript received November 8, 1995. Accepted November 8, 1995. This work has been supported in part by the U.S. Environmental Protection Agency Center on Airborne Organics (R-819714-01-0); by National Science Foundation grant ATM-9307603; by the Coordinating Research Council, Inc., Project AQ-1-2; and by internal R&D funds, DGA, Inc., Ventura, CA. Work presented in part as papers ENVR-105 and ENVR-107, 209th National Meeting of the American Chemical Society, Anaheim, CA, April 2−7, 1995.

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