CARBONYL PRODUCTS OF THE OZONE-UNSATURATED ALCOHOL REACTION

Carbonyl products of the gas phase reaction of ozone with four monosubstituted and three 1,2-disubstituted unsaturated alcohols that are relevant to biogenic emissions have been identified in laboratory experiments involving unsaturated alcohol-ozone mixtures in the dark. Cyclohexane was added to scavenge the hydroxyl radical, which forms as a product of the ozone-unsaturated alcohol reaction. Major carbonyl products included formaldehyde and hydroxyacetaldehyde from allyl alcohol, acetaldehyde, and hydroxyacetaldehyde from 2-buten-1-ol, propanal, and hydroxyacetaldehyde from cis-2-penten-1-ol, formaldehyde from 3-buten-2-ol, 1-penten-3-ol, and 2-methyl-3-buten-2-ol, and hydroxyacetaldehyde from 2-buten-1,4 diol. Yields of the primary carbonyls (ozone + unsaturated alcohol --> 2 primary carbonyls + 2 biradicals) averaged 0.91 +/- 0.29, which compares to a theoretical value of 1.0. Yields of carbonyls that are not hydroxy substituted averaged 0.38 +/- 0.13, which compares to a theoretical value of 0.50 if one assumes that the alkyl-substituted and the hydroxyalkyl-substituted biradicals are formed in equal yields. The corresponding reaction mechanisms are outlined with focus on similarities between unsaturated alcohols and alkene structural homologues. Possible decomposition pathways for hydroxyalkyl-substituted biradicals are examined. The atmospheric persistence and the fate of unsaturated alcohols from biogenic emissions and of their carbonyl products are briefly discussed.