The formation of aldehydes and organic acids was examined for the gas-phase reactions of ozone with unsaturated VOCs. Formaldehyde and formic acid were produced via the reaction of ozone with each of the three selected unsaturated VOCs: styrene, limonene, and 4-vinylcyclohexene. In addition, benzaldehyde was detected in the styrene-ozone-air reaction system, and acetic acid was found in the limonene-ozone -air system. The study also examined the gas-phase reactions involving formaldehyde, ozone, and nitrogen dioxide and found the formation of formic acid, suggesting that the nitrate radical may play an important role in converting formaldehyde into formic acid. Experiments for all the reactions were conducted by using a 4.3-m 3 Teflon chamber. Since the conditions and chemicals employed in the reactions were similar to those for indoor environments, the results from this study may be extrapolated to typical indoor situations and support indications from previous studies that certain aldehydes and organic acids could be generated by indoor chemistry. © 1994, American Chemical Society. All rights reserved.