We used proton-transfer-reaction mass spectrometry (PTR-MS) for on-line detection of volatile trace gases produced from the reaction of ozone with human skin lipids. Initial small-scale in vitro and in vivo experiments were followed by experiments conducted with human subjects in a simulated office. Detected products included mono- and bifunctional compounds that contain carbonyl, carboxyl, or alpha-hydroxy ketone groups. Reactions between ozone and human skin lipids reduce the mixing ratio of ozone in indoor air, but concomitantly increase the mixing ratios of volatile products and, presumably, skin surface concentrations of less volatile products. Some of the volatile products, especially the dicarbonyls, may be respiratory irritants. Some of the less volatile products may be skin irritants. For more information about this seminar, please contact: Hugo Destaillats(510) 486-5897