During this seminar, Hugo will present recent results on the interaction of ozone with nicotine sorbed to Teflon and cotton surfaces in an environmental chamber where nicotine desorption was monitored over a week following equilibration in dry or humid air. We observed a dramatic reduction in desorption levels in the presence of ozone when nicotine was sorbed to Teflon surfaces, but that effect was only present in cotton surfaces under dry air. Nicotine desorption profiles from cotton in humid air were identical in the presence or absence of ozone. This phenomenon is ascribed to complete inhibition of ozone-nicotine surface reactions by co-sorbed water. Several oxidation products were identified in the gas phase, providing insight on the reaction mechanism. Some of them (formaldehyde, N-methylformamide) may be of concern as secondary pollutants, particularly when ozone-generating ”air cleaners” are used for environmental tobacco smoke (ETS) abatement. Oxidative losses of sorbed nicotine and reduction in its re-emission could attenuate possible biases in use of nicotine as ETS tracer.