Effect of Ozone on Nicotine Desorption from Model Surfaces: Evidence for Heterogeneous Chemistry
Assessment of secondhand tobacco smoke exposure using nicotine as a tracer or biomarker is affected by sorption of the alkaloid to indoor surfaces and by its long-term re-emission into the gas phase. However, surface chemical interactions of nicotine have not been sufficiently characterized. Here, the reaction of ozone with nicotine sorbed to Teflon and cotton surfaces was investigated in an environmental chamber by monitoring nicotine desorption over a week following equilibration in dry or humid air (0% or 65−70% RH, respectively). The Teflon and cotton surfaces had N2−BET surface areas of 0.19 and 1.17 m2 g-1, and water mass uptakes (at 70% RH) of 0 and 7.1% respectively. Compared with dry air baseline levels in the absence of O3, gas-phase nicotine concentrations decreased by 2 orders of magnitude for Teflon after 50 h at 20−45 ppb O3, and by a factor of 10 for cotton after 100 h with 13−15 ppb O3. The ratios of pseudo first-order rate constants for surface reaction (r) to long-term desorption (k) were r/k = 3.5 and 2.0 for Teflon and cotton surfaces, respectively. These results show that surface oxidation was competitive with desorption. Hence, oxidative losses could significantly reduce long-term re-emissions of nicotine from indoor surfaces. Formaldehyde, N-methylformamide, nicotinaldehyde, and cotinine were identified as oxidation products, indicating that the pyrrolidinic N was the site of electrophilic attack by O3. The presence of water vapor had no effect on the nicotine−O3 reaction on Teflon surfaces. By contrast, nicotine desorption from cotton in humid air was unaffected by the presence of ozone. These observations are consistent with complete inhibition of ozone−nicotine surface reactions in an aqueous surface film present in cotton but not in Teflon surfaces.