Particle-Gas Equilibria of Ammonia and Nicotine in Mainstream Cigarette Smoke
The particle-gas equilibria of ammonia and nicotine in mainstream cigarette smoke have been studied by diffusion denuder collection. The surface deposition rate of nicotine is observed to decrease as the smoke traverses the denuder, and this effect is attributed to a changing particle nicotine vapor pressure driven by the measured rapid loss of volatile ammonia from the particles, an interpretation that differs from that of prior studies. The rapid ammonia deposition is observed to be complete at a length-to-flow rate ratio of 28 s/cm2 for an American blended cigarette, and ∼38% of the total ammonia analyzed in the collected smoke appears to be nonvolatile in the aerosol, possibly bound in the particles by reaction with acids. Fitting of a theoretical model that predicts the rapid ammonia loss and changing nicotine vapor pressure to the measurements predicts that the nicotine vapor pressure over the particles in fresh smoke is about 6% of the pure component nicotine value, and the ammonia vapor pressure over the smoke particulate is considerably less than that predicted by its aqueous Henry's law coefficient. Dilution of mainstream smoke enhanced the fractional deposition of both ammonia and nicotine in the denuder tubes and provided a means to estimate the nonvolatile ammonia fraction, which varied considerably in cigarettes made with different tobacco types. Among the different tobacco type cigarettes, smoke ammonia concentration, "smoke pH," and smoke nicotine-to-particulate ratio varied with ammonia and nicotine deposition from diluted smoke when extreme values for an all burley tobacco cigarette were included in the analysis, but no trends were apparent when only the more typical range of the other cigarettes was considered.