The particel-gas euqilibria of ammonia and nicotine in mainstream cigarette smoke have beeen studied b ydiffusion denuder collection. The surface deposition rate of nicotine is observed to decrease as the smoke traverses the denuder, and this efect is attributed to a changing particle nicotine vapor pressure driven by the measured rapid loss of volatile ammonia from particles, an interpetation 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/cm~2 for an American belended cigarette, and (approx)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 measruements predicts tha the incotine 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 partculate 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 cigaretts,. 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.
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