Measurements of respiratory ammonia and the chemical neutralization of inhaled sulfuric acid aerosol in anesthetized dogs.

The extent of neutralization of inhaled H2SO4 aerosol by endogenous NH3 has been measured in the surgically isolated upper airways of anesthetized dogs. Neutralization was observed to be inversely proportional to particle size. The H2SO4 particles with initial dry diameters of 0.5 micrometer and 1.0 micrometer underwent 0.28 (+/- 0.08) and 0.06 (+/- 0.06)% neutralization per ppb of laryngeal NH3, respectively, during passage through the mouth and out of the larynx at a flow of 0.1 L/s. At either particle size, neutralization is related to the route of entry, being greater for entry via the mouth than the nose. Limited measurements for entry via the mouth show more neutralization of 0.7 micrometer particles at 0.1 L/s than at 0.2 L/s. These results are consistent with a reaction that is limited by the rate of NH4 diffusion to the particle's surface.