Modeling studies of the concurrent growth and neutralization of sulfuric acid aerosols under conditions in the human airways.

A kinetic model of coupled droplet growth, gas uptake, and chemical reaction has been used to examine the possible changes to sulfuric acid aerosols as a result of exposure to respiratory ammonia under the conditions in the human airways. Results for a wide range of initial droplet sizes and concentrations spanning the extremes of likely atmospheric conditions are presented. It is predicted that gas phase reactions of SO2 will not significantly affect the neutralizing capability of airways ammonia. The effects of physical and chemical parameters on aerosol neutralization and growth are discussed and in particular, predictions of neutralization in typical inhalation times for aerosols characteristic of severe persistent London fogs and modern urban conditions are compared. The analysis supports the suggestion that the London fog episodes were unique in the relationship of the acid droplets formed to the neutralizing capability of ammonia in the human airways and that simple extrapolation of mortality and morbidity data from such episodes to modern conditions is unlikely to be valid.