Uptake of Gas-Phase Ammonia. 1. Uptake by Aqueous Surfaces as a Function of pH

Abstract

The uptake of gas-phase ammonia by aqueous surfaces was measured as a function of temperature, gas liquid interaction time, and pH in the range 0−13. Uptake measurements at low pH yielded values of the mass accommodation coefficient (α) as a function of temperature. The mass accommodation coefficient increases as the temperature decreases, from 0.08 at 290 K to 0.35 at 260 K. Time dependence of the uptake yielded values for the Henry's law constant. Uptake measurements at high pH indicate that an ammonia surface complex is formed at the interface. Codeposition studies in which an aqueous surface, initially at pH = 4, was simultaneously exposed to both gas-phase ammonia and SO2 were also performed. In such a codeposition experiment, the species entering the liquid neutralize each other and as a result the uptake of each species is enhanced. Modeling calculations indicate that the uptake of each species is in accord with bulk liquid-phase kinetics.