Uptake of gas-phase ammonia. 1. Uptake by aqueous surfaces as a function of pH

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