Uptake of Gas-Phase Ammonia. 2. Uptake by Sulfuric Acid Surfaces

The uptake of gas-phase ammonia by sulfuric acid surfaces was measured as a function of temperature (248−288 K), gas−liquid interaction time (2−15 ms), and acid concentration (20−70 wt % H 2 SO 4 ) using a droplet train apparatus. The uptake coefficient increases as a function of acid concentration and reaches unity at about 55 wt % H 2 SO 4 . The increased NH 3 uptake in acid solution is apparently due to reaction between NH 3 and H + at the gas−liquid interface. The results yielded parameters required to model the reaction of NH 3 with H + at the gas−liquid interface. These uptake experiments were expanded to include a detailed study of gas transport to a moving train of droplets. An analysis of previous sulfuric acid aerosol neutralization experiments shows that the uptake of ammonia by ternary NH 3 −H 2 SO 4 −H 2 O solutions is significantly lower than that by fresh binary H 2 SO 4 −H 2 O solutions. At typical tropospheric water and ammonia vapor concentrations, NH 3 uptake coefficients need to be included in detailed microphysical models of sulfuric acid aerosols.