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 % H2SO4) using a droplet train apparatus . The uptake coefficient increases as a function of acid concentration and reaches unity at about 55 wt % H2SO4. The increased NH3 uptake in acid solu tion is apparently due to reaction between NH3 and H+ at the gas-liquid int erface. The results yielded parameters required to model the reaction of NH 3 with H+ at the gas-liquid interface. These uptake experiments were expand ed to include a detailed study of gas transport to a moving train of drople ts. An analysis of previous sulfuric acid aerosol. neutralization experimen ts shows that the uptake of ammonia by ternary NH3-H2SO4-H2O solutions is s ignificantly lower than that by fresh binary H2SO4-H2O solutions. At typica l tropospheric water and ammonia vapor concentrations, NH3 uptake coefficie nts need to be included in detailed microphysical models of sulfuric acid a erosols.