Uptake of Hydrogen Halides by Water Droplets

The uptake kinetics of three different hydrogen halides, i.e., HCl, HBr, and HI, by aqueous surfaces were measured as a function of temperature in the range from 262 to 281 K using the droplet train technique. The reported mass accommodation coefficients (α) were shown to decrease with increasing temperature. For HCl, α decreases from 0.24 to 0.13 when the temperature was raised from 263 to 281 K. In the same temperature range, the mass accommodation of HBr and HI decrease from 0.16 to 0.068 and 0.19 to 0.079, respectively. This temperature trend suggests that the rate-limiting step during the accommodation process is part of the physical solvation process as previously reported for nonreacting gases. The data were accordingly interpreted using a model found in the literature which describes the mass accommodation process as a dynamical nucleation event. The implications for the tropospheric chemistry of these findings are also discussed.