The uptake of nitryl chloride ClNO2 by pure water and NaI solutions was studied as a function of temperature in the range from 268 to 279 K with the droplet train technique. An upper limit of 10-5 was derived for the uptake on pure water, while the uptake rate was observed to be greatly enhanced in the presence of 10-3--10-2 M iodide, yielding uptake coefficients in the range from 1.1¿10-3 to 6.6¿10-3. This enhancement is a consequence of a reaction between I- and ClNO2 where we suggest that a transfer of Cl+ to iodide is involved. We also suggest that bulk kinetics alone is unable to describe the measured uptake rate which is influenced by surface reactions. These results show that heterogeneous chemistry in concentrated aerosols may play an important role for the fate of ClNO2, and may affect the concentration of atomic chlorine in the marine boundary layer. ¿ American Geophysical Union 1995