The reactive uptake of ClONO2 on liquid sulfuric acid has been measure
d for size-selected, sub-micron aerosol in the composition range 36-54
% H2SO4 by weight at approximate to 250 K. A comparison with results f
rom studies employing bulk surfaces at similar temperatures and compos
itions shows no evidence for a dependence of the reaction probability,
Ir, on size. We use this observation to estimate an upper limit to th
e diffuso-reactive length of 26 nm for the ClONO2 + H2O reaction on 43
weight % aerosol at 248 K. But, the present values of gamma are consi
stently lower than bulk values observed at lower temperatures and simi
lar composition, suggesting that gamma is temperature dependent.