The measured reaction probability, gamma, for the reaction of chlorine
nitrate (CIONO2) with 60 percent (by weight) sulfuric acid aerosol in
creases monotonically with particle size at 250 kelvin. The reacto-dif
fusive length (l, the effective liquid depth over which reaction occur
s) derived from these experiments is 0.037 +/- 0.007 micrometer (95 pe
rcent confidence level for precision). The reaction probability for th
e reaction of CIONO2 with 60 percent sulfuric acid aerosol doped with
similar to 7 x 10(-4) M hydrochloric acid at 250 kelvin is larger by a
bout a factor of 4 than in the absence of hydrochloric acid and varies
less with particle size (l = 0.009 +/- 0.005 micrometer), These resul
ts provide a test of the theory for gas-particle reactions and further
insight into the reactivity of atmospheric aerosol.