An aerosol dynamics model, AERO2, is presented, which describes the formation of H
2SO
4-H
2O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO
2 and OH (
k1), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (
tn), the H
2SO
4 mass accommodation coefficient () and a measure of the turbulence intensity in the reactor (
ke). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number (
Ntot) and total volume (
Vtot) concentrations of the particles. The uncertainties on
Ntot and
Vtot are mainly due to the uncertainties on
k1, and
tn. An uncertainty factor of 20–100 still remains when the uncertainty on
k1, is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on
k1 and
tn. Values for
k1 are obtained in the reduced range 7.8 × 10
−13 to 1.0 × 10
−12 cm
3 s
−1, which is within the range found in the literature. For
tn, values in the range 10
4–10
7 are obtained, which is close to the upper bound of the range in literature. These values for
tn are in marked contrast with a recent set of experiments on nucleation in H
2SO
4-H
2O mixtures, which suggests a value for
tn of at most 10
−5.
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