MODELING FORMATION AND GROWTH OF H2SO4-H2O AEROSOLS - UNCERTAINTY ANALYSIS AND EXPERIMENTAL EVALUATION

An aerosol dynamics model, AERO2, is presented, which describes the formation of H2SO4-H2O 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 SO2 and OH (k1), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (t(n)), the H2SO4 mass accommodation coefficient (alpha) and a measure of the turbulence intensity in the reactor (k(e)). 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 (N(tot)) and total volume (V(tot)) concentrations of the particles. The uncertainties on N(tot) and V(tot) are mainly due to the uncertainties on k1 and t(n). 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 t(n). Values for k1 are obtained in the reduced range 7.8 x 10(-13) to 1.0 x 10(-12) cm3 s-1, which is within the range found in the literature. For t(n), 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 t(n) are in marked contrast with a recent set of experiments on nucleation in H2SO4-H2O mixtures, which suggests a value for t(n) of at most 10(-5).