Different decomposition models have been developed to estimate hourly direct and diffuse solar irradiance from hourly global irradiance measurements. Besides clearness index k(t), other geometric and meteorological variables have been tested as predictors of hourly diffuse fraction, k, or hourly beam transmittance index, k(b), by means of piecewise correlations. The recent volcanic eruption of Mount Pinatubo (June 1991) was responsible for important modifications in the solar radiation fluxes. In this article we address the effect of the volcanic aerosols on the performance of some well-known empirical models, using a data set including different radiometric and meteorological variables. The study has revealed that the more pronounced performance changes affected the higher k(t) intervals associated with the lower levels of cloud cover. After the eruption, all the models present a general tendency to overestimate the direct component and underestimate the diffuse component.