Mt. Pinatubo's eruption in June 1991 injected 20 million tons of S0₂ into the stratosphere. Although a substantial amount of dust was also injected, the dust particles quickly sellled from the atmosphere in a matter of several weeks. The S0₂ however, was converted to sulfuric acid that mixed with water to produce a statospheric aerosol haze. Since there is no precipitating process in the stratosphere and since the aerosols produced are small, it can take years for them to be removed by coagulation and sedimentation. In 1982, the eruption of El Chichon injected 6 million tons of S0₂ in the stratosphere and produced the largest 'dust veil' since Krakatau in 1883. All signs point to Mt. Pinatubo being even larger than El Chichon. From a solar energy production standpoint the eruption's impact is mostly apparent in a substantial reduction of direct irradiance. This effect has already been felt by solar energy producers relying on concentrating systems where energy output has decreased considerably. This paper examines direct irradiance and illuminance data from four northern mid-latitude sites to quantify the impact of the volcanic aerosol layer on the attenuation of direct solar radiation, to investigate possible changes in local cloudiness, and to predict the evolution of this situation over the coming years.