After arriving in the Spokane area, a full ILS was commenced. It was terminated about 200 ft above the decision height with a missed approach. The aircraft was vectored for a second ILS. During the last 400 ft of this approach, about 3/4 to one inch of mixed rime and clear ice was picked up. The copilot visually identified the approach lights and the ILS was continued to landing. During the flare, the left wing dropped and struck the runway and was substantially damaged. Ice had formed on the leading edges of the wings in about a two inch flat plane, perpendicular to the chord line. At the time of the mishap, fog dispersal operations were in effect. The procedure involved the use of aircraft to disseminate dry ice into the fog to provide condensation nuclei. This procedure increases the fog droplet size to provide subsequent dissipation. It also reduces the temperature of the surrounding air, and in certain conditions, can attribute to airframe icing. Prevailing temperature was 33 deg.