Combining solar light with photocatalysts can destroy a variety of dangerous pollutants in air and water.  Additionally, photoactive materials are also naturally present in the atmosphere, having a potential to initiate various atmospheric reactions. Both natural and engineered photocatalytic systems can significantly affect the quality of our environment. However, there are still many challenges concerning the efficiency and reliability of these engineered systems. In this project, various novel photocatalytic materials more active than the conventional materials under both UV and visible light have been developed.  These include: (a) metal nanoparticles modified TiO2 and (b) doped TiO2. The fundamental and applied aspects of visible-light absorbing materials in model systems using various surface science techniques have been also investigated.  Finally we have explored naturally occurring photoactive materials in mineral aerosols and their effect on air quality.