Environmental molecular surface science is an important and expanding area of current research. This presentation focuses on advances in the molecular level understanding of the chemistry that occurs on oxide and carbonate surfaces in the atmosphere. In particular, the importance of water in the surface composition and surface reactivity of two representative oxide and carbonate surfaces, MgO(100) and CaCO@sub3@(104) will be discussed. Reactions of trace atmospheric gases, including HNO@sub3@, with MgO(100) and CaCO@sub3@(104) as a function of relative humidity highlight the role of surface hydroxyl groups and molecularly adsorbed water in these reactions.