Cloud Chemistry

Tbe term cloud chemistry is considered bere to comprise both cloud composition and reactions that take place in clouds. Clouds are a very special subset of tbe atmosphere because they present substantial amounts of condensed-phase water (liquid or solid) that can dissolve gases that would otherwise be present in the gas phase, and, as a consequence of condensed-phase reactions, pennit reactions to occur that would not otherwise oeem or would be much slower. In this sense " clouds may be considered to serve as catalysts of atmospberic reactions. The uptake and teaction of material in clouds, especially sulfur and nitrogen oxides and acids, has received particular attention in the context of gaining improved understanding of the processes responsible for acid deposition. Consequently, the examples developed bere focus on these chemical systems. However, much of the resulting undetstanding of these phenomena is applicable more generally to other systems.