The influence of clouds on the photochemistry of tropospheric ozone formation

Clouds have a strong effect upon global tropospheric ozone concentrations through vertical advection, radiation, aqueous chemistry and the scavenging of gas-phase species. A box model with coupled aqueous and gas-phase chemistry has been developed. We have investigated the effect of the gas-phase self reaction of the hydroperoxy radical (HO{sub 2} + HO{sub 2}) on cloud chemistry. A number of atmospheric cases with and without clouds have been simulated. The importance of the self reaction of the hydroperoxy radical and other reactions for the modeling of ozone formation, the atmospheric HO{sub x} budget and other species in clouds will be discussed. Many recent cloud modeling studies have used a rate constant for the HO{sub 2} + HO{sub 2} reaction which is much too low in clouds.