Overview of tropospheric chemistry: Developments during the past quarter century and a look ahead

An overview is given of the main processes that affect tropospheric chemistry, in particular regarding the roles that are played by ozone, hydroxyl radicals, methane, carbon monoxide, NO and NO2. Model calculations are presented of the current concentrations of O-3 and OH, as well as of changes compared with pre-industrial times. Based on these calculations, proposals are presented for atmospheric budgets of CH4 and CO. The important roles of the tropics and subtropics in atmospheric chemistry are emphasized and the large changes that are expected in the developing world due to expanding agricultural and industrial activities are described. Finally, a personal view is presented of some research topics which deserve future attention.