Determining tropospheric concentrations of trace gases from space

It is now possible to determine the concentrations of atmospheric constitue nts in the troposphere from satellite data, a development that heralds a ne w era in tropospheric chemistry Some of the methods for retrieving troposph eric trace gases are described here, together with some of the latest resul ts obtained from ESA Earth Observation (EO) measurements. The likely conseq uences for environmental monitoring and policy are outlined, as is the new Troposat project, the aim of which is to exploit these results, together wi th the requirements for future instrumentation, to build on the present sit uation.