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One of the major challenges facing atmospheric sciences is to assess, understand and quantify the impact of natural and anthropogenic pollution on the quality of life on Earth on a local, regional and continental scale. It has become apparent that pollution originating from local/regional events can have serious effects on the composition of the lower atmosphere on a continental scale. However, to understand the effects of regional pollution on a continental scale there is a requirement to transcend traditional atmospheric spatial and temporal scales and attempt to monitor the entire atmosphere at the same time. In the troposphere the variability of chemical processes, of source strength and the dynamics induce important short term, i.e., sub-hourly, variations and significant horizontal and vertical variability of constituents and geophysical parameters relevant to a range of contemporary issues such as air quality. To study tropospheric composition, it is therefore required to link diurnal with seasonal and annual timescales, as well as local and regional with continental spatial scales, by performing sub-hourly measurements at appropriate horizontal and vertical resolution. Tropospheric observations from low-Earth orbit (LEO) platforms have already demonstrated the potential of detecting constituents relevant for air quality but they are limited, for example by the daily revisit time and local cloud cover statistics. The net result of this is that the troposphere is currently significantly under sampled. Measurements from Geostationary Orbit (GEO) offer the only practical approach to the observation of diurnal variation from space with the pertinent horizontal resolution. The Geostationary Tropospheric Pollution Explorer (GeoTROPE) is an attempt to determine tropospheric constituents with high temporal and spatial resolution. The paper will summarise the needs for geostationary observations of tropospheric composition and will give the mission objectives and the requirements. [Copyright &y& Elsevier]