The prime objective of the EUMETSAT Polar System (EPS) Metop mission series is to provide continuous, long-term data sets in support of operational météorologique and environmental forecasting and global climate monitoring.The Metop satellites carry on board a set of state-of-the-art sounding and imaging instruments that offer improved remote sensing capabilities to both meteorologists and climatologists.EVOSS exploits the data of the following instruments on board Metop :1) the Global Ozone Monitoring Experiment–2 (GOME-2) for retrieval of sulphur dioxide emissions and2) the Infrared Atmospheric Sounding Interferometer IASI for retrieval of sulphur dioxide and ash emissions from volcanoes.The Global Ozone Monitoring Experiment–2 (GOME-2) is an optical spectrometer, fed by a scan mirror which enables across-track scanning in nadir, as well as sideways viewing for polar coverage and instrument characterization measurements using the moon. GOME-2 senses the Earth’s backscattered radiance and extraterrestrial solar irradiance in the ultraviolet and visible part of the spectrum (240 - 790 nm) at a high spectral resolution between 0.2 - 0.4 nm. 4096 spectral points from 4 detector channels are transferred per individual GOME-2 measurement. The footprint size is 80 x 40 km for main channel data.The concept of IASI is based on the spectral decomposition of thermal heat emission from the earth, performed with a Michelson interferometer. After an inverse digital Fourier transform and radiometric calibration performed on board to control data flow, the calibrated spectra are transmitted to the ground sector.