Among the available remote sensing data to monitor the atmospheric composition, IASI, the Infrared Atmospheric Sounding Interferometer flying onboard the MetOp satellite since 2006, offers unprecedented possibilities for sounding the troposphere in near-real time and for capturing sudden changes in the atmosphere with a global coverage. This presentation will review the capabilities of IASI to contribute to several aspects of atmospheric chemistry, such as the identification of local and regional sources to improve emission inventories, the tracking of long-range transport of pollution, and the detection of unexpected events such as large fires or volcanic plumes. Illustrations will be provided for carbon monoxide, methanol, ammonia, and ash/sulfur dioxide from volcanoes. The sensitivity and errors inherent to satellite sounding in the infrared spectral range will also be discussed.