Limb sounding measurements of infra-red emission at 6.2 &mgr;m from the Earth's atmosphere have been made by the Improved Stratospheric and Mesospheric Sounder (ISAMS). This provides a pressure modulated gas-correlation signal and a wideband signal from which NO2 and aerosol extinction at 6.2 &mgr;m are jointly retrieved between 100 mb and 0.3 mb. The retrieval scheme is discussed with reference to NO2 and a qualitative comparison made with LIMS data. The ISAMS Northern hemisphere NO2 data for January 9th 1992 are then examined and the importance of dynamical factors highlighted. ¿ American Geophysical Union 1993