Together with partners, several ground-based Fourier-Transform Infrared Spectrometers (FTIR) are operated in the framework of the NDACC (Network for the Detection of Atmospheric Composition Change) and/or  TCCON (Total Column Carbon Observation Network). They are used to measure the concentration of trace gases in the atmosphere. Absorption spectra are recorded in the infrared spectral region using the sun as natural sources of radiation. Column abundances of H2O, N2O, CO2, CH4, CO, C2H6, HCN, O3, HCl, HF, ClONO2, and HNO3 are derived from these spectra. The aim is to record long-term trends, to obtain annual cycles, to observe polar processes, and to validate satellite data of atmospheic trace gases. The sites are:

Since 1996   IRF Kiruna, Sweden (67.8 N, 20.4 E, 420 m a.s.l.)

Since 1999   Izaña Observatory, Tenerife Island, Spain (28.3 N, 16.5 W, 2367 m a.s.l.)

Since 2009   Addis Ababa University, Ethiopia, (9.0 N, 39.0 E, 2443 m a.s.l.)

Since 2012   Altzomoni, 60 km SE of Mexico City, Mexico (19.1 N, 98.7 W, 4000 m a.s.l.)