The most abundant alkaline compound in the atmosphere is ammonia (NH3). NH3 neutralizes acids and contributes to the formation of aerosols and particulate matter, with potential consequences to the environment, human health, and radiative forcing. NH3 is primarily emitted by agricultural activities, livestock, natural sources, fertilizers, and biomass burning, and it is present in urban and remote environments. NH3 emissions and depositions strongly depend on environmental conditions such as temperature and moisture. NH3 has a short lifetime on the order of hours to a few days and exhibits a strong temporal and spatial variability. In this talk, first I will present the spatial and temporal variability of NH3 from two ground-based FTIR (Fourier Transform InfraRed) sites in Mexico City and 10 years of satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI). Then, I’ll show the temporal variability of NH3 from FTIR-NH3 retrievals in several urban and remote FTIR sites that are part of the Network for Detection of Atmospheric Composition Change (NDACC). Finally, I’ll show some preliminary comparisons between FTIR observations and GEOS-Chem simulations, and future work.