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, I will present the ground-based retrieval method for NH3 using measurements from two FTIR (Fourier Transform InfraRed) sites in Mexico City, which is the largest metropolitan area in North America with a high population density and major pollution episodes. I will present the seasonal and diurnal variabilities, and a comparison against measurements from the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument. Finally, I will discuss the future work towards using FTIR-NH3 retrievals in other urban and remote FTIR sites that are part of the Network for Detection of Atmospheric Composition Change (NDACC).