Abstract:   Ammonia (NH3) is the most abundant alkaline compound in our atmosphere and is involved in several reactions, including the neutralization of acids and the formation of particulate matter, with direct consequences to the environment and human health. NH3 is primarily emitted from agricultural sources, however, it is also present in urban and remote environments. NH3emissions and deposition depend strongly on environmental conditions; temperature and moisture play a crucial role in determining NH3 concentrations on diurnal to annual scales. The objective of this work is to determine and compare the temporal variability and trends of NH3 at urban and remote locations, mainly by using datasets of NH3 total columns retrieved from spectroscopic solar absorption measurements performed at twenty ground-based Fourier transform infrared (FTIR) sites that are globally dispersed in both hemispheres from 45°S to 80°N, most of them part of the Network for Detection of Atmospheric Composition Change (NDACC). In addition, I’ll show comparisons between the FTIR-NH3 data with modeled NH3 from the GEOS-Chem chemical transport model and the preliminary Tropospheric Chemistry Reanalysis (TCR-2) NH3 product. Finally, I'll present some conclusions and future work.