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Spatial and temporal variability of ammonia over Mexico City

Ammonia (NH 3 ) is the most abundant alkaline compound in the atmosphere and an important gas constituent around Mexico City with several consequences over the environment, human health and the radiative forcing. However, there are only a few studies about NH 3 in this megacity. The purpose of this work is to determine the variability of atmospheric ammonia over Mexico City by means of solar absorption ground-based FTIR observations from two different atmospheric observatories, one urban and the other rural, and from ammonia satellite products obtained from the Infrared Atmospheric Sounding Interferometer (IASI). Total columns of ammonia at both observatories were retrieved from FTIR spectra using Proffit 9. The diurnal variability of ammonia is different in both stations and shows a strong influence of the surrounding urban sources and meteorological conditions. The annual cycles are similar for both stations, showing a temperature dependence of the ammonia concentrations with highest values in the warm months. The IASI observations underestimate in general the ammonia total columns, but follow a similar temporal variability. Important sources of ammonia at the northeast part of the city could be identified.