Monitoring of atmospheric ammonia (NH3) in Auvergne-Rhône-Alpes region (France): comparison between satellite, ground-based observations, and simulations from a chemistry-transport model

Atmospheric ammonia (NH₃) is a gaseous precursor of secondary inorganic aerosols, which represent a significant part of concentrations of fine particulate matter PM_2.5 measured in the French region Auvergne-Rhône-Alpes (AuRA). Although French State gives an objective for reducing territorial NH₃ emissions, ammonia concentrations in ambient air are not regulated. Very few continuous measurement stations exist in France and cover a time range of a few years at most. Ammonia can also be monitored by satellite remote sensing, which offers a better spatial coverage over more than a decade. 

Atmo Auvergne-Rhône-Alpes (Atmo AuRA) is a regional observatory of air quality approved by the French State. Atmo AuRA extends its activities to the use of satellite remote sensing data as an external source of information to test the consistency of its emission cadastres, air quality forecasts and hindcasts and potentially improve them. 

Since 2015, Amo AuRA maintains a station in Lyon with an analyzer measuring continuously NH₃ mixing ratios. The association also builds regional emission inventories of air pollutants, including NH₃, and runs routinely CHIMERE chemistry-transport model to evaluate and forecast regional air quality. The chemistry-transport modeling can be used to simulate NH₃ atmospheric content for given emissions from inventories and be compared with actual measurements. 

In this study, we compare different datasets describing NH₃ atmospheric content in AuRA region. Morning in situ measurements in Lyon are compared with NH₃ level 2 data of total columns retrieved from the Infrared Atmospheric Sounding Interferometer (IASI), to evaluate their covariations on the period 2016-2021. The temporal consistency between ground measurements and simulations from CHIMERE is also investigated over the same period. Finally, a comparative analysis on CHIMERE and IASI data is done both in terms of spatial distribution and temporal evolution.