Unaccounted variability in NH₃ agricultural sources detected by IASI contributing to European spring haze episode

Abstract : Ammonia (NH₃), whose main source is agriculture, is an important gaseous precursor of atmospheric particulate matter (PM). For the first time, we derived daily ammonia emissions using NH₃ total columns from the Infrared Atmospheric Sounding Interferometer (IASI) onboard Metop-A, at a relatively high spatial resolution (grid-cell of 0.5° x 0.5°). During the European spring haze episode of March 2014 8th to 15th, IASI reveals NH₃ total column magnitudes highlighting higher NH₃ emissions over Central Europe (especially over Germany, Czech Republic and eastern France) from the ones provided by the European reference EMEP inventory. These ammonia emissions exhibit in addition a large day-to-day variability, certainly due to spreading practices. The increase of NH₃ emissions in the model, that reaches +300% locally, leads to an increase of both NH₃ and PM10 surface concentrations and allows for a better comparison with independent measurements (in terms of bias, root mean square error and correlation). This preliminary study suggest that there are good promises for better quantifying NH₃ emissions by atmospheric inversions.