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Ammoniac (NH₃)

 Ammonia (NH₃) is an atmospheric pollutant and one of the main sources of reactive nitrogen in the atmosphere which is involved in numerous biochemical exchanges impacting all ecosystems. Large cities such as Paris (which is the most populated area in the European Union with 10.5 million people when its larger metropolitan regions are included) typically experiences strong PM pollution episodes in springtime. At this time of the year, large parts of the particles consist of ammonium sulfate and nitrate which are formed from NH₃ released during fertilizer spreading practices and transported from the surrounding areas to Paris. These particles are known to be harmful for human health inducing 2000 deaths per year and to impact the radiative budget of the Earth.

The lack of representative NH₃ measurements, its high spatio-temporal variability, and its short atmospheric lifetime contribute to the complexity of modelling atmospheric NH₃. Large uncertainties exist in NH₃ bottom-up emission inventories. These affect the performance of model simulations of its distribution. Monitoring NH₃ is thus needed to identify the spatial distribution of the major sources, address the link between NH₃ and PM2.5 formation and improve model simulations. Long-term satellite observations derived from IASI are useful to study concentrations and spatiotemporal variability of atmospheric NH₃ from the agricultural sector to gain insights on its effects on the Paris megacity air quality.

The IASI NH₃ Level 2 products, which are retrieved using a flexible and robust NH₃ retrieval algorithm (ANNI-NH3) (Van Damme et al., 2017), are distributed via the AERIS data center, with two distinct datasets: “real time” data and “climate” data. The latter was reprocessed with the ERA-Interim European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological data. This dataset will be the official Eumetsat product in 2020.

The IASI NH₃ “real time” and “climate” products are available at https://iasi.aeris-data.fr/NH3/ and https://iasi.aeris-data.fr/NH3R-I/, respectively.

Figure 1. Monthly means of NH₃ total columns derived from 10 years (2008-2017) of IASI NH3-retrieved columns.
The blue cross indicates Paris location (Viatte et al., ACPD, 2019).

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