Atmospheric Ammonia Monitored by IASI
Résumé
The natural nitrogen cycle is significantly perturbed by anthropogenic atmospheric emissions of reactive nitrogen compounds resulting from our production of energy and food. Ammonia (NH3) is one of the largest contributors to reactive nitrogen and the principal alkaline component in our atmosphere. In the last century global ammonia emissions have doubled and are expected to further increase in the coming decades, with huge implications on Earth's environment, climate and human health. In the atmosphere 109 NH3 rapidly forms aerosols and is therefore a species of high relevance for air quality. In Europe, it is expected to become the single most important contributor of tropospheric aerosol by 2020. As a short-lived species, ammonia is highly variable in time and space, and while ground based measurements are possible, they are sparse and not representative for larger scales. Consequently, the ammonia budget is poorly understood and accounts for the largest uncertainty in the global nitrogen cycle. The Infrared Atmospheric Sounding Interferometer (IASI), an infrared sounder onboard the MetOp platform, has demonstrated its capabilities for probing atmospheric ammonia, down to the boundary layer. We recently developed an Optimal Estimation Method on Spectral Ensemble (OEMSE) to obtain global distributions of NH3 total columns with much improved sensitivity than in previous studies, and which also allows assessing retrievals errors. This new method and daily-based global ammonia products will be presented. Comparisons with ground-based in situ measurements and model data will be provided as a first validation of the product.Based on the results, we will further assess the capabilities of IASI to monitor local sources (in terms of seasonal and inter annual variations) and transport, and to contribute, by also using model simulations, in refining emission inventories. Finally we will provide the first results of an empirical analysis of NH3 volatilization, performed by correlating the retrieved total columns to soil parameters (temperature, soil pH, relative humidity,...) and anthropological activity indicators (livestock density, intensity of fertilization, population density,...).