Investigation of European atmospheric ammonia using modelling and satellite data

Air pollution contributes to an estimated 8.34 million premature deaths annually, primarily due to exposure to fine particulate matter (PM) and ground-level ozone. PM consists of solid and liquid aerosols suspended in the air, with PM₂.₅ (particles less than 2.5 microns in diameter) being especially harmful due to its ability to enter the lungs and bloodstream.

Ammonia (NH₃), primarily from livestock emissions, significantly impacts air quality by contributing to the formation of secondary inorganic aerosols (SIAs), including ammonium nitrate and ammonium sulfate (key components of PM₂.₅). NH₃ has a short atmospheric lifetime (~15 hours) and can react rapidly with gases like nitric and sulfuric acid.

Historically, sulfur dioxide (SO₂) emissions led to the formation of ammonium sulfate, but a sharp decline in SO₂ levels since 1990 (mainly due to reduced use of coal and oil) has shifted the chemical balance toward increased ammonium nitrate formation, driven by the relative abundance of nitrogen oxides (NOₓ).

The short lifetime and consequent large spatiotemporal variability of NH₃ provides challenges in validating emission inventories with solely ground-based observations due to the sparsely distributed measurement network. Satellites help overcome this limitation by providing consistent observations with extensive spatial and temporal coverage.

This project uses observations from IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder) to assess total column NH₃ concentrations over the UK and Europe. Observations are interpreted using the TOMCAT global chemical transport model and its nested grid version, ZOOMCAT, to evaluate the spatial and temporal variability of NH₃ and its contribution to PM₂.₅.

We aim to constrain bottom-up NH₃ inventories, such as the National Atmospheric Emissions Inventory (NAEI), using top-down satellite-derived estimates, assessing long-term trends and emission sources. Initial comparisons between TOMCAT and retrievals from IASI and CrIS are presented.