UK agricultural emissions of ammonia negatively impact human health and the vitality of aquatic and terrestrial ecosystems. There are few direct policies regulating agricultural ammonia emissions in the UK and routine surface measurements for evaluating bottom-up inventories used to inform policies and assess compliance are non-existent for fluxes and sparse for concentrations.
Satellite observations provide daily global coverage of ammonia abundances and include mature and extensively validated retrieval products from two instruments that pass overhead in the morning (called IASI) and the afternoon (called CrIS). These were used in combination with the GEOS-Chem chemical transport model to derive surface spring-summer ammonia emissions in a recently published study led by Dr Eloise Marais (UCL) with collaborators from the UK, the US, Belgium, Canada, and China. The fine-scale (monthly, ~10 km) top-down emissions, totalling 271 kilotonnes from IASI and 389 kilotonnes from CrIS, were compared to bottom-up estimates of annual emissions from the UK National Atmospheric Emission Inventory (NAEI) and best representation of seasonality of emissions in models. The satellite-derived and bottom-up ammonia emissions exhibit similar spatial features (see accompanying figure comparing the two) and have relative uncertainties of comparable magnitude (11-36%) to the NAEI (31%), but the satellite-derived emissions exceed bottom-up estimates by 27-49% and include a summer peak that is missing in models. The summer peak occurs over locations dominated by cattle farming in Northern Ireland and across western England and may be due to farming practices or warm summer temperatures. Further investigation is needed to resolve discrepancies identified in this study to better constrain a potentially large source of ammonia that is also a substantial source of the greenhouse gas methane.
This research was funded by the UK Department for the Environment, Food and Rural Affairs (DEFRA) and a NERC/EPSRC Researcher in Residence (RiR) Award.