Detail about the National Atmospheric Emissions Inventory (NAEI) can be found on the Defra UK-Air website. APIS does not specifically cover individual emission sources and uses a concentration map that is informed by data about large individual emission sources and monitoring data that should account for effects of smaller individual sources.
It depends on whether the farm in question is included in the annual June agricultural census/survey (and/or has cattle registered under the Cattle Tracing System). If it is, it is almost certainly included in the maps, however the exact spatial location may be different from where the model allocates the emissions, depending on the level of aggregation of the census/survey data provided, and uncertainties in the model assumptions.
The distribution of emissions uses all agricultural census data supplied by Defra and the Devolved Authorities, with data provided at different spatial resolutions (e.g. parish, 5km grid square, small areas, individual holdings). The model re-distributes this information as NH3 emissions using land cover maps and agricultural practice data, providing a statistical representation of likely emission distributions within the spatial zones (parishes etc) the data were provided at.
The original census data are provided under strict confidentiality agreements (Data Protection Act), and information on individual farms cannot be provided.
The National Atmospheric Emission Inventory (NAEI) provides emission datasets for ammonia and other pollutants on a yearly basis.