Ammonia Network

Ammonia (NH₃) emissions are estimated to have at least doubled over the last century across Europe, concomitant with intensification of agriculture, and increase in use of nitrogen fertilizers. The main sources of NH₃ in the atmosphere are from the decomposition and volatilisation of animal wastes. Other sources include direct volatilisation from synthetic fertilizers (particularly urea), and a wide range of non-agricultural sources such as sewage, catalytic converters, wild animals and industrial processes. It is recognised that deposition of atmospheric NH₃ contributes to acidification and eutrophication processes, which can cause damage to sensitive ecosystems.

Under the UNECE Gothenburg Protocol and the National Emissions Ceilings Directive of the EU, the target of both these agreements is that NH₃ emissions should not exceed 297 kt as NH₃ by 2010, with a particular focus on reducing the extent of critical loads exceedance for acidification and eutrophication effects. Abatement of NH₃ emissions is also included in EU Integrated Pollution Prevention and Control (IPPC) for the intensive pig and poultry sectors.

In the UK, the Department for Environment, Food and Rural Affairs (DEFRA) is supporting work to monitor the air concentrations of gaseous ammonia (NH₃) and particulate ammonium (NH₄⁺) in the UK National Ammonia Monitoring Network (NAMN). Established in 1996, the objectives are to quantify temporal and spatial changes in air concentrations and deposition in NH₃ and NH₄⁺ (included since 1999) on a long term basis. The monitoring provides a baseline in the reduced nitrogen species (NHx = NH₃ + NH₄⁺), which is necessary for examining responses to changes in the agricultural sector and to verify compliance with targets set by international agreements. Data from the network are also used to test the performance of an atmospheric chemistry and transport model, FRAME that was developed at the same time with a special focus on NHx, and to contribute to national Nitrogen (N) deposition estimates.

For the ammonia network a two tiered approach is being used. There are currently 85 sites in the NAMN and the high spatial variability of ammonia concentrations demonstrates that this large number of sites is necessary.

At 56 of these sites, an active diffusion denuder methodology using the CEH DELTA (DEnuder for Long Term Atmospheric sampling) system (where power is available) is used to
provide the main spatial and temporal patterns of NH₃ across the UK. Aerosol NH₄⁺, a secondary product is spatially more even and is monitored at a subset of DELTA sites. The DELTA network is complemented by a secondary network of ALPHA (Adapted Low-cost Passive High-Absorption) samplers at a further 38 sites to assess regional and local scale variability in air NH₃  concentrations in source regions. The ALPHA sampler was designed and developed specifically for monitoring ambient concentrations of NH₃ , with a detection limit of around 0.02 µg NH₃ m-3 for monthly monitoring. To provide an ongoing validation of the ALPHA sampler, the method is calibrated against the DELTA method at 9 sites within the network.

The following criteria were used during selection of the monitoring sites:

Different areas in the UK emit NH₃ from different sources, so that the sites can be used to investigate differences between NH₃ patterns according to the dominant NH₃ source for an area. Six source types are used to classify differences: background, non-agricultural, mixed agricultural, cattle, pigs & poultry and sheep. Emissions of NH₃ are expected to respond to changes in these different sectors, and it therefore becomes possible to look at changes in NH₃ in response to sector activity as well as agricultural and environmental policies.