United Kingdom Eutrophying & Acidifying Network (UKEAP)


The UK Eutrophying and Acidifying Pollutants (UKEAP) consists of a number of networks that monitor the deposition of both eutrophying and acidifying compounds in the United Kingdom. Due to the success of emission reductions in sulphur dioxide, acidification is no longer the issue it once was, but nitrogen pollution continues to be a concern. While its main emphasis has always been the assessment of potential impacts on UK ecosystems, UKEAP also provides the background concentration field for the secondary inorganic aerosol used to produce the 1 km x 1 km maps for PM2.5 and PM10, as well as the background 1 km x 1 km map for oxides of nitrogen used for human health impact assessments.

What is measured?

Parameters Measured Monitoring sites and data
Nitrogen dioxide
Calcium in precipitation
Chloride in precipitation
Potassium in precipitation
Magnesium in precipitation
Sodium in precipitation
Phosphate as P in precipitation
Nitrate as N in precipitation
Ammonium as N in precipitation
Sulphate as S in precipitation
Non-marine sulphate as S in precipitation
Acidity in precipitation
pH in precipitation
Sulphur dioxide as S
Nitrogen dioxide as N
Strong acid in precipitation
Nitrogen dioxide (corrected)
Current sites: 48
Total sites: 149
Data availability: 01/01/1973 to 18/01/2023

What is the purpose of the network?

The purpose of the networks is to monitor the long-term trends in pollutant concentrations in rural and remote locations of the United Kingdom. Data from the networks are used to demonstrate the UKs compliance in meeting the objectives set out in The Air Quality Standards Regulations 2010 and The National Emission Ceilings Regulations 2018. The monitoring data also contributes to the UK's obligations under the UNECE Convention on Long range transboundary air pollution (CLRTP) and the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).  The measurements form an integral part of the ambient air quality models characterising air quality and deposition throughout the United Kingdom. These models include:

Modelling Ambient Air Quality (MAAQ) as part of The Air Quality Standards Regulations 2010)
Further details of how these measurements are used in compliance assessment modelling can be found on http://uk-air.defra.gov.uk. Modelled data are available from: https://uk-air.defra.gov.uk/data/pcm-data

Concentration Based Estimates of Deposition (CBED)
Further details of this work may be found on http://www.apis.ac.uk.

Fine Resolution Atmospheric Multi-pollutant Exchange (FRAME).
NAMN data used with the model for calculating ammonia concentrations in the UK at 5 km and 1 km resolution and assessing critical level exceedance. Further details of this work may be found on http://www.pollutantdeposition.ceh.ac.uk/frame

The modelled data also allows for critical loads exceedance for habitats which are sensitive to nitrogen and assessment of pressures and threats from air pollution as part of the conservation status assessments for The Conservation of Habitats and Species Regulations 2017.

How is the network run?

UKEAP is run by UKCEH and Ricardo on behalf of the Environment Agency,  Defra and the devolved administrations and consists of 5 networks:

Monitoring Methods

Precipitation Composition
  • Bulk precipitation samples are collected using the Warren-Spring sampler design used since the inception of the acid deposition monitoring network (ADMN) in 1986
  • Bulk preciptation samples are collected  on a fortnightly basis since 2002 (weekly between 1986 – 2001)
  • Co-located daily wet-only measurements at the two EMEP supersites. Digitel (DRA-12) wet only sampler
Nitrogen Dioxide
  • Palmes-type open diffusion tube measurements on 4-weekly basis
Nitric Acid, other acid gases and major components of secondary inorganic aerosol
  • Denuder (DELTA®) measurements on a monthly basis
Ammonia and Ammonium
  • Passive ALPHA® (NH3 only) and Denuder (DELTA®) (NH3 and NH4+ at AGANet sites) measurements on a monthly basis
Hourly trace gas (NH3, HNO3, HONO, HCl and SO2) and major inorganic ions in PM2.5 and PM10 (NH4+, Na+, K+, Ca2+, Mg2+, Cl-, NO3- and SO42-)
  • Monitor for AeRosol and Gases in Ambient air (MARGA®, Metrohm, NL) Hourly data resolution
High resolution mercury (gaseous elemental Hg (GEM), particulate bound Hg (PBM) in PM2.5 and gaseous oxidised Hg (GOM))
  • Tekran ® 2537x for gaseous elemental Hg (GEM). Used with Tekran ® 1130 and 1135 for speciated Hg measurements: particulate bound Hg (PBM) in PM2.5 and gaseous oxidised Hg (GOM).

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