Ammonia assessments: initial screening and evidence gathering (GN 020)

The first stage is to gather evidence in order to make your assessment. We advise using a tool called SCAIL to make the initial screening assessment .  

In order to use SCAIL and if required, carry out further detailed modelling, you will need the following information. 

Please note:

  • SCAIL can only be used to assess impacts over 250 metres from the development 
  • SCAIL should only be used in the Conservative MET option 
  • SCAIL cannot be used for in combination assessments 
  • The output should be printed to pdf as evidence.  

Screening distances to be used 

 The screening distance of 5 kilometres should be used unless your development is listed below. If your development is listed, please use the appropriate screening distance. 

  • For 32000 or fewer free range layers with manure belt removal : 3 km
  • For 140 or fewer Beef cattle : 3 km
  • For 32000 caged layers : 10 km
  • For 100 000 or more free range layers : 10 km
  • For 200 000 broilers : 10 km
  • For 400 or more dairy cows : 10km
  • For 32000 or more other poultry (non chicken) : 10km
  • For 1500 pigs or more : 10 km

For anaerobic digestion with a storage capacity for feedstock and/or digestate of 1000 cubic metres or more  : 10 km

In your assessment you need to consider the sensitive sites within the appropriate screening distance. 

Sensitive sites 

We consider a sensitive site to be an area that holds habitat in which species that cannot tolerate high levels of nitrogen are critical to habitat/ecosystem function. The sensitive sites can only tolerate a certain level of ammonia, the level is referred to as the Critical Level (Cle).

Some of the most sensitives sites will have a critical level of 1 µg/m3 whilst others will have critical levels of 3 µg/m3. All the sensitive sites we currently want to be assessed by applicants are on a map layer you can access below.  

The Map 

View areas considered to be sensitive on our open data map

Please follow the link, unclick the NRW operational assets and select the Air Quality tab select your area of the interactive map and zoom in to an appropriate level. In the layer list select ‘SSSI NH3 Critical Levels’ and ‘N Sensitive Ancient Woodlands and Parkland’.

This will show the areas we are concerned about and the critical level above which the habitats and species will be adversely affected, this is the appropriate critical level to use in your assessment and will either be 1 µg/m3 or 3 µg/m3.

This version of the map may be updated in future as evidence emerges of the need to protect further areas. Any changes will be advertised 3 months in advance and the evidence provided for public scrutiny. 

Other sources of ammonia 

The background level of ammonia you get from the APIS website includes sources of ammonia up to the date of publication. You need to check the local authority planning portal for any other sources that have been built or are applying for permission to be built that could affect the sensitive sites within your screening distance. In order to do this assessment each sensitive site needs to be placed at the centre of search area.

You can find out background values from the Air Pollution Information Service (APIS) website 

APIS background is given as a three year data set, you should only include sources of ammonia that have been operational after the 31st Dec of the mid year within the three-year average dataset. Sources operational before that date will be considered as part of the background.

Find information on other sources of ammonia emission on the Local Planning Authority website

Read How to carry out detailed modelling

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