How to get the most out of APIS - FAQ

Understanding APIS data
Critical loads

What is the meaning of 'keq' in keq/ha/year?

Keq stands for kiliequivalent. This helps to distinguish between the amount of a certain element within a whole molecule. For example, the nitrogen in ammonia, NH3.

The unit known as equivalent, eq (a keq is 1000 eq), refers to the molar equivalent of e.g. sulphur, oxidised and reduced nitrogen, as well as base cations. For example:

1 keq N ha-1 yr-1 is equal to 14 kg N ha-1 yr-1 and

1 keq S ha-1 yr-1 is equal to 16 kg S ha-1 yr-1.

When converting compounds the valency is important and is connected with the charge on the ion. For example: NH4+ or NO3- have a valency of 1.

For sulphur, the prevalent ion is sulphate SO42-, which has a double charge (valency). The full process is to convert kg to kmoles, then kmoles to keq. The 'equivalent' refers to the ionic charge on an ion. 1 kmole SO42- is 2 keq, (because of the double - charge) and 1 keq SO4 is 32/2 or 16 kg S.

Why are there data missing about Areas/Sites of Special Scientific Interest in some of the critical level/load datasets for download?

Some of the conservation agencies have provided information to National Vegetation Classification level for A/SSSIs (England primarily) and some have not. Where this level of detail is not available, the broad habitat classification has been used. In some cases, several critical loads may apply to habitats within this broad classification and as such, APIS advises to seek site specific advice from the relevant authority (eg conservation agency or site manager).

Where can I find data about critical loads, levels and background concentration and deposition for UK national (SSSIs) and international protected sites?

You can use the Site Relevant Critical Loads tool to look up individual sites to get critical load information and deposition and concentration data at a particular site. . Information about critical loads themselves can be found on the quick link pages. The full downloadable data is also available on UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC).

Which acidity critical load values (CLmax S, CLminN, etc) should be used in risk assessment and how can it be reported?

The acidity critical loads values are based on a 1km grid for the UK. Consequently, for sites that are larger than 1 km2 will have many critical load grid squares covering the site. For this reason we give a maximum and minimum set of critical loads. For initial assessments, the minimum set of critical levels should be used as this follows the precautionary approach.

The critical load function tool provides a % of critical load for process contribution, background and predicted environmental concentration (eg process contribution plus background).

 

What do the CLMaxN and CLMinN mean in acidity critical loads?

The acidity critical loads have a nitrogen component and sulphur component. APIS has provided a tool to help determine where there is exceedance of acidity critical loads.

This is available on the APIS website under Quick Links>> Critical Load Function Tool or the following URL will take you directly there. The critical load explanation pages are available at in the Guide to Critical Levels and Loads in the Quick links.

Critical levels

Why are there data missing about Areas/Sites of Special Scientific Interest in some of the critical level/load datasets for download?

Some of the conservation agencies have provided information to National Vegetation Classification level for A/SSSIs (England primarily) and some have not. Where this level of detail is not available, the broad habitat classification has been used. In some cases, several critical loads may apply to habitats within this broad classification and as such, APIS advises to seek site specific advice from the relevant authority (eg conservation agency or site manager).

Where can I find data about critical loads, levels and background concentration and deposition for UK national (SSSIs) and international protected sites?

You can use the Site Relevant Critical Loads tool to look up individual sites to get critical load information and deposition and concentration data at a particular site. . Information about critical loads themselves can be found on the quick link pages. The full downloadable data is also available on UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC).
CBED

What monitoring data is used in the pollutant data on APIS?

Background pollution data for the UK is updated every year using the latest measurement data from the various networks around the UK.

For example, when considering  ammonia we use measurement data from the Ammonia Network and then produce yearly pollutant maps (5km) which are outputted by the CBED model. This is done through a kriging methodology/interpolation. To help with the spatial distribution of ammonia we run our national transport model (FRAME) which gives us a spatial pattern of the ammonia concentrations which are ‘calibrated’ relative to annual ammonia measurements. This provides the local scale variability that cannot be derived from the network measurement data on their own. More information about CBED is available here.

Emissions

What emission sources are expected to be included in APIS "background" concentration and deposition values?

APIS concentration and deposition data is updated annually as a three-year average to account for variation in precipitation and temperature between years. When considering whether a specific emission source would be included in this, it is important to understand when the emission source began operation or was given permission. Emission sources could be included both via the measurement network and also the spatial mapping we do with the national model as that includes emissions from the National Atmospheric Emissions Inventory (NAEI) https://naei.beis.gov.uk/data  (this is done yearly). Typically, emission sources are considered to be in APIS background if they were operational by 31 Dec of the mid year within the three-year average dataset.

Is there anyway to find out if ammonia emissions from a particular farm is included in the NAEI emissions inventory?

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.

Background data

Is the background concentration and deposition data in the Search by Location tool estimated from measured or modelled data scenarios?

Nitrogen deposition to woodland/forest deposits at a higher rate than to shorter vegetation types. So even at the same location different habitats can receive different depositions of pollutant. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation.

What monitoring data is used in the pollutant data on APIS?

Background pollution data for the UK is updated every year using the latest measurement data from the various networks around the UK.

For example, when considering  ammonia we use measurement data from the Ammonia Network and then produce yearly pollutant maps (5km) which are outputted by the CBED model. This is done through a kriging methodology/interpolation. To help with the spatial distribution of ammonia we run our national transport model (FRAME) which gives us a spatial pattern of the ammonia concentrations which are ‘calibrated’ relative to annual ammonia measurements. This provides the local scale variability that cannot be derived from the network measurement data on their own. More information about CBED is available here.

Is there anyway to find out if ammonia emissions from a particular farm is included in the NAEI emissions inventory?

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.

What are the dry deposition velocities used for the different gases for different habitats?

Deposition velocities are used in calculating deposition of nitrogen and sulphur. Different gases have different rates of deposition (and different deposition velocities) .

Deposition velocities are also different for different habitats. For example the rate of deposition of pollutants to forest vegetation is generally around twice that of deposition to short-vegetation. Forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a more shorter type of vegetation habitat types.

In the Search by Location tool, why is deposition different for deciduous woodland and neutral grassland in the same grid reference?

Reactive nitrogen deposits  to woodland/forest at a higher rate than to shorter vegetation types. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation. So even at the same location different habitats can receive different depositions of pollutant.

APIS provides the appropriate deposition values for each of the main habitats using either short vegetation (labelled moorland) or tree (woodland) deposition velocities.

Where can I find data about critical loads, levels and background concentration and deposition for UK national (SSSIs) and international protected sites?

You can use the Site Relevant Critical Loads tool to look up individual sites to get critical load information and deposition and concentration data at a particular site. . Information about critical loads themselves can be found on the quick link pages. The full downloadable data is also available on UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC).

Is the data in APIS available in a raw format such as xls or csv?

The most recent datasets for APIS can be downloaded from the UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC).

Can I get the data for all grid squares in the Search by Location Tool?

Nitrogen and acid deposition and ammonia background pollution data for the UK (5km grid resolution) are available on the Centre for Ecology and Hydrology Environmental Information Data Centre along with matches for habitats to critical loads.



UK datasets for SO2 and NOx pollutants (1 km grid resolution) can be found on Defra's Pollution Climate Mapping (PCM) pages.

How often is APIS data collated?

In APIS background data are calculated on an annual basis but provided as rolling 3-year means.

Is the N deposition provided for 5km grid square the total N deposition within that 5km grid square or an average over that 5km grid square?

It is the total deposition which is based on interpolating/krigging methods from a measured network to create a 5km grid. Some parts of the total (dry deposition NH3) are from modelled output.

Does APIS have data about change in nitrogen deposition over time?

We have incorporated a feature in the Site Relevant Critical Loads tool which allows you to look at the trends in pollutant concentrations/deposition at protected nature conservation sites.  On the results pages of your chosen site there is a "tab" which labelled "Trends".  The data only go as far back as 2005 and displays the three-year average background data.

What emission sources are expected to be included in APIS "background" concentration and deposition values?

APIS concentration and deposition data is updated annually as a three-year average to account for variation in precipitation and temperature between years. When considering whether a specific emission source would be included in this, it is important to understand when the emission source began operation or was given permission. Emission sources could be included both via the measurement network and also the spatial mapping we do with the national model as that includes emissions from the National Atmospheric Emissions Inventory (NAEI) https://naei.beis.gov.uk/data  (this is done yearly). Typically, emission sources are considered to be in APIS background if they were operational by 31 Dec of the mid year within the three-year average dataset.

Deposition Velocity

What are the dry deposition velocities used for the different gases for different habitats?

Deposition velocities are used in calculating deposition of nitrogen and sulphur. Different gases have different rates of deposition (and different deposition velocities) .

Deposition velocities are also different for different habitats. For example the rate of deposition of pollutants to forest vegetation is generally around twice that of deposition to short-vegetation. Forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a more shorter type of vegetation habitat types.

In the Search by Location tool, why is deposition different for deciduous woodland and neutral grassland in the same grid reference?

Reactive nitrogen deposits  to woodland/forest at a higher rate than to shorter vegetation types. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation. So even at the same location different habitats can receive different depositions of pollutant.

APIS provides the appropriate deposition values for each of the main habitats using either short vegetation (labelled moorland) or tree (woodland) deposition velocities.

Habitats protected sites

How can I visualise APIS data for long features such as a river?

The data available on APIS can be found at on the UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC). This can then be loaded into a mapping or geographical information system tool to view the data over large features.

For GIS files for protected sites across the UK you can visit JNCC’s data pages for SAC and SPA sites. For A/SSSI GIS files you can obtain them from the individual agency websites.

Why are there data missing about Areas/Sites of Special Scientific Interest in some of the critical level/load datasets for download?

Some of the conservation agencies have provided information to National Vegetation Classification level for A/SSSIs (England primarily) and some have not. Where this level of detail is not available, the broad habitat classification has been used. In some cases, several critical loads may apply to habitats within this broad classification and as such, APIS advises to seek site specific advice from the relevant authority (eg conservation agency or site manager).

Mapping

How can I visualise APIS data for long features such as a river?

The data available on APIS can be found at on the UK Centre for Ecology and Hydrology's Environmental Information Data Centre (EIDC). This can then be loaded into a mapping or geographical information system tool to view the data over large features.

For GIS files for protected sites across the UK you can visit JNCC’s data pages for SAC and SPA sites. For A/SSSI GIS files you can obtain them from the individual agency websites.

Modelling

Is the background concentration and deposition data in the Search by Location tool estimated from measured or modelled data scenarios?

Nitrogen deposition to woodland/forest deposits at a higher rate than to shorter vegetation types. So even at the same location different habitats can receive different depositions of pollutant. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation.

What monitoring data is used in the pollutant data on APIS?

Background pollution data for the UK is updated every year using the latest measurement data from the various networks around the UK.

For example, when considering  ammonia we use measurement data from the Ammonia Network and then produce yearly pollutant maps (5km) which are outputted by the CBED model. This is done through a kriging methodology/interpolation. To help with the spatial distribution of ammonia we run our national transport model (FRAME) which gives us a spatial pattern of the ammonia concentrations which are ‘calibrated’ relative to annual ammonia measurements. This provides the local scale variability that cannot be derived from the network measurement data on their own. More information about CBED is available here.

Is there anyway to find out if ammonia emissions from a particular farm is included in the NAEI emissions inventory?

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.

What are the dry deposition velocities used for the different gases for different habitats?

Deposition velocities are used in calculating deposition of nitrogen and sulphur. Different gases have different rates of deposition (and different deposition velocities) .

Deposition velocities are also different for different habitats. For example the rate of deposition of pollutants to forest vegetation is generally around twice that of deposition to short-vegetation. Forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a more shorter type of vegetation habitat types.

How are the average three year concentration and deposition values derived for each UK grid square?

In APIS background data are calculated on an annual basis but provided as rolling 3-year means. The 3-year mean data are ecosystem-specific providing two sets of values: (i) assuming moorland/short vegetation everywhere; (ii) assuming forest everywhere. Additionally grid average are provided as 3-year rolling means.

For Nitrogen deposition, Acid deposition and Ammonia concentration background values are calculated using the Concentration Based Estimated Deposition (CBED) methodology. CBED generates 5x5 km resolution gridded data of wet and dry deposition of sulphur, oxidised and reduced nitrogen, and base cations from measured concentrations of gases and particulate matter in air and measured concentrations of ions in precipitation.

These data are collected at sites in the UK Eutrophying and Acidifying Pollutants (UKEAP) network.  The site-based measurements are first interpolated to generate maps of concentrations for the UK.  The ion concentrations in precipitation are combined with an annual precipitation map from the UK Meteorological Office to generate values of wet deposition.  Gas and particulate matter concentration maps are combined with spatially distributed estimates of habitat-specific deposition velocities to generate dry deposition for 5 land cover categories: forest, moorland, grassland, arable and urban.  The deposition to the 5 land cover categories are combined, depending on the relative proportions of different land cover categories in the 5x5 km grid square, to generate values for grid square averaged deposition.

Ammonia concentrations are taken from a combination of the FRAME atmospheric chemical transport model and the annual measured concentrations from the UKEAP network, where the former generates the local scale variability that cannot be derived from the network measurement data on their own.

Significant inter-annual variations in deposition can occur due to the natural variability in annual weather patterns including precipitation which directly

influences wet deposition. Therefore, CBED deposition data used to calculate the exceedance of critical loads are therefore averaged over a three year period.

The Pollution Climate Mapping model (PCM) is used to produce background maps, 1x1 km grids of pollutant concentrations for SO2 and NOx. The annual mean background concentration maps for SO2 and NOx have been calculated by summing the contributions from: 

  • Distant sources (characterised by the rural background concentration)
  • Large point sources
  • Small point sources
  • Local area sources

The area source model has been calibrated using data from the national automatic monitoring networks. See the report for full methodology.

Is the N deposition provided for 5km grid square the total N deposition within that 5km grid square or an average over that 5km grid square?

It is the total deposition which is based on interpolating/krigging methods from a measured network to create a 5km grid. Some parts of the total (dry deposition NH3) are from modelled output.

Unit conversion

What is the meaning of 'keq' in keq/ha/year?

Keq stands for kiliequivalent. This helps to distinguish between the amount of a certain element within a whole molecule. For example, the nitrogen in ammonia, NH3.

The unit known as equivalent, eq (a keq is 1000 eq), refers to the molar equivalent of e.g. sulphur, oxidised and reduced nitrogen, as well as base cations. For example:

1 keq N ha-1 yr-1 is equal to 14 kg N ha-1 yr-1 and

1 keq S ha-1 yr-1 is equal to 16 kg S ha-1 yr-1.

When converting compounds the valency is important and is connected with the charge on the ion. For example: NH4+ or NO3- have a valency of 1.

For sulphur, the prevalent ion is sulphate SO42-, which has a double charge (valency). The full process is to convert kg to kmoles, then kmoles to keq. The 'equivalent' refers to the ionic charge on an ion. 1 kmole SO42- is 2 keq, (because of the double - charge) and 1 keq SO4 is 32/2 or 16 kg S.

Search by location

What are the dry deposition velocities used for the different gases for different habitats?

Deposition velocities are used in calculating deposition of nitrogen and sulphur. Different gases have different rates of deposition (and different deposition velocities) .

Deposition velocities are also different for different habitats. For example the rate of deposition of pollutants to forest vegetation is generally around twice that of deposition to short-vegetation. Forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a more shorter type of vegetation habitat types.

In the Search by Location tool, why is deposition different for deciduous woodland and neutral grassland in the same grid reference?

Reactive nitrogen deposits  to woodland/forest at a higher rate than to shorter vegetation types. This is because forests and woodland habitats have a higher aerodynamic roughness (e.g. leaves, branches etc) as opposed to a shorter type of vegetation habitat types and deposition to woodland habitats can be twice as that for short vegetation. So even at the same location different habitats can receive different depositions of pollutant.

APIS provides the appropriate deposition values for each of the main habitats using either short vegetation (labelled moorland) or tree (woodland) deposition velocities.

Site specific advice

Why are there data missing about Areas/Sites of Special Scientific Interest in some of the critical level/load datasets for download?

Some of the conservation agencies have provided information to National Vegetation Classification level for A/SSSIs (England primarily) and some have not. Where this level of detail is not available, the broad habitat classification has been used. In some cases, several critical loads may apply to habitats within this broad classification and as such, APIS advises to seek site specific advice from the relevant authority (eg conservation agency or site manager).

Trends

Does APIS have data about change in nitrogen deposition over time?

We have incorporated a feature in the Site Relevant Critical Loads tool which allows you to look at the trends in pollutant concentrations/deposition at protected nature conservation sites.  On the results pages of your chosen site there is a "tab" which labelled "Trends".  The data only go as far back as 2005 and displays the three-year average background data.

Sites (e.g.SACs/SPAs & SSSIs)
Critical loads

Why does APIS say to seek site specific advice?

Critical loads and levels have been established for many habitats and are based on the best available information. However, for some habitats a variety of site specific factors can influence how much of certain air pollutant concentrations or deposition might presents a risk to their function. As such, there may be insufficient information to assign a critical level or load to all types of habitat on that specific site. In these cases, APIS advises to seek site specific information from the relevant authority (eg conservation agency or site manager).

Why is there no critical load assigned for some features?

Critical loads have been established for many habitats and are based on the best available information. As such, there may be insufficient information to assign a critical load to all types of habitat on that specific site. However, linkages have been applied where possible. This also sometimes means that there is more than one critical load for a particular habitat. Where no comparable critical load is given, it is advised to seek site specific information from the relevant authority (e.g. conservation agency or site manager).

 

You can see examples of EUNIS habitat classes their critical loads in the habitats table.

There are two sets of values CLmaxS, CLminN and CLmaxN for each SAC or SSSI i.e. minCLmaxN and maxCLmaxN. Which should be used here? Should both sets of values be assessed and, if so, how should the results be reported?

The acidity critical loads values are based on a 1km grid for the UK. Consequently, for sites that are larger than 1 km2 will have many critical load grid squares covering the site. For this reason we give a maximum and minimum set of critical loads. For initial assessments, the minimum set of critical levels should be used as this follows the precautionary approach.

Are freshwater systems (eg flowing water, mesotrophic and eutrophic waters) sensitive to acid and nitrogen deposition?

Freshwater habitats have a complex interaction with air pollution and as such, APIS often states to seek site specific advice. This is because some freshwater habitat types may be sensitive to air pollution. You should use the relevant general freshwater type and pollutant combination for your assessment. For acidification there are pages on rivers  - and standing water/canals.
 
The APIS Habitat/Pollutant impacts tab can help for understanding the evidence for effects from air pollution types on different freshwater systems as well as other habitats. For example, the standing water and canals page for nitrogen deposition describes the nuances of nitrogen:phosphorus relationships and why it is difficult to then establish a critical load for all situations:

"A critical load cannot be given for nitrogen, as quantitative relationships between biology and nitrogen concentrations are poorly understood. The nitrogen to phosphorus ratio can be important, with a molar ratio of around 16:1 (7:1 by weight) being the threshold between N- and P-limitation (Wetzel 2001). Impacts could be assessed by deviation from a 'natural' ratio for an individual site."

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Why are there multiple critical load graphs for the same interest features at a particular site especially for dune habitats?

Some habitats have been linked/matched to more than one nitrogen critical load and local site knowledge should be used to set the right one. For (most) sand dune habitats they can have a critical load associated with acid or calcareous soils, hence they have different critical loads.

Site specific advice should be sought from the relevant authority where there is doubt in which critical load to use.

Critical levels

How do you apply the appropriate ammonia critical level to a vegetation type. For example, for vegetation types such as peatland and woodland would apply the 1ug it would mainly contain lower plants?

This is both a both habitat and site specific consideration.  For bog habitats where lower plants are integral to the habitat function, the lower (1ugm-3) critical level for ammonia is relevant. This more stringent critical level will also be relevant to the woodland if lichen/bryophyte interest is 'an integral part' of the woodland. For protected sites the Site Relevant Critical Loads tool can help as it gives the ammonia critical level for features.

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Acidity

There are two sets of values CLmaxS, CLminN and CLmaxN for each SAC or SSSI i.e. minCLmaxN and maxCLmaxN. Which should be used here? Should both sets of values be assessed and, if so, how should the results be reported?

The acidity critical loads values are based on a 1km grid for the UK. Consequently, for sites that are larger than 1 km2 will have many critical load grid squares covering the site. For this reason we give a maximum and minimum set of critical loads. For initial assessments, the minimum set of critical levels should be used as this follows the precautionary approach.

Ecological Impacts

How do you apply the appropriate ammonia critical level to a vegetation type. For example, for vegetation types such as peatland and woodland would apply the 1ug it would mainly contain lower plants?

This is both a both habitat and site specific consideration.  For bog habitats where lower plants are integral to the habitat function, the lower (1ugm-3) critical level for ammonia is relevant. This more stringent critical level will also be relevant to the woodland if lichen/bryophyte interest is 'an integral part' of the woodland. For protected sites the Site Relevant Critical Loads tool can help as it gives the ammonia critical level for features.

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Are freshwater systems (eg flowing water, mesotrophic and eutrophic waters) sensitive to acid and nitrogen deposition?

Freshwater habitats have a complex interaction with air pollution and as such, APIS often states to seek site specific advice. This is because some freshwater habitat types may be sensitive to air pollution. You should use the relevant general freshwater type and pollutant combination for your assessment. For acidification there are pages on rivers  - and standing water/canals.
 
The APIS Habitat/Pollutant impacts tab can help for understanding the evidence for effects from air pollution types on different freshwater systems as well as other habitats. For example, the standing water and canals page for nitrogen deposition describes the nuances of nitrogen:phosphorus relationships and why it is difficult to then establish a critical load for all situations:

"A critical load cannot be given for nitrogen, as quantitative relationships between biology and nitrogen concentrations are poorly understood. The nitrogen to phosphorus ratio can be important, with a molar ratio of around 16:1 (7:1 by weight) being the threshold between N- and P-limitation (Wetzel 2001). Impacts could be assessed by deviation from a 'natural' ratio for an individual site."

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Habitats protected sites

How can I get critical loads for Local wildlife sites?

APIS has information available about designated sites that are explicitly covered by the country nature conservation bodies (eg European Sites and Areas/Sites of Special Scientific Interest). Currently APIS does not include local wildlife sites as this information is held by the local authority or site manager.

However, you can use the habitats table showing critical loads to use in risk assessment.

Alternatively, you might consider using the habitat and critical load/level data available at the link .  Professional judgment can be used to approximate the local wildlife site habitat with habitats in this dataset to determine the critical levels and loads to use in assessment.

Are freshwater systems (eg flowing water, mesotrophic and eutrophic waters) sensitive to acid and nitrogen deposition?

Freshwater habitats have a complex interaction with air pollution and as such, APIS often states to seek site specific advice. This is because some freshwater habitat types may be sensitive to air pollution. You should use the relevant general freshwater type and pollutant combination for your assessment. For acidification there are pages on rivers  - and standing water/canals.
 
The APIS Habitat/Pollutant impacts tab can help for understanding the evidence for effects from air pollution types on different freshwater systems as well as other habitats. For example, the standing water and canals page for nitrogen deposition describes the nuances of nitrogen:phosphorus relationships and why it is difficult to then establish a critical load for all situations:

"A critical load cannot be given for nitrogen, as quantitative relationships between biology and nitrogen concentrations are poorly understood. The nitrogen to phosphorus ratio can be important, with a molar ratio of around 16:1 (7:1 by weight) being the threshold between N- and P-limitation (Wetzel 2001). Impacts could be assessed by deviation from a 'natural' ratio for an individual site."

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Why are there multiple critical load graphs for the same interest features at a particular site especially for dune habitats?

Some habitats have been linked/matched to more than one nitrogen critical load and local site knowledge should be used to set the right one. For (most) sand dune habitats they can have a critical load associated with acid or calcareous soils, hence they have different critical loads.

Site specific advice should be sought from the relevant authority where there is doubt in which critical load to use.

Site specific advice

How do you apply the appropriate ammonia critical level to a vegetation type. For example, for vegetation types such as peatland and woodland would apply the 1ug it would mainly contain lower plants?

This is both a both habitat and site specific consideration.  For bog habitats where lower plants are integral to the habitat function, the lower (1ugm-3) critical level for ammonia is relevant. This more stringent critical level will also be relevant to the woodland if lichen/bryophyte interest is 'an integral part' of the woodland. For protected sites the Site Relevant Critical Loads tool can help as it gives the ammonia critical level for features.

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Why does APIS say to seek site specific advice?

Critical loads and levels have been established for many habitats and are based on the best available information. However, for some habitats a variety of site specific factors can influence how much of certain air pollutant concentrations or deposition might presents a risk to their function. As such, there may be insufficient information to assign a critical level or load to all types of habitat on that specific site. In these cases, APIS advises to seek site specific information from the relevant authority (eg conservation agency or site manager).

Why is there no critical load assigned for some features?

Critical loads have been established for many habitats and are based on the best available information. As such, there may be insufficient information to assign a critical load to all types of habitat on that specific site. However, linkages have been applied where possible. This also sometimes means that there is more than one critical load for a particular habitat. Where no comparable critical load is given, it is advised to seek site specific information from the relevant authority (e.g. conservation agency or site manager).

 

You can see examples of EUNIS habitat classes their critical loads in the habitats table.

Are freshwater systems (eg flowing water, mesotrophic and eutrophic waters) sensitive to acid and nitrogen deposition?

Freshwater habitats have a complex interaction with air pollution and as such, APIS often states to seek site specific advice. This is because some freshwater habitat types may be sensitive to air pollution. You should use the relevant general freshwater type and pollutant combination for your assessment. For acidification there are pages on rivers  - and standing water/canals.
 
The APIS Habitat/Pollutant impacts tab can help for understanding the evidence for effects from air pollution types on different freshwater systems as well as other habitats. For example, the standing water and canals page for nitrogen deposition describes the nuances of nitrogen:phosphorus relationships and why it is difficult to then establish a critical load for all situations:

"A critical load cannot be given for nitrogen, as quantitative relationships between biology and nitrogen concentrations are poorly understood. The nitrogen to phosphorus ratio can be important, with a molar ratio of around 16:1 (7:1 by weight) being the threshold between N- and P-limitation (Wetzel 2001). Impacts could be assessed by deviation from a 'natural' ratio for an individual site."

If in doubt, seek site specific advice from the relevant authority (eg conservation agency or site manager).

Why are there multiple critical load graphs for the same interest features at a particular site especially for dune habitats?

Some habitats have been linked/matched to more than one nitrogen critical load and local site knowledge should be used to set the right one. For (most) sand dune habitats they can have a critical load associated with acid or calcareous soils, hence they have different critical loads.

Site specific advice should be sought from the relevant authority where there is doubt in which critical load to use.

Ecosystem responses
Critical levels

Does APIS hold data about lichen sensitivity to nitrogen oxides?

Lichen are recognised as being sensitive to concentrations in air of pollutants (nitrogen oxide and ammonia) as well as their deposition. APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses).

There are critical levels set for lichens for some pollutants (SO2 and ammonia) to quantify when the pollutant concentration in air is expected to affect lichens. Critical loads relating to effects from nutrient nitrogen deposition have not been outlined for individual lichen species at this time.

In a brief search of the APIS website for "lichen" and "deposition", the following page was identified (http://www.apis.ac.uk/node/1027 ). It indicates a proxy critical load for woodland could be helpful for lichen growing on trees. A similar approach might be taken for lichen growing on the ground or in wet conditions (eg assign critical load from the habitat the lichen is growing in - bog, heathland or grassland).

Biomonitoring

How can I tell if a lichen indicates good or bad air quality?

APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses). You can also check out the lichen app pages and lichen identifier guide to find out more on the impacts of nitrogen deposition to lichens.

Ecological Impacts

Does APIS hold data about lichen sensitivity to nitrogen oxides?

Lichen are recognised as being sensitive to concentrations in air of pollutants (nitrogen oxide and ammonia) as well as their deposition. APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses).

There are critical levels set for lichens for some pollutants (SO2 and ammonia) to quantify when the pollutant concentration in air is expected to affect lichens. Critical loads relating to effects from nutrient nitrogen deposition have not been outlined for individual lichen species at this time.

In a brief search of the APIS website for "lichen" and "deposition", the following page was identified (http://www.apis.ac.uk/node/1027 ). It indicates a proxy critical load for woodland could be helpful for lichen growing on trees. A similar approach might be taken for lichen growing on the ground or in wet conditions (eg assign critical load from the habitat the lichen is growing in - bog, heathland or grassland).

Lichen app

How can I tell if a lichen indicates good or bad air quality?

APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses). You can also check out the lichen app pages and lichen identifier guide to find out more on the impacts of nitrogen deposition to lichens.

Lichens & bryophytes

How can I tell if a lichen indicates good or bad air quality?

APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses). You can also check out the lichen app pages and lichen identifier guide to find out more on the impacts of nitrogen deposition to lichens.

Does APIS hold data about lichen sensitivity to nitrogen oxides?

Lichen are recognised as being sensitive to concentrations in air of pollutants (nitrogen oxide and ammonia) as well as their deposition. APIS has a dedicated page for impacts of air pollution on lichens and bryophytes (mosses).

There are critical levels set for lichens for some pollutants (SO2 and ammonia) to quantify when the pollutant concentration in air is expected to affect lichens. Critical loads relating to effects from nutrient nitrogen deposition have not been outlined for individual lichen species at this time.

In a brief search of the APIS website for "lichen" and "deposition", the following page was identified (http://www.apis.ac.uk/node/1027 ). It indicates a proxy critical load for woodland could be helpful for lichen growing on trees. A similar approach might be taken for lichen growing on the ground or in wet conditions (eg assign critical load from the habitat the lichen is growing in - bog, heathland or grassland).

APIS webiste (navigating, reporting bugs, update logs)
Background data

How can I set alerts to ensure that I am kept up to date with any revisions to the background/critical load information?

Currently there is no ‘Newsletter’ for APIS. Background data is updated yearly around March of every year. We will announce any updates on the homepage ‘News’ section and changes are also recorded in the APIS update log.

Bugs, errors & contacting us

How can I provide information to refine an entry on APIS or highlight errors?

Use the APIS contact form to highlight any bugs, revisions required or to provide suggestions. If requesting a site specific change, provide the specific evidence through the contact form with a URL. The request will need to be supported by the conservation body or agency responsible for the site. The change will be considered by the APIS Steering Group and updated accordingly.

Why won’t my grid reference work in the Search by Location Tool?

To use the APIS location tool, the location can be expressed in two ways: Either as a 6 figure grid reference - NO095275 or through an OS Easting|Northing  e.g. 309525,727549. (don’t leave a space between the comma and the next number).

How can I report broken links on the APIS website?

Use the APIS contact form to highlight any bugs, revisions required or to provide suggestions.

If reporting a broken link, please provide the specific URL for the APIS page and details of the link in that page that is broken.

Thank you for your help to make APIS better for its users.

Get involved

How can I get more involved in UK air pollution work?

Each country conservation agency and regulators have their own websites if you are interested in
Civil Service jobs will hold advertisements for conservation bodies and regulators in England that use biomonitoring -
• Northern Ireland – Northern Ireland Environment Agency and Department of Agriculture, Environment and Rural Affairs
• Scotland – Scottish Natural Heritage Information Hub
• Wales – Natural Resources Wales Evidence and Data
• Defra’s UK-Air has links to research priorities

There are also research institutions such as UKCEH (UK Centre for Ecology and Hydrology), Ricardo AEA and Rothamsted Research that might be interested in a biomonitoring project and your skills.

Update log

How can I set alerts to ensure that I am kept up to date with any revisions to the background/critical load information?

Currently there is no ‘Newsletter’ for APIS. Background data is updated yearly around March of every year. We will announce any updates on the homepage ‘News’ section and changes are also recorded in the APIS update log.

Search by location

Why won’t my grid reference work in the Search by Location Tool?

To use the APIS location tool, the location can be expressed in two ways: Either as a 6 figure grid reference - NO095275 or through an OS Easting|Northing  e.g. 309525,727549. (don’t leave a space between the comma and the next number).