A7: Area of land exposed to damaging levels of ammonia (NH3) in the atmosphere

Short Description

This indicator tracks changes in the amount of land area affected by damaging levels of ammonia (NH3) in the air. Excess NH3 in the atmosphere leads to direct toxic effects on vegetation, with very low concentrations causing damage to the leaves and surfaces of sensitive plant species such as lichens and bryophytes (mosses and liverworts) an integral part of many habitats. Agriculture is the main source of NH3 emissions to the atmosphere.

This indicator is a measure of pressure on sensitive plant species from air pollution. It shows the percentage of land area where interpolated measurements of ground-level air exceed the lower critical level threshold for NH3 of 1 microgram per cubic metre (μg per m3).

Readiness and links to data

Assessments of damaging levels of ammonia in the atmosphere are undertaken and published annually using 3-year moving average data at UK Air Information Resource: Critical load and critical level exceedances in the UK.

Indicator components

Figure A7: Area of land in England exposed to damaging levels of ammonia (NH3) in the atmosphere, 2002-2004 to 2019-2021

Source

UK Centre for Ecology & Hydrology, Air Pollution Trends Report 2023: Critical Load and Critical Level exceedances in the UK

Unit of Measurement

Percentage of land area exceeding critical levels

Footnotes

Data are presented as 3-year moving average time periods. A 3-year moving average is used to smooth out inter-annual variability due to the influence of weather on atmospheric chemistry.

Subsequent back casting of the data using a new methodology introduced in advance of the 2023 update has resulted in a time-series that now extends back to the 3-year period 2002 to 2004. These changes also mean that the chart presented here cannot be directly compared to charts presented in publications of this indicator prior to 2023.

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Table A7: Area of land in England exposed to damaging levels of ammonia (NH3) in the atmosphere, 2002-2004 to 2019-2021

Year	Value
2002-2004	83.60
2003-2005	83.50
2004-2006	82.50
2005-2007	84.50
2006-2008	84.40
2007-2009	84.60
2008-2010	84.50
2009-2011	88.70
2010-2012	87.10
2011-2013	87.20
2012-2014	83.30
2013-2015	86.40
2014-2016	87.60
2015-2017	88.60
2016-2018	90.60
2017-2019	92.40
2018-2020	92.50
2019-2021	90.50

Source

UK Centre for Ecology & Hydrology, Air Pollution Trends Report 2023: Critical Load and Critical Level exceedances in the UK

Unit of Measurement

Percentage of land area exceeding critical levels

Footnotes

Data are presented as 3-year moving average time periods. A 3-year moving average is used to smooth out inter-annual variability due to the influence of weather on atmospheric chemistry.

Subsequent back casting of the data using a new methodology introduced in advance of the 2023 update has resulted in a time-series that now extends back to the 3-year period 2002 to 2004. These changes also mean that the chart presented here cannot be directly compared to charts presented in publications of this indicator prior to 2023.

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Trend description for A7

Overall, the percentage of land area exposed to concentrations of NH3 that exceed critical levels (1 μg per m3) has increased by 8% between the 3-year moving time periods 2002-2004 and 2019-2021, although there has been a slight decrease in the most recent data point.

Assessment of change

The area of land exposed to damaging levels of NH3 in the atmosphere has increased (a deterioration) over the short and long-term assessment periods and shown little or no change over the medium-term assessment period.

Change since 2018 has also been assessed. Little or no change was observed for exceedance of damaging levels of NH3 in the atmosphere since 2018. However, this result is based on only 4 data points so should be considered as indicative and not evidence of a clear trend.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.

Table A7: Assessment of change

Component	Period	Date range	Percentage change	Smoothing function	Assessment of change
A7	Short term	2014-2016 to 2019-2021	3.31	Moving average data	Deterioration
A7	Medium term	2009-2011 to 2019-2021	2.03	Moving average data	Little or no change
A7	Long term	2002-2004 to 2019-2021	8.25	Moving average data	Deterioration

Note that percentage change refers to the difference seen from the first to last 3-year moving average in the specified date range.

Indicator Metadata

Headline indicator status: Not applicable
Primary goal in the 25 Year Environment Plan: Clean air
Relevant goal(s) in the 25 Year Environment Plan: Clean air; Thriving plants and wildlife
Relevant target(s) in the 25 Year Environment Plan: Meeting legally binding targets to reduce emissions of five damaging air pollutants; Restoring 75% of our one million hectares of terrestrial and freshwater protected sites to favourable condition, securing their wildlife value for the long term; Creating or restoring 500,000 hectares of wildlife-rich habitat outside the protected site network, focusing on priority habitats as part of a wider set of land management changes providing extensive benefits
Position in the natural capital framework: Pressure on natural capital assets
Related reporting commitments: International Collaborative Partnership reporting under United Nations Economic Commission for Europe’s Working Group on Effects
Geographical Scope: England
Status of indicator development: Final
First Reported: 2019
Last Updated: 2024
Latest Data: 2021