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 mosses, bryophytes and liverworts. 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 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: Trends in critical load and critical level exceedances in the UK.
Figure A7: Area of land in England exposed to damaging levels of ammonia (NH3) in the atmosphere, 2009-2011 to 2017-2019
Table A7: Area of land in England exposed to damaging levels of ammonia (NH3) in the atmosphere, 2009-2011 to 2017-2019
Trend description for A7
The percentage of land area exposed to concentrations of NH3 that exceed critical levels (1 μg per m3) remained relatively constant at about 90.2% between the 3-year moving time periods 2009 to 2011 and 2012 to 2014. It then increased slightly over the next 5 years to reach 94% in the most recent 3-year period reported in this indicator (2017 to 2019).
Assessment of change
The area of land exposed to damaging levels of NH3 in the atmosphere increased slightly (a deterioration) over the short-term assessment period. The time series is not yet long enough to make an assessment over the medium and long-term time periods.
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 2 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||Subcomponent||Period||Date range||Percentage change||Smoothing function||Assessment of change|
|A7||None||Short term||2012-2014 to 2017-2019||4.21||moving average data||Deterioration|
|A7||None||Medium term||N/A||N/A||N/A||Not assessed|
|A7||None||Long term||N/A||N/A||N/A||Not assessed|
Note that percentage change refers to the difference seen from the first to last 3-year moving average in the specified date range.