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 2020-2022
Table A7: Area of land in England exposed to damaging levels of ammonia (NH3) in the atmosphere, 2002-2004 to 2020-2022
| Year | Value |
|---|---|
| 2002-2004 | 83.80 |
| 2003-2005 | 83.90 |
| 2004-2006 | 83.30 |
| 2005-2007 | 85.40 |
| 2006-2008 | 85.40 |
| 2007-2009 | 86.00 |
| 2008-2010 | 85.50 |
| 2009-2011 | 89.30 |
| 2010-2012 | 87.40 |
| 2011-2013 | 87.80 |
| 2012-2014 | 84.00 |
| 2013-2015 | 87.20 |
| 2014-2016 | 88.40 |
| 2015-2017 | 89.80 |
| 2016-2018 | 91.40 |
| 2017-2019 | 91.50 |
| 2018-2020 | 90.80 |
| 2019-2021 | 85.30 |
| 2020-2022 | 80.60 |
Trend description for A7
Overall, the percentage of land area exposed to concentrations of NH3 that exceed critical levels (1 μg per m3) has decreased by 3.2 percentage points between the 3-year moving average time periods 2002-2004 and 2020-2022. The percentage of land area has shown a decreasing trend since reaching its peak in the time series of 91.5% in 2017-2019.
Assessment of change
The area of land exposed to damaging levels of NH3 in the atmosphere has decreased (an improvement) over the short-, medium- and long-term assessment periods.
Change since 2018 has also been assessed. A decrease (improvement) was observed for exceedance of damaging levels of NH3 in the atmosphere since the 2016-2018 period. However, this result is based on only 5 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 | 2015-2017 to 2020-2022 | -10.24 | Moving average data | Improvement |
| A7 | Medium term | 2010-2012 to 2020-2022 | -7.78 | Moving average data | Improvement |
| A7 | Long term | 2002-2004 to 2020-2022 | -3.82 | Moving average data | Improvement |
Note that percentage change refers to the difference seen from the first to last 3-year moving average in the specified date range.