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B5a. Air pollution

Type: Pressure Indicator

Indicator Description

The air pollutants sulphur dioxide, nitrogen oxides and ammonia can contribute to acidification, and nitrogen oxides and ammonia can contribute to terrestrial eutrophication. These pollutants arise mainly from burning fossil fuels and from livestock waste. Around a third of UK land area is sensitive to acidification, and a third to eutrophication (with some areas sensitive to both). Critical loads are thresholds for pollutant load above which significant harmful effects may occur on sensitive habitats, so statistics on critical load exceedance indicate the risk of damage.

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Summary

The area of sensitive UK habitats that exceeds the critical load for acidification has continued to decline since 1996[1], but there has been less change in the area that exceeds the critical load for eutrophication. Acid deposition exceeded critical load in 43% of sensitive habitats in 2015, and nitrogen deposition exceeded critical load in 62% of sensitive habitats in 2015.

Critical loads are thresholds for the deposition of pollutants causing acidification and/or eutrophication above which significant harmful effects on sensitive UK habitats may occur.  Approximately 78,000 km2 of UK terrestrial habitats is sensitive to acid deposition.  About 73,000 km2 is sensitive to eutrophication; much of this is sensitive to both.

In 1996, acid deposition exceeded critical loads in 73% of the area of sensitive habitats.  This declined to 43% in 2015. There has been a slight decrease in the area affected over the short term, since 2010, when the figure was 47%.

In 2015, nitrogen deposition exceeded critical loads in 62% of sensitive habitats.  This was a decrease from a level of 75% in 1996.  However there was little change in the short term.

Based on these figures the habitat areas at risk from acid and nitrogen deposition has declined over the long term (1996 to 2015), however, reducing deposition below the critical loads does not necessarily mean that ecosystems have recovered, as there can be a time-lags before the chemical environment and the flora and fauna recover.

Figure B5ai.  Area of sensitive UK habitats exceeding critical loads for acidification and eutrophication, 1996 to 20151

A two column bar chart showing the percentage of sensitive habitat area for acidity and nutrient nitrogen between 1996 and 2015.  The chart shows the area of sensitive UK habitats that exceeds the critical load for acidification has continued to decline since 1996, but there has been less change in the area that exceeds the critical load for eutrophication.

Notes:

  1. Each column represents critical load exceedances based on a 3-year average of deposition data to reduce year-to-year variability.
  2. Since 2002, nitric acid has been included in the estimates of nitrogen deposition, and since 2003 aerosol deposition loads of sulphate, nitrate and ammonium have also been included.  This additional deposition led to some increases in critical load exceedance compared with earlier periods.
  3. There are a few inconsistencies between years due to changes in methods used to derive deposition estimates, and some minor alterations to the acidity critical loads. This information should be taken into account when interpreting the trends results.

Source: Centre for Ecology & Hydrology.

Assessment of change in area of sensitive habitat exceeding critical loads

 

Long term

Short term

Latest year

Area affected by acidity


1996–2015


2010-2015

Decreased (2015)

Area affected by nitrogen


1996–2015


2010-2015

Decreased (2015)

Note: Long- and short-term assessments are based on a 3% rule of thumb. Where possible, the base years for these assessments use a 3-year average. See Assessing Indicators.

[1] For ease of reference, time periods are usually referred to using the middle year of the 3 years used to calculate the mean.  This example “1996” refers to the time period 1995 to 1997. In figure B5ai “1996 to 2015” refers to the time period 1995–1997 to 2014–16.

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Downloads

Download the Fiche, Datasheet and Technical background document from the JNCC Resource Hub

Last updated:  September 2019

Latest data available: 2015 (2014 – 2016)

 

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Categories:

UK Biodiversity Indicators 2019

Published: .

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