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Air Quality

Particulate (PM₁₀) Concentrations: 1993-2004

Particulate pollution can harm the human respiratory and cardiovascular systems, and is linked to asthma and mortality. Smaller particles are the most damaging and current targets focus on particles less than 10µm in diameter (PM ₁₀).

The greatest source of PM ₁₀ is combustion. In particular, road transport and domestic sources accounted for around 40% of UK emissions of PM ₁₀ in 2003.3 Between 1990 and 2003, UK emissions of PM ₁₀ fell by 51%. ³

The Air Quality Strategy4 objectives for PM ₁₀ come in two stages. Stage 1 (to be met by the end of 2004): a 24-hour mean of 50µg/m ³ not to be exceeded more than 35 times a year, and an annual mean of 40µg/m ³. Stage 2 (to be met by the end of 2010): a 24-hour mean of 50µg/m ³ not to be exceeded more than seven times a year, and an annual mean of 18µg/m ³. Stage 1 objectives were met at all automatic monitoring sites in 2004.

SOURCE: UK NATIONAL AIR QUALITY ARCHIVE

High concentrations of nitrogen dioxide (NO ₂) can affect human health, particularly by causing inflammation of the airways. Ecosystem health is also damaged by NO ₂ by reducing plant growth, contributing to acid deposition and promoting the formation of ground level ozone.

All combustion processes in air produce oxides of nitrogen (NO _x). Road transport accounted for 40% of all UK NO _x emissions in 2003; this contribution is greatly increased in urban areas. Between 1990 and 2003, UK emissions of NO _x decreased by 44% ³ due to the installation of catalytic converters in vehicles.

The Air Quality Strategy ⁴ objectives for NO ₂ (to be met by the end of 2005) are (1) an annual mean of 40µg/m ³ and (2) an hourly mean of 200µg/m ³ not to be exceeded more than 18 times a year. In 2004, the first objective was not met at two of the eight automatic monitoring sites in Scotland - Glasgow City Chambers and Glasgow Kerbside. The second objective was met at all automatic monitoring sites.

SOURCE: UK NATIONAL AIR QUALITY ARCHIVE

Carbon monoxide (CO) is a gas formed by the incomplete combustion of carbon-based fuels. The greatest threat to human health from exposure to CO is the formation of carboxyhaemoglobin. This reduces the capacity of the blood to carry oxygen resulting in drowsiness, headaches, and in severe cases unconsciousness and death.

The Air Quality Strategy ⁴ ( AQS) objective for CO is a maximum concentration of 10mg/m ³ measured as an 8-hour running mean. There are no instances of this limit being exceeded since 1992.

The main outdoor source of carbon monoxide is currently road transport, in particular petrol-fuelled vehicles, which in 2003 accounted for 49% of UK emissions.3 Between 1990 and 2003, UK emissions of CO from road transport have fallen by 75%, a decline attributed to the installation of catalytic converters in vehicles.

SOURCE: UK NATIONAL AIR QUALITY ARCHIVE

Ozone in the stratosphere forms a layer that protects the earth against harmful ultra-violet radiation, but tropospheric (ground level) ozone is a damaging oxidant. Exposure to high ozone concentrations can cause respiratory damage, and affects vegetation by damaging leaves and reducing yields.

Ozone is formed by a slow, complicated series of reactions from other pollutants that may be blown over from Europe. The most important man-made precursors are nitrogen oxides and volatile organic compounds ( VOCs) produced by road transport, industrial processes and solvent use. Ozone concentrations tend to be lower in urban areas where it is converted to nitrogen dioxide by reacting with nitrogen oxides.

The Air Quality Strategy4 objective for ground level ozone (to be met by 2005) is for the maximum daily concentration (measured as an 8-hour running mean) of 100µg/m ³ not to be exceeded more than 10 times a year. ⁹ In 2004, this objective was not met at Strath Vaich (29 exceedences).

SOURCE: UK NATIONAL AIR QUALITY ARCHIVE

The predominant source of atmospheric sulphur dioxide (SO ₂) is the combustion of sulphur-containing fossil fuels, mainly coal and heavy oils. Annual urban SO ₂ levels have fallen by around 75% since the 1956 Clean Air Act was introduced to combat smog.

High SO ₂ levels over a short period of time are important as such incidents may cause respiratory difficulties. The Air Quality Strategy ⁴ objective for SO ₂ stipulates that a 15-minute mean of 266µg/m ³ should not be exceeded more than 35 times a year (to be met by the end of 2005). Grangemouth failed to meet this objective in 2004; the remaining three sites all passed (there were two exceedences in Aberdeen in 2004).

In cold weather, SO ₂ can contribute to acidification that damages vegetation and ecosystems. The AQS objective for ecosystem protection, a winter (1 October-31 March) mean of 20µg/m ³, is currently met at all Scottish automatic monitoring stations.

SOURCE: UK NATIONAL AIR QUALITY ARCHIVE

Annual emissions (thousand tonnes)

Sulphur dioxide (SO ₂) and oxides of nitrogen (NOx) affect human health through respiratory damage, and ecosystem health through acidification. SO ₂ and NOx are released into the atmosphere through the combustion of fossil fuels. In 2003, large combustion plants ( LCPs) accounted for 75% of the SO ₂ emissions and 24% of NOx emissions in the UK. ³

The revised ECLCP Directive (2001/80/ EC) called for a 60% reduction in SO ₂ emissions by 2003 and a 30% reduction in NOx emissions by 1998, from a 1980 baseline. By 2002, UK emissions for SO ₂ and NOx were 78% and 64% respectively below 1980 levels. ³ In Scotland, SO ₂ emissions from the electricity supply industry fell between 1996 and 1999, but rose in 2000. This was due to the increased use of coal-fired power stations, necessary to offset the reduced capacity of the nuclear sector because of refurbishment work at certain plants.

Acid deposition is a transboundary problem. In 1994, it was estimated that 81% of sulphur deposited in Scotland was emitted in other parts of Europe. ¹⁵ Similarly, most Scottish emissions are deposited elsewhere.

SOURCE: SCOTTISH ENVIRONMENT PROTECTION AGENCY

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