After 40-year decrease, figures show rise in UK acid rain pollution

The UK Government has revealed a year-on-year increase in the amount of sulphur dioxide emissions, which reverses a 40-year downward trend.

For the first time since the Seventies, official statistics show a small increase in the emissions of the sulphur dioxide of 2.3 per cent between 2009 and 2010.

The Defra report blamed the rise on a harsher winter and resulting increases in fuel consumption for heating and electricity generation.

However, the release pointed out that emissions of sulphur dioxide had still fallen by 89 per cent between 1990 and 2010, from 3.7 to 0.41 million tonnes.

The main source of sulphur dioxide (SO2) emissions is from combustion in energy production and transformation (58 per cent in 2010), followed by combustion in manufacturing industries (18 per cent in 2010).

It is these sources that have been the strongest drivers for the long term trend of falling emissions, by switching from coal to gas and improved efficiency.

Sulphur dioxide triggers chemical reactions in the atmosphere, which creates acidic air pollution which can cause harm to vegetation and buildings, including as acid-rain.

The report reveals the UK is still ahead of meeting current international targets to reduce emissions of sulphur dioxide and are 31 per cent below the lowest goal.

Other key findings of today's release, include:

* The UK has met current international targets to reduce total emissions by 2010 of four air pollutants that cause harm to people’s health and to the natural environment.

* Emissions of nitrogen oxides have fallen by 62 per cent between 1990 and 2010, and fell by 3 per cent between 2009 and 2010. Emissions in 2010 were 5 per cent below the lowest international target for the UK.

* Emissions of non-methane volatile organic compounds have fallen by 71 per cent between 1990 and 2010, and fell by 4 per cent between 2009 and 2010. Emissions in 2010 were 34 per cent below the international target for the UK.

* Emissions of ammonia have fallen by 21 per cent between 1990 and 2010, but increased by 0.5 per cent between 2009 and 2010. Emissions in 2010 were 4 per cent below the international target for the UK.

Today's report explains the many sources of air pollution, including power stations, traffic, household heating, agriculture and industrial processes.

The National Atmospheric Emissions Inventory (NAEI) provides estimates of the amount and the type of pollutants that are emitted to the air each year from all UK sources. These are estimated to help to find ways of reducing the impact of human activities and the resulting air pollutants on the environment and health.

Some air pollutants directly affect the population or our environment because they are harmful chemicals (such as nitrogen dioxide from nitrogen oxides and some Non Methane Volatile Organic Compounds (NMVOCs)) and others because they can react in the environment to produce harmful chemicals.

Other pollutants or pollutant combinations upset the natural balance of acidity and nitrogen in the environment (such as sulphur dioxide, nitrogen oxides and ammonia) and can for example damage sensitive environments and buildings through acid rain.

The Defra National Statistics Release covers UK emissions of:

* sulphur dioxide (SO2)

* nitrogen oxides (NOx);

* non-methane volatile organic compounds (NMVOCs); and

* ammonia (NH3).

These four pollutants are primarily responsible for:

 acidification (SO2, NOx and NH3) - where chemical reactions involving air pollutants create acidic compounds which can cause harm to vegetation and buildings (including as acid-rain);

 eutrophication (NOx and NH3) - where the nitrogen can be deposited in soils or in rivers and lakes through rain and affects the nutrient levels and diversity of species in sensitive environments, for example encouraging algae growth in lakes and water courses.

 ground-level ozone (NOx and NMVOCs) – where chemical reactions involving air pollutants create the toxic gas ozone (O3) which can affect people’s health and can damage wild plants, crops, forests and some materials.

All four pollutants can also react in the atmosphere to form secondary particulate matter (PM). PM emissions can adversely impact human health, with chronic exposure to PM contributing to the risk of developing cardiovascular and respiratory diseases.

There are two main international agreements on air pollution emissions, both of which have 2010 as the target year:

 the National Emission Ceilings Directive (NECD) - sets ceilings for each EU Member State for emissions of sulphur dioxide, nitrogen oxides, non-methane volatile organic compounds (NMVOCs), and ammonia.

 the Gothenburg Protocol under the Convention on Long Range Transboundary Air Pollution (CLRTAP) - sets similar or identical UK emissions ceilings for the same pollutants.

Reductions in air pollutant emissions are achieved by for example changes in fuel use (such as switching from coal to gas power stations), through reducing fuel use, through changes to industrial processes, through pollutant capture or conversion (for example catalytic convertors on vehicles), and through legal restrictions.

Changes in behaviour such as making more sustainable transport choices also contribute to emissions reductions. Behaviour and hence the level of emissions can be also influenced by changes in fuel price and the wider economic situation.

The NAEI is used to monitor emissions against the international targets, and the UK figures are reported annually to the European Commission via the European Environment Agency.

The statistics released today compare the UK emissions against the international targets.

Some pollutants, referred to as greenhouse gases (such as carbon dioxide) may have little direct effect on health, but can contribute to changing global conditions and potentially give rise to dramatic changes in climate and sea level. Trends for greenhouse gases are produced by the NAEI, and are published separately by the Department for Energy and Climate Change.

The report notes that the mass of the emissions for the different pollutants should not be compared as their effects on health and the environment are very different.

Whilst overall reductions in air emissions may signify reductions in potential harm to human health or to the natural environment, the way the pollutant is emitted is also important. Emissions from high chimneys (for example power stations) will not affect air quality (concentrations of pollutants) as much as the same quantity of emissions released at ground level such as from cars and buses.

This is because pollutants emitted close to the ground do not generally get dispersed as well as pollutants emitted further from the ground.

It is not possible, except for a limited number of large industrial processes, to measure emissions directly, so the NAEI is based on highly detailed assumptions on the amount of each air pollutant generated from different fuel use and activities in the UK.