Jump to content

Long-range transport of air pollutants

In the early 1970s, it was not known that pollutants could be transported over great distances with air currents and deposited elsewhere with precipitation.

Air pollution was seen as a domestic rather than an international issue. The notion that industrial emissions in one country could contaminate another country was contentious. Researchers who made such claims had to prove them.

Research breakthrough

The breakthrough was the research report “Long-Range Transport of Air Pollutants. Measurements and Findings” which NILU compiled for the Organisation for Economic Co-operation and Development (OECD) in 1977. This research report was crucial for the understanding of how far air pollution could spread.

The report clearly showed that pollution could be transported over large distances and that individual countries could do very little to reduce acid rainfall solely through national measures.

The Convention on Long-Range Transboundary Air Pollution

In 1979, the Convention on Long-Range Transboundary Air Pollution (LRTAP) was established. Its aim was to create an understanding that air pollution can spread across borders – that is, pollution in one country can lead to negative effects in another.

The convention includes eight protocols that identify specific measures that the member states are obliged to implement to cut their own emissions.

The initial LRTAP work was led by NILU, and the institute has since played active roles in international climate cooperation.

What is long-range transboundary air pollution?

Long-range transboundary air pollution includes acidifying gases such as sulphur oxides (SOx) and nitrogen oxides (NOx), ground-level ozone, particulate matter (dust) and environmental pollutants such as heavy metals and persistent organic pollutants (POPs).

Acid rain and eutrophication

Questions related to the acidification and eutrophication of rivers, water and soil have been a central research area for NILU for several decades.

In the 1960s, scientists discovered the relationship between sulphur oxide emissions from Europe and the acidification of waterways in Scandinavia. Mortality among fish populations in southern Norway was eventually linked to long-range transboundary air pollution in the form of sulphur oxides and nitrogen oxides from the continent.

It was also found that ammonia emissions from agriculture and other sources could lead to eutrophication of waterways, which in turn promoted algal growth and oxygen depletion.

Facts about ground-level ozone

Ground-level ozone is a major environmental problem. Ozone gas can damage health and vegetation, reduce agricultural productivity and slow the decomposition of organic matter. In addition, ozone is an important greenhouse gas.

The gas ozone (O3) occurs throughout the atmosphere. The term “ground-level ozone” is used both for ozone near the ground and ozone anywhere in the troposphere, from the Earth’s surface up to about 10 km altitude.

Ground-level ozone forms through chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs).

The ozone in the stratosphere (10-15 km above the surface of the Earth) is called the ozone layer.

Facts about particles

Atmospheric particles are important for both climate and local air quality. At present, scientists know too little about how particles affect the atmosphere, and this is a major source of uncertainty in our understanding of climate change.

Particles can contribute to both cooling and heating, depending on their chemical composition and optical properties. Particles are defined as short-lived climate drivers.

Aerosols in the atmosphere consist of solid particles, liquid droplets, or a mixture of both, suspended in air or gas. The chemical composition of aerosols varies greatly, and the particles vary greatly in size. This variability is due to the fact that aerosols come from countless sources and are formed by a multitude of mechanisms.

Particles can be released directly into the atmosphere (primary particles) or formed from precursor gases (secondary particles) such as SO2 and VOCs. Particles are also formed when cloud droplets evaporate.

The higher the number of particles in a cloud, the more particles are available on which to distribute condensing water vapor. This makes the cloud whiter and more long-lived than usual. In addition, the process cools the Earth’s surface, as whiter clouds reflect more sunlight before it reaches the ground.