Differents scales

The phenomena concerning air pollution can be considered on three scales of space and time :

• local level or proximity pollution, with a timescale of hours,
• regional level or long distance pollution with a timescale of days,
• global level or planetary pollution, with a timescale of years.

Each of these scales has its different problems.

Proximity pollution
Since the 19th century, people have been interested in air pollution in cities and densely-populated areas because that is where most sources of pollution from human activities are found and where the great majority of the population live, breathing in the polluted air.
Most of the classic atmospheric pollutants (SO₂, NOx, CO, O₃, lead and particles) have effects on human health, ecosystems and buildings.

Long distance pollution
A proportion of the pollutants emitted by human activities falls close to its source, but some falls hundreds or even thousands of kilometres away. The main problems with long distance pollution are acidification, eutrophication and photochemical pollution.

Planetary pollution
This type of pollution was revealed in the 1980s, with observations from researchers on the greenhouse effect and the depletion of the ozone layer.