What is photochemical air pollution?Photochemical air pollution is the pollution of the ambient air with chemical substances such as ozone (O3), peroxyacetyl nitrate, nitrogen dioxide (NO2), hydrogen peroxide and other substances with an oxidizing function. These substances are created on hot days under the influence of sunlight when nitrogen oxides (NOx) and non-methane volatile organic compounds (NMVOC) are present. NOx and NMVOC are also called the ‘precursors’ of photochemical air pollution (or ozone precursors).
Traffic is primarily responsible for the emissions of these ozone precursors, but also industry, the energy sector and households contribute to the emissions.
Ozone and the impact of ozone
Ozone is the representative substance for the photochemical air pollution in the troposphere. It has a highly oxidizing character and is harmful to man, plants and materials. Ozone may result in respiratory problems, cause reduced yield and stress-resistance of crops and degrades some materials and artworks.
A cross-border problemPhotochemical air pollution is a problem that crosses borders. Only a European coordinated, large-scale and sustainable decrease of the emissions of ozone precursors (NOx and NMVOC) can keep this problem within bounds. An EU-strategy for combating photochemical air pollution and acidification has been formulated. This resulted in an EU directive (2001/81/EC) with National Emission Ceilings (NEC) for each member state, linked to a new EU-directive for ozone in ambient air (2002/3/EC).