Characteristics of ozone pollution
Ozone concentrations become particularly high in summertime in regions with high emissions from traffic and industry.
During the day, ozone concentrations will usually build up and peak in the afternoon. At night-time ozone concentrations decline.
Ozone concentrations peak in summer-time:
...And in the afternoon, because the formation of ozone needs sunlight:
In summer 2003, the heatwave in southern, western and central Europe gave rise to a record number of instances of severe ozone pollution. However, ozone episodes were less frequent in 2004, 2005 and 2006.
The highest concentrations of ozone are not always found in city centres where the pollutants that form ozone are emitted. The reason is that where there is an abundance of nitrogen oxide from traffic, ozone formation is suppressed. As a result, its concentration is sometimes low in busy urban centres.
Ozone may also be transported by the wind over distances of 400-500 km a day. Hence, ozone pollution may eventually be found in suburban and rural areas far away from the sources of the pollutants. So, ozone levels in surburban areas can actually be higher than in urban centres.
When ozone mixes with other air pollutants like particulate matter (PM) and nitrogen oxides (NOx), it can form a harmful smog. This smog occasionally occurs in polluted city areas. More information on air quality is on the EEA's website in the air quality section.