Ozone pollution is declining — but not everywhere
Ground-level air pollution Image © Marpix
Troublingly, efforts to combat European ozone levels are achieving only limited success. Although Europe has steadily reduced emissions of the air pollutants that lead to ozone formation in recent decades, ozone levels remain largely unchanged in many countries.
A new report by the European Environment Agency (EEA), released today, explores the reasons for this apparent contradiction, using data from the European air quality database, AirBase, and computer models to investigate ground-level ozone formation in Europe.
- The longest time series in AirBase (14–16 years) are available for four countries. These indicate that ground-level ozone has declined significantly in the Netherlands and the United Kingdom, falling during the 1990s and leveling off thereafter. No significant trends were identified in Austria and Switzerland.
- Inter-annual variations in weather conditions have a significant impact on yearly ozone levels. Discerning the effect of reduced ozone precursor emissions therefore requires long time series of data from stable monitoring networks. Unfortunately, extended time series are generally unavailable, particularly in southern Europe where ozone pollution is a major problem.
- Several unknowns complicate attempts to model ozone levels. Significant uncertainties exist regarding the magnitude and distribution of inter-continental inflows of ozone and its precursors, and the size and distribution of isoprene emissions from plants.
- The importance of meteorological conditions in ozone formation suggests that predicted changes in climate could also lead to increased ground-level ozone in many regions of Europe.
- Computer modelling was used to estimate the ozone levels that would arise if precursor emissions declined (as countries reported) or if they held constant at 1995 levels. The ozone levels recorded in 18 countries across Europe correspond more closely to the model output based on the assumption of declining emissions.
- Ground-level ozone has become a hemispheric or even global air pollution and climate change problem. Ozone abatement should be integrated into local, regional and global strategies and measures that simultaneously address emissions of air pollutants and greenhouse gases.