Unlike stratospheric ozone, which protects us from UV light, atmospheric low-level ozone is a pollutant affecting the respiratory system. It is produced under the effect of solar radiation from industrial pollutants that are by-products of incomplete combustion.

For the past few decades, European regulations to limit emissions of ozone precursors have resulted in improved air quality, and could potentially continue to bear fruit by 2050. This study however shows that climate change and the accompanying polluting emissions from outside Europe are changing the game.

In the case of a 2 °C temperature rise by 2050, this policy will no longer allow to improve air quality in Europe. With +3 °C, the air quality would deteriorate sharply, especially in south-eastern Europe, where the health of populations could be seriously exposed—100 days per year on average, instead of 25.

These results were obtained as part of a European project, from computer simulations using a cascade of atmospheric chemistry and climate models. According to the sensitivity tests carried out, the decrease in air quality is mainly driven by the increase in ozone concentrations on a global scale. Under the +3 °C scenario, climate experts report doubled global methane concentrations, a gas which, on top of its strong greenhouse effect, is an ozone precursor.

According to this study, preserving air quality will need more than sustaining the efforts to reduce polluting gas emissions in Europe—it will also require bolstering climate policies. For example, a reduction in global methane emissions would have beneficial effects, both for global warming mitigation and air quality improvement.