In North America and Europe, emissions of ozone precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) declined by half between 2000 and 2018. However, the ozone content of the air—and thus the risk to human health—has not decreased proportionally. Until now, theories abo ut the causes have been largely based on conjecture. Scientists from the Research Institute for Sustainability (RIFS) at GFZ and collaborators have now provided more clarity. Their study, published in Atmospheric Chemistry and Physics, shows that the weaker-than-expected decline of ozone is mainly driven by increased transport of ozone produced abroad. ...read more read less