Past, present and future concentrations of ground-level ozone and potential impacts on ecosystems and human health in northern Europe

Abstract This review summarizes new information on the current status of ground-level ozone in Europe north of the Alps. There has been a re-distribution in the hourly ozone concentrations in northern Europe during 1990–2015. The highest concentrations during summer daytime hours have decreased while the summer night-time and winter day- and night-time concentrations have increased. The yearly maximum 8-h mean concentrations ([O 3 ] 8h,max ), a metric used to assess ozone impacts on human health, have decreased significantly during 1990–2015 at four out of eight studied sites in Fennoscandia and northern UK. Also the annual number of days when the yearly [O 3 ] 8h,max exceeded the EU Environmental Quality Standard (EQS) target value of 60 ppb has decreased. In contrast, the number of days per year when the yearly [O 3 ] 8h,max exceeded 35 ppb has increased significantly at two sites, while it decreased at one far northern site. [O 3 ] 8h,max is predicted not to exceed 60 ppb in northern UK and Fennoscandia after 2020. However, the WHO EQS target value of 50 ppb will still be exceeded. The AOT40 May–July and AOT40 April–September metrics, used for the protection of vegetation, have decreased significantly at three and four sites, respectively. The EQS for the protection of forests, AOT40 April–September 5000 ppb h, is projected to no longer be exceeded for most of northern Europe sometime before the time period 2040–2059. However, if the EQS is based on Phytotoxic Ozone Dose (POD), POD 1 , it may still be exceeded by 2050. The increasing trend for low and medium range ozone concentrations in combination with a decrease in high concentrations indicate that a new control strategy, with a larger geographical scale than Europe and including methane, is needed for ozone abatement in northern Europe.