Trend reversal from high-to-low and from rural-to-urban ozone concentrations over Europe

The trends per 5th percentile interval of European surface ozone concentrations over urban, suburban and rural sites in the period 1995 –2012 have been estimated based on observational data from the European Environment Agency air quality database. Consistent with previous study results, we find a rapid decline of relatively high ozone concentrations after the year 1995, especially of rural summertime ozone. However, the decreasing rate has slowed, and even reversed, of low-level ozone, especially in the urban environment for all seasons. Although the ozone air pollution problem has been declared to be eff ectively resolved by achieving European air quality goals, our results indicate that ozone remains to be di fficult to control for a long time into the future. Global and regional models poorly reproduce the measured di fferences in ozone and trends in di fferent levels and regions. Thus policy guidelines from the model should be considered with care.