Decrease in surface ozone concentrations at Mediterranean remote sites and increase in the cities

Analyzing hourly ozone data from 214 European background sites over the time period 2000-2010, we demonstrated for the first time that the ozone control measures are effective at rural sites, while ozone concentrations are still increasing in the cities. The Western European Mediterranean basin is expected to be more strongly affected by climate change, including ozone pollution, than most of the other regions of the world. At 58% of the rural sites significant decreases were found resulting in an average - 0.43% per year while an increase was recorded in urban and suburban stations (+0.64% year−1 and +0.46% year−1, respectively). At cities ozone average levels increased, but the peak ozone concentrations decreased. In all station types, a significant reduction in the amplitude of peak ozone concentrations was found at more than 75% of stations (98th percentile, −0.77% year−1; hourly peak, −1.14% year−1 and daily average peak, −0.76% year−1). The peak reduction may largely be attributed to the reduction in NOx and VOC emissions within the European Union which started in the early 1990s. The results suggested a convergence of ozone pollution at remote and urban sites all around the Western European Mediterranean basin.