| Summary: | A case study of two episodes with elevated ozone concentrations in Germany provides strong evidence, that a great portion of the pollution level is caused by the extensive accumulation of ozone in the particular air mass and by supra-regional transport of ozone and its precursors. This depends on meteorological conditions for photochemical ozone production during transport and whether regions of high NOx- and VOC-emission rates are met by the air mass trajectories. They were calculated backward for various reception points and compared with the distribution of the ozone concentrations using all available measured values in Germany. Especially in the northern and northeastern part of the country, located at the edge of the high industrialized Central European region, high levels of ozone seem to be accompanied by trajectories from the sector southwest to southeast, when advection of air masses with subtropical and continental characteristic takes place.
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