Areas under high ozone and nitrogen loads are spatially disjunct in Czech forests.

It is widely accepted that excessive loads of nitrogen (N) deposition and ambient ozone (O3) endanger natural ecosystems and the environment. Despite substantial reductions in emissions since the early 1990s both in the Czech Republic and in neighbouring countries, neither O3 exposures nor N deposition have yet decreased to acceptable levels relative to the recommended thresholds. Based on long-term monitoring and high-quality data, we have indicated the areas of special risk due to high N deposition and O3 exposures in Czech forests in 2000-2015. The areas of potential risk denote those forests under the highest loads of N deposition and O3 exposure on a regular basis. The underlying classification approach is relativistic, i.e. based ultimately on quartiles of pollution intensities and not derived from critical limits or loads. The forest areas under the highest O3 exposures and N deposition are spatially disjunct. The highest O3 exposures are in the southern and the highest N deposition is in the northern Czech Republic. In contrast to our assumption, only 1322 km2, i.e. 4.6% of the total forested area (28,782 km2) are overlapping areas with a potential risk due both to high O3 exposures and to N deposition. Our results provide valuable input information for a more detailed environmental analysis, anticipated in the future, addressing to what extent the indicated areas at potential risk are associated with the actual negative impacts on forests.