Road transport sector produces a significant quantity of ground level ozone (O 3 ) precursors. Relevant abatement of exhaust emissions has been achieved in Europe during last decades due to environmental policy. Presented results indicate relatively weak response of key O 3 precursors decrease: NO x (-40%), NMVOC (-69%), and CO (-63%) from the EU-25 road transport to O 3 concentration at background site Stará Lesná in Slovakia for time period 1992-2005. At this site mean annual O 3

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... varies around 63.4 μg m -3 and detected slight decrease of -0.89 μg m -3 /decade is not statistically significant. Furthermore, high O 3 concentrations occurred in the High Tatra Mts region during the August 2003 heat wave which showed an important impact of long-range air pollution on air quality of Slovak mountain region. More studies will be needed to specify the role of meteorological and environmental factors in the transport and transformation of emissions from large urban regions to remote sites.