Abstract
Abstract. The impacts of changes in ozone precursor emissions as well as climate change on the future ozone exposure of the vegetation in Europe were investigated. The ozone exposure is expressed as AOT40 (Accumulated exposure Over a Threshold of 40 ppb O3) as well as PODY (Phytotoxic Ozone Dose above a threshold Y). A new method is suggested to express how the length of the period during the year when coniferous and evergreen trees are sensitive to ozone might be affected by climate change. Ozone precursor emission changes from the RCP4.5 scenario were combined with climate simulations based on the IPCC SRES A1B scenario and used as input to the Eulerian Chemistry Transport Model MATCH from which projections of ozone concentrations were derived. The ozone exposure of vegetation over Europe expressed as AOT40 was projected to be substantially reduced between the periods 1990–2009 and 2040–2059 to levels which are well below critical levels used for vegetation in the EU directive 2008/50/EC as well as for crops and forests used in the LRTAP convention, despite that the future climate resulted in prolonged yearly ozone sensitive periods. The reduction in AOT40 was mainly driven by the emission reductions, not changes in the climate. For the toxicologically more relevant POD1 index the projected reductions were smaller, but still significant. The values for POD1 for the time period 2040–2059 were not projected to decrease to levels which are below critical levels for forest trees, represented by Norway spruce. This study shows that substantial reductions of ozone precursor emissions have the potential to strongly reduce the future risk for ozone effects on the European vegetation, even if concurrent climate change promotes ozone formation.
Highlights
Surface ozone (O3) is the most important gaseous air pollutant with respect to effects on vegetation on regional and global scales (Hollaway et al, 2012; Mills et al, 2011; Royal Society, 2008)
This study considered the combined effect of projected emission reductions according to the RCP4.5 air pollutant emission scenario and climate change under the IPCC SRES A1B scenario during the period 1960–2100
Over wide areas AOT40 will, by the time period 2040– 2059, decrease to levels which are well below O3 critical levels used for vegetation in the EU legislation as well as critical levels used in the LRTAP convention
Summary
Surface ozone (O3) is the most important gaseous air pollutant with respect to effects on vegetation on regional and global scales (Hollaway et al, 2012; Mills et al, 2011; Royal Society, 2008). The concentration of surface O3 is affected by a number of factors including (1) concentrations of O3 precursors, which are a function of anthropogenic emissions and the mixing and transport in the atmosphere, (2) effects of temperature and solar radiation on the rate of chemical reactions and on emissions of biogenic VOCs, which may enhance O3 formation (Doherty et al, 2013) and (3) deposition to vegetated and non-vegetated surfaces, which depends on both vertical air mixing (Klingberg et al, 2012) and the Published by Copernicus Publications on behalf of the European Geosciences Union. J. Klingberg et al.: Declining ozone exposure of European vegetation effects of air and soil humidity, solar radiation and temperature on vegetation gas exchange (Tuovinen et al, 2009)
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