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Indicator Assessment
Modelled future change (absolute and relative) in surface summertime ozone concentrations (left: daily average, right: daily maxima) over Europe at the middle of the century
Note: Absolute and relative difference between future (2041-2070) and present (1960-2010) summertime average daily and maxima ozone levels in a 9 model ensemble. The modelled changes shown are only due to climate variability and climate change. A diamond sign is plotted where the change is significant, and a plus sign is added where the change is robust across two-third of modelled years. The period 2041-2070 is taken as representative of the middle of the 21st century (2050)
Modelled future change (absolute and relative) in surface summertime ozone concentrations (left: daily average, right: daily maxima) over Europe at the end of the century
Note: Absolute and relative difference between future (2071-2100) and present (1960-2010) summertime average daily and maxima ozone levels in a 3 model ensemble. The modelled changes shown are only due to climate variability and climate change. A diamond sign is plotted where the change is significant, and a plus sign is added where the change is robust across two-third of modelled years. The period 2071-2100 is taken as representative of the end of the 21st century (2100)
Relative contribution of different factors to the net modelled ozone change
Note: The factors considered are intercontinental transport (‘bckd’, pink box), European emission strategies (‘emissions’, blue), and climate change (‘climate’, orange). The net (‘All’, white) modelled ozone change is expressed in SOMO35. Graph presents the modelled ozone change in 2050 compared to the present day for a reference (left) and climate mitigation (right) scenarios
Past trends
Between 2003 and 2012, there was no clear trend in the annual mean of the daily maximum eight hour average ozone concentrations, recorded at different types of station (traffic, urban, rural and other, mainly industrial), for the EU-28 as a whole (Figure 1).
Meteorological variability and climate change, as well as increasing emissions of biogenic non-methane volatile organic compounds (NMVOCs) during wildfires, could play a role in this lack of trends. Increasing intercontinental transport of ozone and its precursors in the northern Hemisphere also needs to be considered (EEA, 2010a, 2010b). The formation of tropospheric ozone from increased concentrations of methane (CH4) may also contribute to the sustained ozone levels in Europe (EEA, 2012).
The relative contributions of local or regional emissions reduction measures, specific meteorological conditions (such as heat waves), the hemispheric transport of air pollution and emissions from natural sources (such as wildfires), on overall ozone concentrations is difficult to estimate. Temperature plays a role in various processes that directly affect the formation of ozone, such as the emission of biogenic NMVOCs i.e. isoprene, and the photo-dissociation of nitrogen dioxide (NO2).
According to the EEA indicator 'Exceedance of air quality limit values in urban areas' (CSI 004), between 2000 and 2013, a significant proportion of the urban population in the EU-28 was exposed to ambient ozone concentrations above the European Union target value for the protection of human health. The maximum was registered in 2003 (58 %) and the minimum in 2012 (14 %)
The numbers of people exposed are higher in relation to the more stringent World Health Organization (WHO) guidelines, where they have been in the range of 93 – 99 %, with no discernible change over time.
Projections
Climate change is expected to affect future ozone concentrations due to changes in meteorological conditions, as well as due to increased emissions of specific ozone precursors (e.g. increased isoprene from vegetation under higher temperatures) and/or emissions from wildfires that can increase under periods of extensive drought. Most of the links between individual climate factors and ozone formation are well understood (see Table below, based in Jacob and Winner, 2009; Royal Society, 2008). Nevertheless, quantification of future levels of ground-level ozone remains uncertain due to the complex interaction of these processes.
|
Increase in ...
|
Results in ...
|
Impacts on ozone levels ...
|
|
Temperature |
Faster chemistry |
Increase |
|
|
Decomposition of nitrogen oxides' reservoir species (PAN) |
Increase |
|
Increased biogenic emissions (VOC, NO) |
Increase |
|
|
CO2 concentrations |
Decreased biogenic emissions |
Decrease |
|
Solar radiation (e.g. decreased cloudiness, or reduced aerosol optical depth) |
Faster photochemistry |
Increases (high NOx) |
|
Precipitation |
Scavenging of soluble precursors (HNO3) |
Decrease |
|
Atmospheric humidity |
Increased ozone destruction |
Increases (high NOx) |
|
Drought events |
Decreased atmospheric humidity and higher temperatures |
Increases |
|
Plant stress and reduced stomata opening |
Increases |
|
|
Increased frequency of wild fires |
Increases |
|
|
Blocked weather patterns |
More frequent episodes of stagnant air |
Increases |
|
Increase in summer/dry season heat waves |
Increases |
Available studies indicate that projected mid-century climate change (2041-2070) will increase surface ozone over the vast majority of continental Europe (Figure 2). It is only over the northern British Isles and Scandinavia that decreases can be found. Otherwise, over most of Central and Southern Europe, the increase is statistically significant and robust. For average ozone (maps on the left in figure 2), the increase is of the order of 2-3 µg.m-3 and only reaches 5 µg.m-3 over the Po Valley. Ozone peaks (maps on the right in figure 2) are found to be more sensitive, with increases of 5 µg.m-3 over Spain and Italy, as well as over populated areas of France, Germany, Belgium and scattered areas of Eastern Europe. Given the levels of background ozone, in relative terms, climate change is expected to contribute to an increase of about 2-5 %, reaching 7 % locally for ozone peaks.
Figure 3 shows climate change projections for the end of the century (2071-2100), where the magnitude of the impacts of climate change in terms of European surface ozone increases substantially. Summertime average ozone increases by 6 µg/m3 or more (or about 10 %) over most of continental Europe, and a similar increase for ozone peaks is found over polluted areas.
Preliminary results (Fig 4, adapted from Colette et al., 2013) also indicate that by the middle of the century, envisaged measures to reduce emissions of ozone precursors will have a much larger effect on concentrations of ground-level ozone than climate change. In the shorter term, the contribution of climate change is smaller, and it is not yet possible to assess the contribution of air quality legislation over the longer term.
Such results are obtained by performing air quality modelling sensitivity experiments with a combination of contributing factors frozen to their present or future conditions. Such contributing factors can be: (i) climate change, (ii) emission of air pollutants, (iii) long range transport, each of which are required to perform long term air quality simulations. Approximately one hundred years of simulation were required for such an assessment given the number of combinations required to explore various possible options, and the fact that in a climate context multi-annual simulations are needed. The computational cost of such assessment is such that, up to now, only a few similar attempts have been made. This makes uncertainty analysis difficult, hence the preliminary character of the results presented here.
Figure 4 shows that climate change (orange box), combined with emissions reductions (blue box) will influence future levels of ground-level ozone. Whereas for both reference and mitigation scenarios, climate change constitutes a penalty (orange box in the right part of the graph), its magnitude is much smaller than the benefit brought about by current air quality legislation (blue box in the left part of the graph). The role of intercontinental transport (pink box) is crucial and can drastically change the net result in Europe depending on the global climate and emissions pathways (penalty in the reference scenario and benefit in the mitigation one).
The indicator presents an overview of ozone concentrations over Europe in recent years, their effects on human health, and an estimate of the changes in these concentrations due to the effect of climate change. It presents the following:
The units used in this indicator are as follows:
High-levels of ozone cause breathing problems, trigger asthma, reduce lung function and cause lung disease (WHO, 2008). Epidemiological health evidence of chronic effects from exposure to ozone is now emerging, indicating considerably larger mortality effects than from acute exposure alone (WHO, 2013). The estimated effects of excessive exposure to ozone in 2010 for the EU-28 include about 26 500 premature deaths, 19 000 respiratory hospital admissions and 86 000 cardiovascular hospital admissions (people older than 64), and up to almost 109 million person-days with minor activity restrictions (all ages) (EU, 2013). The effect of ozone concentrations on total mortality, based on 2012 values, led to about 17 000 premature deaths in 40 European countries and about 16 000 in the EU-28 (EEA, 2015). There is scarce evidence that high ozone levels can further increase mortality during heat waves (ECDC, 2005; EPI, 2006).
In the Communication “A Clean Air Programme for Europe”, the EU Clean Air Policy Package, adopted by the European Commission on 18 December 2013, proposes the short-term objective of achieving full compliance with existing legislation (Air Quality Directive 2008/50/EC) by 2020 at the latest; and the long-term objective of no exceedences of the WHO guideline levels for human health.
Some of the priority objectives of the Seventh EU Environment Action Programme are to protect, conserve and enhance the EU's natural capital; safeguard its citizens from environment-related pressures and risks to health and well-being; and enhance the sustainability of its cities.
The European Commission and the European Environment Agency have developed the European Climate Adaptation Platform (Climate-ADAPT) to share knowledge on observed and projected climate change and its impacts on environmental and social systems and human health, relevant research, EU, national and sub-national adaptation strategies and plans, and adaptation case studies.
In April 2013, the European Commission presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change and a number of supporting documents. One of the objectives of the EU Adaptation Strategy is “Better informed decision-making”, which should occur through bridging the knowledge gap and further developing Climate-ADAPT as the ‘one-stop shop’ for adaptation information in Europe. Further objectives include “Promoting action by Member States” and “Climate-proofing EU action: promoting adaptation in key vulnerable sectors”. Many EU Member States have already taken action, such as by adopting national adaptation strategies, and several have also prepared action plans on climate change adaptation.
The following policy targets have been set:
Directive 2008/50/EC:
• A long-term objective for ozone levels of 120 microgram per cubic metre (µg/m3) as a maximum daily 8-hour mean within a calendar year (not to be exceeded any day). No attainment date specified.
• A target value for ozone, equal to the long-term objective, not to be exceeded more than 25 days per calendar year, averaged over three years. It had to be met in 2010 (average 2010 to 2012).
WHO Air Quality Guidelines:
• Daily maximum 8-hour mean of ozone concentrations: 100 µg/m3.
Clean Air Programme for Europe:
• Reduce ozone-acute-premature deaths in 2025 by between 28 and 39 % in relation 2005 figures.
Data on ozone concentrations is taken from AirBase (the European air quality database). From hourly data, the maximum daily 8-hour mean is calculated for every station that has levels of valid data upwards of 75 %. An annual average is calculated for every type of station (traffic, meaning urban, suburban and rural traffic stations; urban, meaning urban and suburban background stations; rural, meaning rural background stations; and others, meaning stations not falling in the previous categories, mostly industrial stations; see EU, 1997 for classification).
An ensemble of three-dimensional Chemistry Transport Models was used to study the impact of climate change on surface ozone. By comparing modelled ozone using future and present climate, while keeping anthropogenic emissions of ozone precursors constant, the absolute and relative climate ozone penalty can be computed. There have been a dozen of journal articles presenting such results for Europe over the past ten years. A combination of published projections has been used to calculate the multi-model ensemble mean climate impact on surface ozone. Among the 25 available model projections covering various scenarios and time horizons, the results for a median climate scenario (the A1B in the SRES set of scenarios (Nakicenovic et al., 2000)), which is covered by 9 and 3 models for the middle and the end of the century, respectively (Colette et al., 2015) is shown.
Finally, the respective contribution of the main factors influencing the future evolution of surface ozone can be quantified on the basis of air quality modelling sensitivity experiments, where the contributing factors are frozen to their present or future conditions. Such contributing factors are: (i) climate change, (ii) emissions of air pollutants, (iii) long range transport. Approximately one hundred years of simulation were required for such an assessment, given the number of combinations required to explore various possible options, and the fact that, for climate impact assessment, multi-annual simulations are needed (Colette et al., 2013).
Not applicable
As with other types of climate impact assessment, uncertainty is addressed by using multi-model ensembles. Statistical significance of the change was assessed with a p-value threshold of 0.05, and the change is considered robust when two-thirds of the models agree.
Ozone data is officially submitted by the national authorities. It is expected that data has been validated by the national data supplier and it should be in compliance with data quality objectives as described in the 2008 Air Quality Directive. There are different methods in use for the routine monitoring of pollutants.
Station characteristics and representativeness are, in some cases, insufficiently documented.
Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/)
No uncertainty has been specified
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/air-pollution-by-ozone-2/assessment or scan the QR code.
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