Future levels pan-European surface ozone concentrations

SUDPLAN Newsletter 2 (February 2012): For air quality future projections, uncertainties are not only found in future climate but also in how European emissions will evolve and how hemispheric air pollution levels will change.

Climate change affects air quality due to the inherent link between ambient weather and the source/sink processes controlling the local concentration of air pollutants. Here we report from studies that have investigated future concentrations of surface ozone (O3) in Europe. We compare the effect of climate change to the impact of projected European emission changes and increased background concentrations of ozone and methane.

We find that although climate change and increasing background concentrations both act to increase surface ozone, the expected reduction in European ozone precursor emissions dominates. For most parts of Europe we foresee lower surface ozone in the future. Exceptions are the British Isles and Scandinavia where the increasing hemispheric concentrations of ozone may lead to future increases in surface ozone.

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Figure 1. Trend in annual-mean summer-time (April-September) surface O3 concentration averaged over land areas in six European regions (see Figure 2). Enlarge Image

To study future O3 over Europe we make use of a model chain starting with global climate models (GCMs) which feeds boundary conditions into a regional climate model (RCM) with higher spatial resolution over Europe. The resulting meteorological output from the RCM is next used to drive the simulation of emissions, transport, atmospheric chemistry and deposition of air pollutants in a chemistry transport model (CTM) over Europe.

We use the regional off-line CTM MATCH to simulate the evolution of O3 and other air pollutants over Europe. Anthropogenic emissions of air pollutants are taken from the RCP4.5 inventory which comprises consistent global emissions of air pollutants from 1960 to 2100. For background concentrations we assume, in our base case, increasing hemispheric concentrations of +0.2 ppb(v) yr-1 –consistent with observations over the last few decades.

Figure 1 shows the temporal evolution of modeled surface O3 during summer in the regions depicted in Fig. 2. The different experiments are summarized in Table 1. Climate change alone causes increasing O3 in southern and central Europe but decreasing O3 in Northern Europe. The difference in driving meteorology between the downscaling of HadCM3 and ECHAM5 results in different O3 levels, while the trend remain similar in all regions. The projected change in O3 precursor emissions leads to decreasing O3 concentrations across Europe despite the “climate penalty” imposed in southern Europe. Including a trend in hemispheric background concentrations leads to stable or increasing O3 concentrations in Scandinavia and the British Isles while concentrations will still go down in central and southern Europe.

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Figure 2. Regions of Europe.

References

Engardt, M., Langner, J. and Andersson, C., 2012: Future levels pan-European surface ozone concentrations. Submitted to Atmospheric Chemistry and Physics.