Air pollution by ozone and health (CLIM 006) - Assessment published Nov 2012

Key policy question: What are health effects of ozone exposure across Europe, and how are they changing?

Annual mean ozone concentrations by station type

Note: Annual mean ozone concentrations by station type

Data source:

• AirBase - The European air quality database provided by  European Environment Agency (EEA)

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Modelled change in tropospheric ozone concentrations over Europe

Note: The modelled changes shown are only due to climate variability and climate change

Data source:

• Interannual variationand trends in air pollution over Europe due to Climate variability during 1958-2001 simulated with a regional CTM coupled to the ERA40 reanalysis provided by Swedish meteorological and hydrologiska insitute (SMHI)

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Key assessment

Past trends

There is no clear trend in the annual mean concentration of ozone recorded at different types of stations (urban vs. rural) over the period 1999–2009, although there is a slight decreasing tendency since 2006 in rural stations, at various geographical levels, both low-level and high-level (Figure 1). Meanwhile, a slight tendency towards increased annual mean concentrations is detected close to traffic. Ozone precursor emissions in Europe have been cut substantially recently whereas average ozone concentrations in Europe have largely stagnated. Meteorological variability and climate change could play a role in this discrepancy, including by increasing emissions of biogenic non-methane volatile organic compounds (NMVOCs) during wildfires, but increasing intercontinental transport of ozone and its precursors in the Northern Hemisphere also needs to be considered [i]. Formation of tropospheric ozone from increased concentrations of CH₄ may also contribute to the sustained ozone levels in Europe [ii].

The relative contributions of local or regional emission reduction measures, specific meteorological conditions (such as heat waves), hemispheric transport of air pollution and emissions from natural sources (such as wildfires), on overall ozone concentrations is difficult to estimate. A statistical analysis of ozone and temperature measurements in Europe for 1993–2004 shows that in central-western Europe and the Mediterranean area a change in the increase in daily maximum temperatures in 2000–2004 compared with 1993–1996 contributed to extra ozone exceedances. In southern and central Europe, the observed temperature trend was responsible for 8 extra annual exceedance days (above the threshold of 120 μg/m³) on average, which corresponds to 17 % of the total number of exceedances observed in that region [iii]. A modelling study suggests that observed climate variability and change have contributed to increased ozone concentrations during the period 1979–2001 in large parts of central and southern Europe (Andersson et al., 2007). The reason for this is a combination of changes in temperature, wind patterns, cloud cover and atmospheric stability. Temperature plays a role in various processes which directly affect the formation of ozone, like the emission of biogenic NMVOCs, for example isoprene, and the photo-dissociation of nitrogen dioxide (NO₂).

A study by [iv] showed that ozone trends in Europe in the years 1997–1998 were influenced by El Niño and biomass burning events and in the year 2003 by the heat wave in north-west Europe. The study did not conclude on the impact of emission reduction on long-term ozone trends, due to the influence of meteorological variability, changes in background ozone and shift in emission source patterns. Decreased anthropogenic emissions of some ozone precursors (NO_X, CO, and some NMVOCs) in the past two decades have reduced the number of peak ozone concentrations [v].

In order to understand historical tropospheric ozone trends, further retrospective sensitivity analysis of precursor emission changes and hindcast modelling of ozone concentrations are needed to quantify the impact and variability of the various factors influencing ozone levels. Figure 2 shows the estimated trends in tropospheric ozone concentrations over Europe for two time periods derived from such hindcast modelling. There has been a marked increase in ozone concentrations in many regions from 1978 to 2001. However, taking into account a longer perspective starting from 1958, increases are limited to a few European regions. Unfortunately, more recent data is not available.

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 1 below) [vi]. Nevertheless, quantification of future levels of ground-level ozone remains uncertain due to the complex interaction of these processes. Available studies indicate that projected climate change affects different regions in Europe differently, by increasing average summer ozone concentrations in southern Europe and decreasing them over northern Europe and the Alps [vii]. Preliminary results indicate that in a long time perspective (2050 and beyond), envisaged emission reduction measures of ozone precursors have a much larger effect on concentrations of ground-level ozone than climate change [viii]. Climate change in combination with the emission reductions will influence the future levels of ground-level ozone.

Table 1 Selection of meteorological parameters that might increase under future climate change and their impact on ozone levels

Source: [ix]

[i] EEA, Air Pollution by Ozone Across Europe During Summer 2009 EEA Technical report (Copenhagen: European Environment Agency, 2010), http://www.eea.europa.eu/publications/air-pollution-by-ozone-across-europe-during-summer-2009; EEA, The European Environment – State and Outlook 2010: Air Pollution — SOER 2010 Thematic Assessment (Copenhagen: European Environment Agency, 2010), http://www.eea.europa.eu/soer/europe/air-pollution.

[ii] EEA, Air Pollution by Ozone Across Europe During Summer 2011 EEA Technical report (Copenhagen: European Environment Agency, 2012), http://www.eea.europa.eu/publications/air-pollution-by-ozone-2011.

[iii] EEA, Impacts of Europe’s Changing Climate - 2008 Indicator-based Assessment. Joint EEA-JRC-WHO Report EEA Report (Copenhagen: European Environment Agency, 2008), http://www.eea.europa.eu/publications/eea_report_2008_4.

[iv] R. C. Wilson et al., “Have Primary Emission Reduction Measures Reduced Ozone Across Europe? An Analysis of European Rural Background Ozone Trends 1996–2005,” Atmospheric Chemistry and Physics 12, no. 1 (January 9, 2012): 437–454, doi:10.5194/acp-12-437-2012.

[v] EEA, Air Quality in Europe — 2011 Report EEA Technical report (Copenhagen: European Environment Agency, 2011), http://www.eea.europa.eu/publications/air-quality-in-europe-2011; EEA, Air Pollution by Ozone Across Europe During Summer 2011.

[vi] Daniel J. Jacob and Darrell A. Winner, “Effect of Climate Change on Air Quality,” Atmospheric Environment 43, no. 1 (January 2009): 51–63, doi:10.1016/j.atmosenv.2008.09.051; P.S. Monks et al., “Atmospheric Composition Change – Global and Regional Air Quality,” Atmospheric Environment 43, no. 33 (October 2009): 5268–5350, doi:10.1016/j.atmosenv.2009.08.021.

[vii] C. Andersson and M. Engardt, “European Ozone in a Future Climate: Importance of Changes in Dry Deposition and Isoprene Emissions,” Journal of Geophysical Research 115, no. D2 (January 22, 2010), doi:10.1029/2008JD011690; J. Langner, M. Engardt, and C. Andersson, “European Summer Surface Ozone 1990-2100,” Atmospheric Chemistry and Physics Discussions 12, no. 3 (March 16, 2012): 7705–7726, doi:10.5194/acpd-12-7705-2012.

[viii] J. Langner, M. Engardt, and C. Andersson, “Modelling the Impact of Climate Change on Air Pollution over Europe Using the MATCH CTM Linked to an Ensemble of Regional Climate Scenarios,” in Air Pollution Modelling and Its Application XXI, ed. Douw G. Steyn and Silvia Trini Castelli, vol. 4 (Dordrecht: Springer Netherlands, 2011), 627–635, http://www.springerlink.com/index/10.1007/978-94-007-1359-8_103.

[ix] Royal Society, Ground-level ozone in the 21st century: future trends, impacts and policy implications. Fowler, D. (Chair) Science Policy Report (London: The Royal Society, 2008), http://royalsociety.org/policy/publications/2008/ground-level-ozone/.