Atmos. Chem. Phys. Discuss., 12, 2025-2056, 2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Can a global model reproduce observed trends in summertime surface ozone levels?
S. Koumoutsaris1,* and I. Bey2
1International Space Science Institute, Bern, Switzerland
2Center for Climate Systems Modeling, ETH Zurich, Zurich, Switzerland
*now at: Risk Management Solutions, EC3R 8NB, London, UK

Abstract. Quantifying trends in surface ozone concentrations are critical for assessing pollution control strategies. Here we use observations and results from a global chemical transport model to examine the trends (1991–2005) in daily maximum 8-hour average concentrations in summertime surface ozone at rural sites in Europe and the United States. We find a decrease in observed ozone concentrations at the high end of the probability distribution at many of the sites in both regions. The model attributes these trends to a decrease in local anthropogenic ozone precursors, although simulated decreasing trends are overestimated in comparison with observed ones. The low end of observed distribution show small upward trends over Europe and the western US and downward trends in Eastern US. The model cannot reproduce these observed trends, especially over Europe and the western US. In particular, simulated changes between the low and high end of the distributions in these two regions are not significant. Sensitivity simulations indicate that emissions from far away source regions do not affect significantly ozone trends at both ends of the distribution. This is in contrast with previously available results, which indicated that increasing ozone trends at the low percentiles may reflect an increase in ozone background associated with increasing remote sources of ozone precursors. Possible reasons for discrepancies between observed and simulated trends are discussed.

Citation: Koumoutsaris, S. and Bey, I.: Can a global model reproduce observed trends in summertime surface ozone levels?, Atmos. Chem. Phys. Discuss., 12, 2025-2056, doi:10.5194/acpd-12-2025-2012, 2012.
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