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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Sep 2018

Research article | 17 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Ozone source apportionment during peak summer events over southwestern Europe

Maria Teresa Pay1, Gotzon Gangoiti2, Marc Guevara1, Sergey Napelenok3, Xavier Querol4, Oriol Jorba1, and Carlos Pérez García-Pando1 Maria Teresa Pay et al.
  • 1Earth Sciences Department, Barcelona Supercomputing Center, BSC, c/Jordi Girona, 29, 08034 Barcelona, Spain
  • 2Department of Chemical and Environmental Engineering, University of the Basque Country UPV/EHU, ETSI-Bilbao School of Engineering, Alda. de Urquijo s/n, E-48013 Bilbao, Spain
  • 3U.S. EPA, Research Triangle Park, NC, USA
  • 4Institute of Environmental Assessment and Water Research, IDAEA-CSIC, c/Jordi Girona, 18-26, 08034 Barcelona, Spain

Abstract. It is well established that in Europe, high O3 concentrations are most pronounced in southern/Mediterranean countries due to the more favorable climatological conditions for its formation. However, the contribution of the different sources of precursors to O3 formation within each country relative to the imported (regional and hemispheric) O3 is poorly quantified. This lack of quantitative knowledge prevents local authorities from effectively designing plans that reduce the exceedances of the O3 Target Value set by the European Air Quality Directive. O3 source attribution is a challenge because the concentration at each location and time results not only from local biogenic and anthropogenic precursors, but also from the transport of O3 and precursors from neighbouring regions, O3 regional and hemispheric transport and stratospheric O3 injections. Our study applies and thoroughly evaluates a countrywide O3 source apportionment method implemented in a Chemical Transport Model (CTM) at high resolution (4 × 4km) over the Iberian Peninsula (IP) to understand and quantify the origin of peak O3 events over a 10-day period covering the most frequent synoptic summer conditions in the IP. The method tags both O3 and its gas precursor emissions from source sectors within one simulation and each tagged species is subject to the typical physical processes (advection, vertical mixing, deposition, emission and chemistry) as the actual conditions remain unperturbed. We quantify the individual contributions of the largest NOx local sources to high O3 concentrations compared to the contribution of imported O3. We show for the first time that imported O3 is the largest input to the ground-level O3 concentration in the IP, accounting for 46% to 68% of the daily mean O3 concentration during exceedances of the European Target Value. The hourly imported O3 increases during typical northwestern advections (70–90%, 60–80µg/m3), and decreases during typical stagnant conditions (30–40%, 30–60µg/m3) due to the local NO titration effect. During stagnant conditions, the anthropogenic precursors control the O3 peaks in areas downwind of the main urban and industrial regions (up to 40% in hourly peaks). We also show that ground-level O3 concentrations are strongly affected by vertical mixing of O3-rich layers present in the free troposphere, which result from local/regional layering and accumulation, and continental/hemispheric transport. Indeed, vertical mixing largely explains the presence of imported O3 at ground level in the Iberian Peninsula. Our results demonstrate the need for detailed quantification of the local and remote contributions to high O3 concentrations for local O3 management, being the O3 source apportionment an essential analysis prior to the design of O3 mitigation plans in any non-attainment area. To achieve the European O3 objectives in southern Europe, ad hoc local actions should be complemented by decided national and European-wide strategies.

Maria Teresa Pay et al.
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Status: final response (author comments only)
Status: final response (author comments only)
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Maria Teresa Pay et al.
Maria Teresa Pay et al.
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Publications Copernicus
Short summary
The poor diagnostic of the O3 problem over southwester EU prevents authorities from implementing effective mitigation plans. This work is a pioneer in identifying that the imported O3 is the largest input to the ground-level O3 concentration in the Iberian Peninsula, which is largely explained by the vertical mixing. The study also proves that the anthropogenic emissions control the severe O3 peaks during stagnant conditions. Ad hoc local actions should complement national/European strategies.
The poor diagnostic of the O3 problem over southwester EU prevents authorities from implementing...