Preprints
https://doi.org/10.5194/egusphere-2025-3824
https://doi.org/10.5194/egusphere-2025-3824
28 Aug 2025
 | 28 Aug 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Surface Ozone Distribution & Trends Over Ireland : Insights from long-term measurement record and source attribution modelling

Nikhil Korhale, Tabish Ansari, Tim Butler, Jurgita Ovadndevaite, Colin D. O'Dowd, and Liz Coleman

Abstract. Surface ozone (O3) pollution is assessed across Ireland with a focus on long-term trends with a specific focus on the Mace Head atmospheric research station which monitors background O3 advected into Europe via prevailing South Westerlies. Using innovative trajectory analysis, O3 concentrations, exceedances and were identified by sectors, revealing distinct seasonal and spatial patterns. Findings show a significant rising trend in surface O3 at Irish urban sites over the past two decades but without a similar trend at coastal sites. Highest O3 levels and exceedances were observed at remote coastal sites, less influenced by local emissions, and heavily influenced by meteorological processes, including transboundary pollution and stratospheric intrusion. At Mace Head, springtime O3 levels show a declining trend, with a rising winter-time trend. Looking only at the clean sector, the springtime decline remains significant; but without rising wintertime trends, implying the rising winter trends are a response to declining European emissions. Advanced modelling tools are used to quantify O3 source contributions, elucidating key drivers behind the observed changes. Characteristic springtime O3 maxima at Mace Head are attributed to stratospheric transport, influences from westerly transboundary air pollution, and lightning NOx. Combined trend and sectoral observational analysis reveals that total spring-time concentrations are in decline, with exceedances from the UK & continental sector declining at a greater rate. This research highlights the importance of seasonal factors in air quality management across Ireland, emphasising the need for a multi-faceted approach to control O3 levels and reduce exceedances through global and regional emission reductions.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Nikhil Korhale, Tabish Ansari, Tim Butler, Jurgita Ovadndevaite, Colin D. O'Dowd, and Liz Coleman

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Nikhil Korhale, Tabish Ansari, Tim Butler, Jurgita Ovadndevaite, Colin D. O'Dowd, and Liz Coleman
Nikhil Korhale, Tabish Ansari, Tim Butler, Jurgita Ovadndevaite, Colin D. O'Dowd, and Liz Coleman

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Short summary
We investigate the distribution and trends of surface ozone and its precursors over Ireland using advanced modelling to determine the drivers of ozone. Trajectory analysis is used to trace the origins of air masses, revealing the impact of transboundary pollution and atmospheric transport. The rising trend has been observed at urban sites over the past two decades, but without a similar trend at coastal sites. Coastal areas consistently show higher ozone levels than rural and urban areas.
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