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

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.