Distribution and Long-Term Trends of Tropospheric Ozone Concentrations in Ireland

Abstract

Tropospheric ozone (O3) is highly variable over space and time reflecting local production and destruction as well as addition and loss through regional and long-range transport. In this study, O3 concentrations at 11 stations in Ireland and their long-term trends (7–9 sites) were evaluated; O3 concentrations (2015–2019) varied spatially, with the highest annual mean concentrations along the Atlantic west coast (69–75 µg/m3), and the lowest in urban centres (39–43 µg/m3). Ozone followed a seasonal pattern of spring and winter maximum and summer–autumn minimum. Significant long-term (2005–2019) increases were observed in annual O3 concentration at two rural stations, while increases were larger and more frequent during winter with increases at four out of seven stations. During the decade 2010–2019, significant annual increases were observed at four out of nine stations. Observed site- and season-specific increasing trends in O3 concentrations likely reflected changes in regional precursor gas emissions sources. Despite reported decreases in background concentrations in the marine boundary layer in northern mid-latitudes in recent decades, O3 concentrations at some sites in Ireland have increased significantly primarily driven by changes in winter concentrations. There were no significant decreasing trends at any site or in any season.