Drainage and conversion of natural peatlands to forestry increases soil CO₂ emissions through decomposition of peat and modifies the quantity and quality of litter inputs and therefore the soil carbon balance. In organic soils, CO₂ net emissions and removals are reported using carbon emission factors (EF). The choice of specific default Tier 1 EF values from the IPCC 2013 Wetlands supplement depends on land‐use categories and climate zones. However, Tier 1 EF for afforested peatlands in the temperate maritime climate zone are based on data from eight sites, mainly located in the hemiboreal zone, and the uncertainty associated with these default values is a concern. In addition, moving from Tier 1 to higher‐Tier carbon reporting values is highly desirable when large areas are affected by land‐use changes. In this study, we estimated site‐specific soil carbon balance for the development of Tier 2 soil CO₂‐C EFs for afforested peatlands. Soil heterotrophic respiration and aboveground tree litterfall were measured during two years at eight afforested peatland sites in Ireland. In addition, fine‐root turnover rate and site‐specific fine‐root biomass were used to quantify belowground litter inputs. We found that drainage of peatlands and planting them with either Sitka spruce or lodgepole pine, resulted in soils being net carbon sources. The soil carbon balance at multi‐year sites varied between 63 ± 92 and 309 ± 67 g C m⁻² year⁻¹. Mean CO₂‐C EF for afforested peatlands was 1.68 ± 0.33 t CO₂‐C ha⁻¹ year⁻¹. The improved CO₂‐C EFs presented here for afforested peatlands are proposed as a basis to update national CO₂‐C emissions from this land‐use class in Ireland. Furthermore, new data from these sites will significantly contribute to the development of more reliable IPCC default Tier 1 CO₂‐C EFs for afforested peatlands in the maritime temperate climate zone.

Understanding and quantifying soil respiration and its component fluxes are necessary to model global carbon cycling in a changing climate as small changes in soil CO₂ fluxes could have important implications for future climatic conditions. A soil respiration partitioning study was conducted in eight afforested peatland sites in south-west Ireland. Using trenched points, annual soil CO₂ emissions, and the contributions of root and heterotrophic respiration as components of total soil respiration, were estimated. Nonlinear regression models were evaluated to determine the best predictive soil respiration model for each component flux, using soil temperature and water table level as explanatory variables. Temporal variation in soil CO₂ efflux was driven by soil temperature at 10 cm depth, with all treatment points also affected by water table level fluctuations. The effect of water table level on soil respiration was best accounted for by incorporating a water level Gaussian function into the soil-temperature–soil-respiration model. Mean root respiration was 44% of mean total soil respiration, varying between 1100 and 2049 g CO₂ m⁻² year⁻¹. Heterotrophic respiration was divided between peat respiration and litter respiration, which accounted for 35 and 21% of total soil respiration, respectively. While peat respiration varied between 774 and 1492 g CO₂ m⁻² year⁻¹, litter respiration varied between 514 and 1013 g CO₂ m⁻² year⁻¹. Although the extrapolation of these results to other sites should be done with caution, the empirical models developed for the entire dataset in this study are a useful tool to predict and simulate CO₂ emissions in similar afforested peatlands (e.g. pine and spruce plantations) in temperate maritime climate conditions.

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.