Impact of methane and other precursor emission reductions on surface ozone in Europe: Scenario analysis using the EMEP MSC-W model

Abstract. The impacts of future methane (CH₄) and other precursor emission changes are investigated for surface ozone (O₃) in the United Nations Economic Commission for Europe (UNECE) region excluding North America and Israel (the "EMEP region", for European Monitoring and Evaluation Programme) for the year 2050. The analysis includes a Current Legislation (CLE) and Maximum Feasible Technical (MFR) reduction scenario, and a scenario that combines MFR reductions with an additional dietary shift that also meets the Paris Agreement objectives with respect to greenhouse gas emissions (LOW). For each scenario, background CH₄ concentrations are calculated using a probabilistic Earth System model emulator, and combined with other precursor emissions in a three-dimensional Eulerian chemistry-transport model. While focus is placed on peak season maximum daily 8-hour average (MDA8) O₃ concentrations, a range of other indicators for health and vegetation impacts are also discussed. Our analysis show that roughly one-thirds of the total peak season MDA8 reduction achieved between the 2050 CLE and MFR scenarios is attributable to CH₄ reductions, resulting predominantly from CH₄ emission reductions outside of the EMEP region. The impact of other precursor emission reductions is split nearly evenly between the reductions inside and outside of the EMEP region. However, the relative importance of CH₄ and other precursor emission reductions is shown to depend on the choice of O₃ indicator, though indicators sensitive to peak O₃ show generally consistent results. The analysis also highlights the synergistic impacts of CH₄ mitigation as reducing solely CH₄ achieves, beyond air quality improvement, nearly two-thirds of the total global warming reduction calculated for the LOW scenario compared to the CLE case.