From Continental to Street Scales: Climate Change Impacts on Atmospheric Composition over Europe and London

Abstract. Climate change will impact ozone (O₃) and fine particulate matter (PM_2.5) through its influence on natural emissions, atmospheric chemistry, deposition and transport. A coupled modelling approach is employed to identify the key processes and determine how regional air pollution across Europe and urban-scale air quality in London in the 2090s are impacted by climate change under Representative Concentration Pathway (RCP)8.5. Climate change projections from the HadGEM2-ES Earth System Model nudge the nested WRF-EMEP4UK model, which drives the street-scale ADMS-Urban model. Annual-mean temperature increases exceeding 4 °C produce substantial increases in summer biogenic isoprene emissions. There is a strong contrast in summer and winter-mean O₃ responses to climate change, with large summer increases over southern Europe (≤ 10 ppbv) and winter decreases over Europe. Annual-average PM_2.5 concentrations are elevated (5–10 µgm^-3) over most of Europe, also driven by higher isoprene emissions that promote secondary organic aerosol formation. Decreases in primary and inorganic PM_2.5 components are prominent in winter. The seasonality of urban air pollution is modified over London under climate change: the O₃ peak amplitude is reduced, whilst the winter peaks in PM_2.5 and NO₂ are more pronounced, with nighttime increases. The diurnal profile of urban air pollution typically flattens. Climate-induced changes in O₃ aid attainment of long-term air quality guidelines in northern Europe, but pose challenges elsewhere. Achieving long-term PM_2.5 guidelines over much of Europe becomes increasing difficult with climate change, while attaining short-term air quality guidelines in London remains a major challenge, especially for NO_2.