Future air pollution related health burdens associated with RCP emission changes in the UK

Three Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) are used to simulate future ozone (O 3 ), nitrogen dioxide (NO 2 ), and fine particulate matter (PM 2.5 ) in the United Kingdom (UK) for the 2050s relative to the 2000s with an air quality model (AQUM) at a 12 km horizontal resolution. The present-day and future attributable fractions (AF) of mortality associated with long-term exposure to annual mean O 3, NO 2 and PM 2.5 have accordingly been estimated for the first time for regions across England, Scotland and Wales. Across the three RCPs (RCP2.6, RCP6.0 and RCP8.5), simulated annual mean of the daily maximum 8-h mean (MDA8) O 3 concentrations increase compared to present-day, likely due to decreases in NO x (nitrogen oxides) emissions, leading to less titration of O 3 by NO. Annual mean NO 2 and PM 2.5 concentrations decrease under all RCPs for the 2050s, mostly driven by decreases in NO x and sulphur dioxide (SO 2 ) emissions, respectively. The AF of mortality associated with long-term exposure to annual mean MDA8 O 3 is estimated to increase in the future across all the regions and for all RCPs. Reductions in NO 2 and PM 2.5 concentrations lead to reductions in the AF estimated for future periods under all RCPs, for both pollutants. Total mortality burdens are also highly sensitive to future population projections. Accounting for population projections exacerbates differences in total UK-wide MDA8 O 3 -health burdens between present-day and future by up to a factor of ~3 but diminishes differences in NO 2 -health burdens. For PM 2.5, accounting for future population projections results in additional UK-wide deaths brought forward compared to present-day under RCP2.6 and RCP6.0, even though the simulated PM 2.5 concentrations for the 2050s are estimated to decrease. Thus, these results highlight the sensitivity of future health burdens in the UK to future trends in atmospheric emissions over the UK as well as future population projections.