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

Highlights: • NO_x emissions decrease in 2050s compared to 2000s across the UK for all RCPs. • Across the RCPs, O₃ concentrations in 2050s increase compared to present-day. • Annual mean NO₂ and PM_2.5 concentrations decrease under all RCPs for the 2050s. • Total mortality burdens are highly sensitive to future population projections. • The PM_2.5 composition changes in 2050s compared to present-day. Three Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) are used to simulate future ozone (O₃), nitrogen dioxide (NO₂), 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 O₃, NO₂ 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) O₃ concentrations increase compared to present-day, likely due to decreases in NO_x (nitrogen oxides) emissions, leading to less titration of O₃ by NO. Annual mean NO₂ and PM_2.5 concentrations decrease under all RCPs for the 2050s, mostly driven by decreases in NO_x and sulphur dioxide (SO₂) emissions, respectively. The AF of mortality associated with long-term exposure to annual mean MDA8 O₃ is estimated to increase in the future across all the regions and for all RCPs. Reductions in NO₂ 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 O₃-health burdens between present-day and future by up to a factor of ~3 but diminishes differences in NO₂-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.