Health burdens of surface ozone in the UK for a range of future scenarios

Exposure to surface ozone (O₃), which is influenced by emissions of precursor chemical species, meteorology and population distribution, is associated with excess mortality and respiratory morbidity. In this study, the EMEP-WRF atmospheric chemistry transport model was used to simulate surface O₃ concentrations at 5km horizontal resolution over the British Isles for a baseline year of 2003, for three anthropogenic emissions scenarios for 2030, and for a +5°C increase in air temperature on the 2003 baseline. Deaths brought forward and hospitalisation burdens for 12 UK regions were calculated from population-weighted daily maximum 8-hour O₃. The magnitude of changes in annual mean surface O₃ over the UK for +5°C temperature (+1.0 to +1.5ppbv, depending on region) was comparable to those due to inter-annual meteorological variability (-1.5 to +1.5ppbv) but considerably less than changes due to precursor emissions changes by 2030 (-3.0 to +3.5ppbv, depending on scenario and region). Including population changes in 2030, both the 'current legislation' and 'maximum feasible reduction' scenarios yield greater O₃-attributable health burdens than the 'high' emission scenario: +28%, +22%, and +16%, respectively, above 2003 baseline deaths brought forward (11,500) and respiratory hospital admissions (30,700), using O₃ exposure over the full year and no threshold for health effects. The health burdens are greatest under the 'current legislation' scenario because O₃ concentrations increase as a result of both increases in background O₃ concentration and decreases in UK NO_x emissions. For the +5°C scenario, and no threshold (and not including population increases), total UK health burden increases by 500 premature deaths (4%) relative to the 2003 baseline. If a 35ppbv threshold for O₃ effects is assumed, health burdens are more sensitive to the current legislation and +5°C scenarios, although total health burdens are roughly an order of magnitude lower. In all scenarios, the assumption of a threshold increases the proportion of health burden in the south and east of the UK compared with the no threshold assumption. The study highlights that the total, and geographically-apportioned, O₃-attributable health burdens in the UK are highly sensitive to the future trends of hemispheric, regional and local emissions of O₃ precursors, and to the assumption of a threshold for O₃ effect.