Health effects due to changes in air pollution under future scenarios

This chapter predominantly considers effects on health from changes in ambient concentrations of ground level ozone (O3) over the UK. Changes in particulate matter (PM) and nitrogen dioxide (NO2) concentrations are also briefly discussed.

Future concentrations of ground level O3 are difficult to project because of uncertainties in the future emissions in the UK and elsewhere of gases that lead to formation of O3. Uncertainties are compounded when trying to include effects of climate change as well because climate change can impact on many processes that influence ground level O3 concentrations.

Model simulations show that the changes in annual mean ground level O3 over the UK for a +5 C air temperature scenario (+1.0 to +1.5 ppbv, depending on geographic region) are generally smaller than the potential changes in ground level O3 due to emissions changes by 2030 ( 3 to +3.5 ppbv, depending on scenario and geographic region) or due to inter-annual meteorological variability ( 1.5 – 2 ppbv).

UKCP09 projections indicate that temperature increases around +5 C are not anticipated to occur until towards the end of this century, although this is dependent on future greenhouse gas emission trends. An increase in temperature is also only one way in which future climate change will impact on future ground level O3 concentrations. Overall, however, current indications are that until at least mid-century the net additional impact of climate change on the health burden associated with ground level O3 will be smaller than the impact from changes in future anthropogenic emissions.

The extent of adverse health impact attributable to O3 (deaths brought forward and hospitalization) depends markedly on the assumption of a threshold concentration for O3 impacts. Assuming O3 exposure over the full year is relevant, the attributable health impacts assuming a 35 ppbv threshold or a 50 ppbv threshold are, respectively, approximately a factor of 10 lower or approximately a factor 50 lower than those attributable if no threshold is assumed, with the exact ratios varying with the O3 scenarios used.

For the sensitivity experiment with 5 C temperature increase, and with the assumption of no threshold for O3 effect, total UK ozone-related deaths brought forward increase by around 500, or by 4%, on the 2003 baseline mortality of around 11,900. The largest mortality increases are in London, South East and East England and the smallest in Scotland and Northern Ireland. When a threshold for O3 health impact is assumed, there is a proportionally greater increase in total UK ozone-related mortality under the +5 C scenario, but on much smaller absolute numbers: for a 35 ppbv threshold, a 28% increase of around 300 deaths on a baseline of around 1,200; for a 50 ppbv threshold, a 54% increase of around 100 deaths on a baseline of around 200.

There are regional differences in health impacts that vary both with the future scenario assumed and with the O3 threshold used to estimate the impact. This is because of spatial variation in the contribution to O3 concentrations from long-term average O3 and from short-term O3 episodes.