The UK independent expert committee, the Committee on the Medical Effects of Air Pollutants (COMEAP), released a report on quantifying the health impacts associated with exposure to NO2 and PM2.5 air pollutants, the two pollutants most relevant to human health. Combustion engine emissions are a significant source of both these pollutants and their impacts on health are very closely related and difficult to separate.
The evidence for the effects of PM2.5 is clearer than that for NO2. Earlier COMEAP reports assessed the health effects of PM2.5 (alone) in terms of excess or attributable mortality. The evidence for the effects of NO2 alone on human health is less clear than that for particulate pollution, so interpreting the scientific evidence on NO2 has proved to be a challenging task for COMEAP. This new report therefore addresses public health impacts in terms of attributable mortality linked to NO2 exposure alone as an air pollutant and NO2 in combination with PM2.5. COMEAP was not however able to come to a unanimous view regarding the conclusions drawn from the scientific evidence. As a result, the report presents a majority committee view and the views of a dissenting group who did not support the majority conclusions. The report explains the reasons for the differences of expert opinion.
COMEAP concluded that, overall, the impact of NO2 with PM2.5 was equivalent to an increase in deaths of 28,000 to 36,000 in the UK. These numbers are not figures for the actual deaths recorded as being due to air pollution in the UK. They are estimates only of the number of deaths that air pollution could cause, if air pollution was the sole cause of death in those people. Air pollution is rarely if ever the sole cause of death so these figures are potentially misleading especially when reported in the press as deaths actually caused by air pollution.
COMEAP also quote a lower range of an excess of 16,000 to 19,000 equivalent deaths associated with NO2 exposure. The difference in the two sets of estimates relates to variation in scientific expert confidence in the use of the published research data, which was one of the areas where the expert committee was most divided.
COMEAP provide an alternative explanation for the scale of the health impacts, i.e. for a sustained reduction in NO2 of 1 μg/m3 and for all other traffic related pollutants over the next 106 years, the average life expectancy in the UK would increase by around eight days. For a reduction in NO2 of 1 μg/m3 alone, then the increase in average life expectancy in the UK would be around two to five days. This may be an easier metric to understand for some.
It is not possible within the constraints of this short item to give a full briefing on the COMEAP report and its conclusions; this will be provided on the Health Protection Scotland (HPS) website in due course.
The report is available to view in full or as a summary.