Air pollution has been linked to respiratory and cardiovascular diseases, as well as dementia including Alzheimer’s disease. One way to quantify the impact on health is to compare pollution levels with demographic data. While the methodology to calculate this is complicated, it gives an estimated number of deaths attributable to air pollution.

In the 2014 Public Health England report Estimating Local Mortality Burdens associated with Particulate Air Pollution, a study of PM2.5 pollution, estimated the number of attributable deaths (aged 25+) as 95 per year in Portsmouth. This accounts for 5.9% of caused deaths and an associated 1059 life-years lost each year. While this figure has been quoted as the total number of deaths caused by air pollution, such as in the Portsmouth Public Heath Annual Report 2016, this does not account for pollution from other sources such as NO2.

The added effect of other pollutants was addressed in the 2016 report Every breath we take by the Royal College of Physicians. They estimate 40,000 deaths a year nationally. “The Committee on the Medical Effects of Air Pollutants (COMEAP) estimates 29,000 ‘equivalent’ deaths annually from exposure to PM 2.5 in the UK, with only a small fraction of that figure relating to exposures to concentrations in excess of legal limits. This figure increases to around 40,000 if the recently described effects of NO 2 are taken into account.” This corresponds to 130 deaths a year in Portsmouth, so the Public Health report is probably underestimating the risk. (Other reports estimate 50000 deaths/year nationally).

However, not everyone is convinced the NO2 estimate is reliable. Anthony Frew, a Professor of Allergy & Respiratory Medicine, stated that “The extra 11,000 deaths is speculation. My reading is that there is no proof. People don’t really understand if the effects on health are the result of NO2 or from other pollutants that come from the same sources.” In short, the exact health burden is still under investigation.

It is important to remember that air pollution health burdens are a statistical tool. People generally don’t die from air pollution alone. There are not literally 40,000 people with air pollution on their death certificate. The health burden is really a shortening of many peoples lives, along with poor health and societal costs associated with that. Flew points out “The public discussion has shorthanded the whole issue. There is loss of life from air pollution but the discussion of deaths isn’t helpful – we should be talking about the impact on people’s lives”. We can loosely use these statistical tools as a rough measure of the relative risk to public health, while remembering not to misinterpret what the numbers actually mean.

Postscript: I’ve seen a figure of 600 early deaths per year in Portsmouth cited by the former director of public health but I have no information about the methodology or original source for this number. If anyone knows, please get in touch!