Hardly a day goes by without a new study claiming to ‘link’ particulate matter (PM2.5) in outdoor air to deaths or diseases, even from short term exposure.
In short, the answer is ‘Epidemiology,’ which is the study of the distribution and determinants of diseases in populations. It works well when a disease has a single cause like a virus, for example, but it is unable to reliably attribute a single cause to a disease that has multiple potential causes. Air pollution studies do NOT measure the actual exposure of individuals to outside or indoor air. Indeed some studies do not even measure the level of air pollution, they model it instead. Epidemiology relies on statistics in order to try and correlate cause with effect, but one of the principle caveats of science is that ‘correlation isn’t necessarily causation.’ Indeed, margarine consumption in Maine produces a 99% correlation with divorce, but no one believes that margarine is linked to divorce (1).
The ignored ‘elephant in the room’ is the fact that a smoker inhales 10,000 to 40,000 microgrammes per cubic metre of PM2.5 from a single cigarette (2) in a few minutes, which is the equivalent to the PM2.5 inhaled over 50 to 200 days by a non-smoker from outdoor air. (A microgramme is a millionth of a gramme). Smoking cessation studies show that a pack-a-day smoker who gives up after 20 years will have the same 80-year life expectancy as a non-smoker and the same risk of cardiovascular disease at the age of 55 (3), despite inhaling 2kg of PM2.5 over the 20-year period compared to 60g for the 80-year lifetime of a non-smoker. This challenges the claims of deaths from short-term exposure to PM2.5 as well as permanent damage.
The motorised transport-dependent economy is in danger of being further over-regulated and punitively taxed on the basis of soundbite headlines in the media, derived from epidemiological studies, that do not stand up to proper scientific scrutiny. Politicians are only too happy to parrot pseudo-scientific soundbites as justification for CAZ and ULEZ schemes, which massively fail any genuine cost-benefit analysis, taking tens of millions of pounds out of local economies for little or no health benefits in return. Let’s be clear; there is absolutely no scientific evidence linking levels of PM2.5 in outdoor air with deaths or diseases in the UK.
600,000 people die in the UK each year from all causes, which are defined on death certificates and coroners reports. No one dies from air pollution. Since 1970, emissions of PM2.5 have fallen by 79% and Nitrogen dioxide by 72% (4).
A very large peer reviewed study (2017) on California air quality and acute deaths 2000 to 2012 found no association of acute deaths with levels of PM2.5 or ozone (5).
A 2019 peer reviewed paper exposes the bias and flaws in p-values and meta-analysis in papers linking short-term air pollution exposure to heart attacks (6).
25 peer reviewed publications 1995 to 2018 show no association between PM2.5 and mortality (7).
According to the British Heart Foundation, since 1961 the UK death rate from heart and circulatory disease has declined by more than 75%. Death rates have fallen more quickly than the actual number of deaths due to increased life expectancy.
The Committee on the Medical Effects of Air Pollution (COMEAP, 2018) could not unanimously link NO2 to mortality (8).
Notes for Editors
(1) Spurious correlations: Margarine linked to divorce?https://www.bbc.co.uk/news/magazine-27537142
(2) National Research Council. Environmental tobacco smoke: measuring exposures and assessing health effects. Washington, D.C.: National Academy Press; 1986.
(3) New smoking cessation study (2018) debunks EPA’s PM2.5 death claims:
(4) Emissions of air pollutants in the UK, 1970 to 2017:
(5) Air quality and acute deaths in California, 2000 – 2012:
(6) Evaluation of meta-analysis of air quality and heart attacks, a case study (2019):
(7) Negative studies on PM2.5 and mortality:
(8) COMEAP (2018):