Today we have joined with the Scottish Centre for Indoor Air at Aberdeen University to publish the remarkable figure that “Smoke-free pubs have saved Scots from breathing in over half a tonne of toxic particles”.
So how do we justify such a dramatic claim? Mostly it’s some straightforward arithmetic.
The smoke-free legislation, enacted ten years ago, was accompanied by an unusually thorough evaluation programme. This is why we are so confident of the benefits it has brought.
As part of that programme detailed measurements were carried out on the air quality in pubs before and after the change. Particular emphasis was placed on what we call “PM2.5” – particles smaller than 2.5 millionths of a meter across. See our infographic above to get an idea of just how tiny these particles are. These are important because their small size means they linger in the air for a long time, moving from room to room within a building (so that “smoking rooms” fail for the same reason as non-urinating ends of the swimming pool). They can also penetrate deep into the lungs when breathed in.
We already know that the average adult inhales about 1.0 cubic metre per hour (or 0.017 cubic metres per minute) when they are carrying out ‘light activity’. We have that an average visit to the pub is around 82.2 minutes with an estimated 55.2 visits per year.
That gives an average 75 cubic metres (0.017 * 82 * 55) of pub air inhaled by each adult each year. Hold on to that figure.
The evaluation found that before the smoke-free legislation the average PM2.5 concentration was measured at 246 microgrammes per cubic metre. After the smoke-free legislation came into force, PM2.5 measurements dropped by 86%, so down to 34.4 microgrammes per cubic metre.
To make the comparison over ten years we should allow that the amount of smoke would likely have reduced along with the overall number of smokers. With the 2006 smoking rate being 25.4%, and the average smoking rate between 2007 and 2014 being 23.61%, we can assume a 7% reduction in smoking (assuming no change since the Autumn 2014 survey date of the last figures we have). We can then take an average PM2.5 concentration of 228.69 microgrammes per cubic metre, had the level of smoke in pubs changed at the same rate as the overall smoking rate from 2006.
So the overall reduction achieved by smoke-free public places is 195 microgrammes (229 – 34.4) of PM2.5 for every cubic metre of pub air breathed in.
The number of cubic metres of pub air breathed in over the ten-year period is 75 per year (from above) times ten, so 750 cubic metres. That times 195 microgrammes per cubic metre makes 146,250 (750*195) microgrammes per adult over the ten years. That’s 146 mg each (which is a small mass, but a very large number of particles – remember how small they are?)
With the adult population of Scotland being 4,438,508, and roughly constant over the period, we have a total reduction of PM2.5 of 648,022,000 (146*4438508) mg, which is 648,022 grammes or 648 Kg or well over half a tonne.