To give some idea how daft the BBC Reality Check team's claim is that man-made PM2.5 air pollution in the UK is shortening lives by 11.5 years, compare it with the lifetime reductions that are quoted for smoking (this is active smoking, not passive smoking). There was a long-term study carried out in the Netherlands called "the Zutphen Study".
In this study, the average lifetime reduction was found to be 6.8 years for cigarette smoking in general, 8.8 years for heavy cigarette smoking (heavy smoking seems to be defined as smoking over 30 cigarettes per day in the paper), and 4.7 years for pipe or cigar smoking. So the BBC is claiming that breathing in modern day PM2.5 air pollution in the UK is more dangerous than smoking.
As noted in the previous post, academics tend to quote the lifetime reduction for man-made PM2.5 air pollution in months, that is 3 to 4 months for Scotland and Northern Ireland, 6 to 7 months for England and Wales, and 9.5 months for the London area. But even these figures, that are in the order of months, could be regarded as over the top, if you consider an argument put forward by Junkscience.com's Steven Milloy:
Milloy's argument is that a smoker inhales substantially more PM2.5 from cigarettes than a non-smoker breathing in polluted outdoor air. But cigarette smokers are advised by health authorities that if they give up smoking, they will recover most, if not all, of their 'lost lifetime' that they would have incurred if they had carried on smoking. Otherwise there is little point in advising people to give up smoking. But a person who has quit smoking may have taken in a much higher accumulated 'dose' of man-made PM2.5 in their years of smoking than the non-smoker will pick up from air pollution in a lifetime.