Are you really comparing the relationship between smoking and lung cancer with a relationship between air pollution (especially outdoor) and heart disease? Seriously, they're not even in the same ballpark in terms of objective statistical significance. Not even close.
You may not be able to say with absolute 100% certainty that "a specific smoker got long cancer from smoking", but you can often be >95% certain. Can you (or anyone) say the same for outdoor air pollution and heart disease?
Don't move the goal post. If a very large populationa has 20%X vs 30%X, then only 1/3 of the cases are Caused by _. But, the difference is still very significant.
Again your example isn't even in the same ballpark as what you'd actually see in a rigorous study of the relationship between outdoor air pollution and heart disease, so please stop implying that it's somehow "very significant."
As mentioned in another comment, many of those studies are referring to indoor air pollution (or including indoor and outdoor air pollution in the same study), which is disingenuous at best.
I'm not calling into question the method of action, but I am saying that there is no evidence of outdoor air pollution having anywhere close to the same effect on premature death (via heart disease or otherwise) as smoking, nor would it even be remotely close to the other fictitious numbers you've mentioned.
Smoking on it's own causes ~6 million deaths per year and air pollution is linked to ~5.5 to 7 million deaths a year so they really are on the same scale. (And larger than my example 20% vs 30%.)
Yes, only a subset of the population smoke so the direct impact is higher. However, some areas also have vastly higher levels of air pollution.
Now, if you have some actual evidence then sure feel free to share, but I am just not hearing it.
Again, you're conflating indoor and outdoor air pollution, and if you look closely, even the WHO's own "facts" for estimates of outdoor/ambient air pollution deaths are full of weasel words and misleading claims.
Instead of merely reading the conclusions of these studies, I'd encourage you to look at the underlying data with a healthy dose of skepticism. Only then will you start to see all the holes in the research.
In door air pollution includes outdoor air pollution as most people don't have much in the way of air filtration. So, they are not exactly separate categories independent of each other.
You even have edge cases like parking lot attendants / toll collectors who have vastly increased disease risks.
You may not be able to say with absolute 100% certainty that "a specific smoker got long cancer from smoking", but you can often be >95% certain. Can you (or anyone) say the same for outdoor air pollution and heart disease?