During the industrial revolution, there was little awareness of quite how much damage could be done to healthy people's lungs by pollution - largely because we'd never had it on such a huge scale before. But we have known for a long time that clean air is good for the lungs - after all, people with 'consumption' (tuberculosis) used to be sent to the mountains to breathe the fresh air.
This is a companion discussion topic for the original article at https://patient.info/features/chest-lungs/this-is-why-air-pollution-is-so-dangerous-for-your-lungs