I noticed that a person, middle aged, was carrying heavy grocery bags while walking and I remembered something from my past. From time to time because a city is very industrial, I would do the same thing. And sometimes because there's pollution from an old car or a factory or tobacco smoke I would breathe some of it in. It's not a major problem but may weaken the population maybe 5% by the time they reach old age. Of course -I was a teenager and am still young so I have my youth strength. It's not such a large problem but maybe people could find a solution. I think this is why it's important to make plants and trees. When I was a teenager it used to be one tree, fenced in, small size, but it's been a decade and a half and they've grown larger. The only thing I can add in to this of value from my experience in Bulgaria -I think a pine tree produces the most oxygen because of its size. (Theres a nice place in astoria near a market where there are four of them.)