for me, hands down and no doubt , it is tree pollens and then pretty much the gamut that attack me.  there are millions of people with seasonal allergies - not urban center allergies.  that's not to say that bad polluted air is not bad for you and deadly for some.  asthma has  made a huge grow in the last 15 years or so.  black mold is toxic. ++  my view on us becoming animals due to car caused climate change?  we are animals that right now are on top because of certain conditions. those conditions change enough  - we struggle, perhaps to the point to extinction or almost extinction.  it is the cycle of earth's life - ask the dinosaurs.  they pretty much ruled and poof.  they went fast too, in a relatively short time.  birds are their descendants..look at them and their pelvic area ...tiny t rex hip/leg thing..  our future, if any, ?  anyway, we are destined as human beings to fall at some point. maybe we are close to it and it's climate  change driven. it what it is.