However lead and one or two other heavy metals have been carried by airborne pollution in the past and no doubt pose a threat alongside cadmium and several others at the present. Also present in the air are other solid particles, carbon being major among them. The health of humans is directly affected by such particles, but our remit here is less noticeable events. Photosynthesis is a feature process of all of our green plants we don't eat without photosynthesis. If masked by carbon or other deposits, plant leaves cannot operate and produce no carbohydrate. That means death, as it did when asteroids almost cut off this lifeline for years at a time in the past. Huge extinctions are a feature of the Earth's past, and this kind of air pollution seems mainly responsible. The Sun was blocked out, which was a major cause for deaths, but deposits on leaves could equally have caused a food chain failure when deposits covered the sky and the ground.
It is perhaps at the finale that we should add another of the less obvious, more insidious air pollutants. The POPs are volatile but relatively insoluble, hitching a ride on solid particles to travel enormous distances to countries that have never produced them. They are of course the Organic Pollutants that Persist in the environment. Their main feature is their toxicity, with even some carcinogenic properties, but there are a vast range of them from PCBs to Agent Orange. Their effects may still be very much in the environment but awareness of their presence in animal fats (many being fat soluble) is leading to a small decrease in their known effects on humans.
Other air pollution events have included CFCs (chlorofluorocarbons). They were used in fridges, but discarded when the ozone in the atmosphere was destroyed by them. Ozone is strategic in preventing ultraviolet light from entering the atmosphere and causing big increases in mutation rates. The legacy of the CFC pollution is our commitment to watching the two ozone holes at the Earth's poles, in case any gases start affecting their size again! There are many such candidates in air pollution.
Read more at http://www.earthtimes.org/encyclopaedia/environmental-issues/air-pollution/#2sEZ371WSvhzy73b.99