-As Bob Ross said, the Ozone layer keeps the heat in. But this only aids in "Global Warming", and it is not an air pollutant.
-Also, Carbon Monoxide is not abundant enough to be considered a main air pollutant.
As we know, burning Octane (gasoline in cars) we are left with a byproduct in the combustion reaction which is Carbon Dioxide. Carbon dioxide is a gas at room temperature, but it is more dense than the oxygen and nitrogen in our atmosphere. Carbon Dioxide is poisonous to humans (that's why we exhale it from our bodies).
Another air pollutant is Sulfur. Long story short, when we mine for coal, sulfur deposits are released into the air. This sulfur reacts during lightning storms to create low amounts of acid. This acid then falls as "acid rain" harming structures and wildlife over time.