Greenhouse gasses are kinds of gasses that has the ability to absorb and hold heat that can be released in different directions. If a greenhouse gas is present in the earths crust, it will significantly increase the average surface temperature of the earth. Examples of greenhouse gasses are water vapor, methane, nitrous oxide and ozone.
Ozone in the troposphere level can block the harmful ultraviolet rays that can penetrate the earth. This should not confuse you, ozone is very useful in the troposphere but NOT between the earth's surface and stratosphere. Between those areas, ozone is capable to absorb heat 3000 times as much as what CO2 can do.
We can simply state it this way: ozone is beneficial in the ozone layer, other than that, it is a threat. It is considered a pollutant to a place where is should not be present. And by the way, it is poisonous when inhaled.