# Why do all heavier gases in the atmosphere not settle down to the surface? [duplicate]

Some pollutants heavier than air that are released into the atmosphere include $$\text{CO}_2,\text{SO}_2,\text{SO}_3,\text{NO}_2$$ etc. Since these gases are heavier than air, Why do they not settle down closer to the surface? By that, I mean why is the concentration of these gases not maximum at sea level?

This article has been used as a reference: it is evident that the $$\text{CO}_2$$ concentration around the 200 HPa band is more than the 800 HPa band in the month of July. Note that this article also does not provide clarity on surface $$\text{CO}_2$$ levels, it gives data for the 5 km-25 km altitude range.