Air Composition

Believe it or not Carbon-Dioxide is not the third most abundant gas in the atmosphere. Argon is the third most Abundant gas at just under 1% of the atmosphere composition. 

Image generated by artificial intelligence 

Most of the atmosphere is made of Nitrogen (78%) Oxygen is 20.9 % of the atmosphere. Carbon-Dioxide comprises less than half of one percent of the Earth's atmosphere. 0.04 % to be exact. 

Sources : Wikipedia CO2 article

The Periodic Table by Tom Jackson (paper back)