A perfectly dry troposphere refers to the air having no water vapor. Water vapor is the most variable gas in the air and it ranges from near 0% to around 4%. When water vapor is not considered, there is a fairly fixed percentage for each of the most abundant gases in the troposphere. These three most abundant gases are Nitrogen, Oxygen and Argon. Rounded to the nearest percent, the troposphere has the following makeup when water vapor and trace gases are ignored: Nitrogen: 78% Oxygen: 21% Argon: 1% |