Which are most of the gas molecules in the atmosphere found?

Most of the gas molecules in the atmosphere are concentrated in the troposphere, the lowest layer of Earth's atmosphere, extending from the surface up to about 8 to 15 kilometers (5 to 9 miles) high. This layer contains approximately 75% of the atmosphere's mass and is where weather occurs. The primary gases present are nitrogen (about 78%) and oxygen (about 21%), along with trace amounts of argon, carbon dioxide, and other gases.