Then in the 1890's, the Scottish chemist William Ramsay discovered that air also contained minute traces of other gases that are very slow to react with other chemicals. These inert gases include argon, helium, krypton, xenon, neon, and radon. Depending upon the geographic location, air contains differing levels of pollutants like carbon dioxide and dust. Carbon dioxide plays an important role in the lives of plants and animals. Small particles of dust are light enough to be held up by the air.
Volcanic eruptions contribute to the dust level in the air.
Humans contribute to the pollution level by pumping soot and harmful gases produced by vehicles and industries into the air. NASA's Mission to Planet Earth seeks to understand how all of Earth's systems affect each other, including how air pollution affects the ozone layer. Whether bird, balloon, or aircraft, things that fly make use of certain important characteristics of air to stay aloft. Most air molecules reside in the lower atmosphere. Air expands when warmed and contracts when cold.