How do scientists separate the various molecules of gases in the atmosphere?

Question

How do scientists know that the atmosphere is composed of this percent of hydrogen and this percent of oxygen and so on?

Answer 1

To figure out the percentages of each gas in the air, scientists can use a machine called a GCMS, which is an abbreviation for "Gas Chromatography Mass Spectrometer." It consists of two parts: the gas chromatograph, and the mass spectrometer.

The gas chromatograph separates the sample of air into each of it's separate components. It is basically a long tube packed with a very very fine material. Some gasses "stick" to this material more so than others, so that at the end of the tube, the gas that stuck to it the least comes out first, and the gas that stuck to it most comes out last.

As it comes out of the tube, each gas enters the mass spectrometer, which can tell the molecular weight of each gas (so if it said the weight was 32, it would be oxygen; if 28 it would be nitrogen, and so on). It shows the mass of each one as a peak, and the relative heights of each peak can tell you the ratio of one gas to another. So, if the peak for oxygen was 1/4 as intense as the peak for nitrogen, you could say that the sample was 20% O2 and 80% N2.

That's a pretty simplistic view of the process, but I hope it helps answer your question!

Answer 2

The Earth spins, kind of like a centrifuge. This constant centripetal force causes the gasses to separate spontaneously. Most all O2 is found within 7 feet of the Earth's surface. All O3 (ozone) makes its way to the ozone layer. They then measure the zones known to be occupied by a certain gas. Hydrogen and Oxygen do what is called the trick of life. If O3 weren't able to rise passed the H2 and O2 stay true to its heavier nature life could not exist. Oxygen is the only gas with two measurable zones of concentration. The first is the ozone. The second is the biosphere or life zone.

Answer 3

They submit it to controlled chemical reactions and, for example, measure how much oxidation takes place. They run it through water and measure some of the gasses dissolved in the water. They refrigerate it, and separate out the elements and molecules which liquefy at different temperatures. That covers most of it.