filtration through your undewear if it is noxious gases.
Sorry, I am not very scientifically minded and that was a typical response from my hubby if I were to ask him the same question. rofl
Guess similar way to water, by using a certain chemical process to attract that certain gas to a jar 9or conical flask if you want to be correct). So maybe by burning a match you make all the oxygen rush to that point and trap it 9before itmburns up obviously).
Air is compressed and cooled until it liquefies and then it is distilled off fraction by fraction as all the liquid gases have different boiling points.