Cooled to -80℃ to remove CO2 and water vapour using absorbent filters
Remaining air cooled to liquify at -200 ℃. Noble gases are removed
Liquid air (NO2 and O2) pumped into fractional column where it is slowly warmed. Remaining components rise and condense in different fractions due to different boiling points
Sources of methane: oil and natural gas, decomposition of vegetation, and waste gases from digestion in animals