Molecules of these 2 elements are the major constituents of air
... Air Composition ... Gas, Ratio compared to Dry Air (%), Molecular 
Mass - M - ... Sulfur dioxide - SO2 - 1.0 parts/million (ppm); Methane - CH4 - 2.0... [DOC] [TLE] Table of gaseous composition of dry air [PAR] Constituent, Chemical symbol, Mole percent.