Table 2. Volatile organic compounds measured by ion-molecule reaction-mass spectrometry, with indications on whether molecules were directly or indirectly calibrated, and which molecules were included in the regression models after comparison between environmental air and exhaled air samples.

Measured molecules (97)	Directly calibrated molecules (23)	Indirectly calibrated molecules* (8)	Molecules included in models (81)
CH4—Methane		x	x
C2H2—Acetylene	x		x
M27
M29			x
C2H6—Ethane	x
CH2O—Formaldehyde	x
CH4O—Methanol	x
C2H3N—Acetonitrile	x		x
N2O—Nitrous Oxide		x	x
CH2O2—Formic Acid	x
HNO2—Nitrous Acid		x	x
SO2—Sulfur Dioxide		x
H2O—Water		x
O2—Oxygen	x
CO2—Carbon Dioxide	x
NH3—Ammonia		x	x
M19			x
C2H4—Ethylene	x		x
NO–Nitric Oxide		x
M31
M32
M33			x
H2S—Hydrogen Sulfide		x
C3H6—Propene	x		x
M43			x
C2H4O—Acetaldehyde	x		x
M45			x
M48
M49
C4H6—Butadiene	x		x
C4H10O—Butanol	x		x
C4H8O—Methyl Ethyl Ketone	x		x
C3H6O—Acetone	x		x
C3H8O—n-Propanol	x		x
C2H4O2—Acetic Acid	x		x
M60			x
M61			x
M62			x
M63			x
M66			x
M67			x
C5H8—Isoprene	x		x
M69			x
M70			x
M71			x
C5H12—n-Pentane	x		x
M73			x
M74			x
M75			x
M76			x
M77			x
C6H6—Benzene	x		x
M79			x
M80
M81			x
M82			x
M83			x
M84			x
M85			x
C6H14—n-Hexane	x		x
M87			x
M88			x
M89			x
M90			x
M91			x
C7H8—Toluene	x		x
M93			x
M94			x
M95			x
M96			x
M97			x
M98			x
M99			x
C7H16—n-Heptane	x		x
M101			x
M102			x
M103			x
M104			x
M105			x
M106			x
M107			x
M108			x
M109			x
M110			x
M111			x
M112			x
M113			x
M114			x
M115			x
M116			x
M117			x
M118			x
M119			x
M120			x
M121			x
M122			x
M123			x

* Calibrated through Benzene