| Concentration | Molecules |
| percentage | oxygen, water, carbon dioxide |
| parts-per-million | acetone, carbon monoxide, methane, hydrogen, isoprene, benzenemethanol |
| parts-per-billion | formaldehyde, acetaldehyde, 1-pentane, ethane, ethylene, other hydrocarbons, nitric oxide, carbon disulfide, methanol, carbonyl sulfide, methanethiol, ammonia, methylamine, dimethyl sulfide, benzene, naphthalene, benzothiazole, ethane, acetic aide |