Measurement of ozone precursor substances shall include at least nitrogen oxides (NO and NO2), and appropriate volatile organic compounds (VOC). A list of volatile organic compounds recommended for measurement is given below:
| 1-Butene | Isoprene | Ethyl benzene | |
|---|---|---|---|
| Ethane | Trans-2-Butene | n-Hexane | m + p-Xylene |
| Ethylene | cis-2-Butene | i-Hexane | o-Xylene |
| Acetylene | 1,3-Butadiene | n-Heptane | 1,2,4-Trimethylebenzene |
| Propane | n-Pentane | n-Octane | 1,2,3-Trimethylebenzene |
| Propene | i-Pentane | i-Octane | 1,3,5-Trimethylebenzene |
| n-Butane | 1-Pentene | Benzene | Formaldehyde |
| i-Butane | 2-Pentene | Toluene | Total non-methane hydrocarbons |