Regulation 18
1. The main objectives of measurements of ozone precursor substances are to analyse any trend in ozone precursors, to check the efficiency of emission reduction strategies, to check the consistency of emission inventories and to help attribute emission sources to pollution concentration.
2. An additional aim is to support the understanding of ozone formation and precursor dispersion processes, as well as the application of photochemical models.
3. Measurements of ozone precursor substances shall include at least nitrogen oxides, and appropriate volatile organic compounds. For the purposes of this Schedule, “volatile organic compounds” means all organic compounds from anthropogenic and biogenic sources, other than methane, that are capable of producing photochemical oxidants by reaction with nitrogen oxides in the presence of sunlight.
4. The Scottish Ministers shall, in particular, consider measuring the following volatile organic compounds–
| Ethane | 1-Butene | Isoprene | Ethyl benzene |
| Ethylene | trans-2-Butene | n-Hexane | m+p-Xylene |
| Acetylene | cis-2-Butene | i-Hexane | o-Xylene |
| Propane | 1.3-Butadiene | n-Heptane | 1,2,4-Trimeth. benzene |
| Propene | n-Pentane | n-Octane | 1,2,3-Trimeth. benzene |
| n-Butane | i-Pentane | i-Octane | 1,3,5-Trimeth. benzene |
| i-Butane | 1-Pentene | Benzene | Formaldehyde |
| 2-Pentene | Toluene | Total non-methane hydrocarbons |
5. The reference method for the analysis of oxides of nitrogen shall be ISO 7996:1985, Ambient air – determination of the mass concentrations of nitrogen oxides – chemiluminescence method.
6. Measurements shall be taken in particular in urban and suburban areas at any monitoring site considered appropriate with regard to the objectives set out in this Schedule.