SCHEDULE 4MEASUREMENTS OF OZONE PRECURSOR SUBSTANCES
Objectives
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 emissions inventories and to help attribute emission sources to pollution concentration.
An additional aim is to support the understanding of ozone formation and precursor dispersion processes, as well as the application of photochemical models.
Substances
Measurements of ozone precursor substances must include at least nitrogen oxides, and appropriate volatile organic compounds (VOCs). A list of VOCs recommended for measurement is given below.
| 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 |
Reference methods
The reference method for the analysis of oxides of nitrogen shall be that specified in Part II of Schedule 6 to the Air Quality Limit Values Regulations (Northern Ireland) 2002, (S.R.2002/94).
Siting
Measurements should be taken in particular in urban and suburban areas at any monitoring site set up in accordance with the requirements of the Air Quality Limit Values Regulations (Northern Ireland) 2002 and considered appropriate with regard to the monitoring objectives in this Schedule.