Routine measurements of air pollutants such as sulphur dioxide, oxides of nitrogen, carbon monoxide and benzene must be performed to fulfil the requirements of the EC Directive on ambient air quality and cleaner air for Europe (Directive 2008/50/EC).
NPL's provides gas standards for calibrating air quality monitors. Mixtures that meet the uncertainty requirements of Directive 2008/50/EC are shown below. Other mixtures may be available on request.
| Component | Matrix gas | Amount fraction range | |
| From | To | ||
| Sulphur dioxide | Nitrogen or air | 100 nmol/mol | 10 mmol/mol |
| Nitrogen monoxide | Nitrogen | 100 nmol/mol | 10 mmol/mol |
| Nitrogen dioxide | Nitrogen or air | 1 µmol/mol | 5 mmol/mol |
| Carbon monoxide | Nitrogen or air | 1 μmol/mol | 500 μmol/mol |
Standards of benzene and other hydrocarbon compounds are also available.
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