Environmental authorities continuously measure air quality. A network of measurement stations records the concentration of pollutants such as sulfur dioxide, nitrogen oxides, carbon monoxide, ozone, benzene and particulates. To ensure that the instruments used supply reliable and comparable values, they must be calibrated. That task is handled by accredited laboratories that also stock the reference materials required for calibration. During calibration, the measured values are compared to gases of known composition. That process uses a high-purity zero gas and a calibration gas with precisely defined composition.
AIR QUALITY MONITORING
Recording pollutants precisely