Preparation and analysis of zero gases for the measurement of trace VOCs in air monitoring

Air quality observations are performed globally to monitor the status of the atmosphere, its level of pollution and to assess mitigation strategies. Regulations of air quality monitoring programmes in various countries demand high precision measurements for harmful substances often at low trace concentrations. These requirements can only be achieved by using high quality calibration gases including high purity zero gas. For volatile organic compound (VOC) observations, zero gas is defined being hydrocarbon free like purified air, nitrogen or helium and is essential for the characterisation of the measurement devices and procedures, for instrument operation as well as for calibrations. Two commercial and one self-built gas purifiers were tested for their removal efficiency of VOCs following a standardised procedure. The tested gas purifiers included one adsorption cartridge with an inorganic media and two types of metal catalysts. A large range of VOCs was investigated including the most abundant species typically measured at air monitoring stations. Both catalysts were able to remove a large range of VOCs whilst the tested adsorption cartridge was not suitable to remove light compounds up to C 4 . Memory effects occurred for the adsorption cartridge when exposed to higher concentration. This study emphasises the importance to explicitly examine a gas purifier for its intended application before applying in the field.