This method of air analysis is used for longer term ambient air measurement. Passive diffusion tubes are placed in strategic locations within and around the particular facility being monitored. The tube is opened at one end and to begin the sampling. Over a period of 4 weeks or longer/shorter, depending on the requirement, air is drawn up into the tube and adsorbed onto the material within the tube. Once the required time has elapsed, the cap is closed and the tube is sent for laboratory analysis to determine concentrations of the particular contaminant. Common gases tested for are

Ammonia

Mercaptons

Hydrogen Sulphide

VOC’s