DOAS Technology

Paul Boughton

Differential optical absorption spectroscopy (DOAS) is based on transferring a beam of light from a high-pressure xenon lamp, including both the visible spectrum, ultraviolet and infrared wavelengths, over a chosen path and then using advanced computer calculations to evaluate and analyse the light losses from molecular absorption along the path.

Because every type of molecule, every gas, has its own unique absorption spectrum properties, or 'fingerprint', it is possible to identify and determine the concentrations of several different gases in the light path at the same time.

The DOAS technology is commonly used in ambient air quality monitoring (AQM), where paths of several hundred metres can be monitored at very low concentrations. The same technology is used for process and emission monitoring (CEM) applications, where an emitter and receiver is typically placed directly on stack or a duct/pipe. The light is captured by a receiver and conducted through an optical fibre to the analyser. The fibre allows the analyser to be installed away from potentially aggressive environments and no part of the system is ever in direct contact with the process environment as an air buffer is used to protect the emitter and receiver. This makes the system extremely reliable, robust and durable over time.

One analyser can be connected to multiple paths through an optical switch (multiplexer) and hence monitor several paths in parallel.

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Opsis AB is based in Furulund, Sweden.

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