Sensitive, Simultaneous Gas Measurement

Sensitive, Simultaneous Gas Measurement


Emissions from interior design and construction materials are a common cause of indoor air problems. Ammonia and formaldehyde are some of the most critical chemicals for air quality. The most typical sources of formaldehyde and ammonia in indoor air are ceiling and wall leveling compounds, adhesives and plastic mats, and particularly the adhesives and solvents used in them. In Finland the limit value for indoor air gas content that does not cause observable health hazards are around 20–30 ppb for ammonia (30–40 µg/m³), and around 40–125 ppb for formaldehyde (30–100 µg/m³), depending on the indoor climate class.

Timo Rajamäki and colleagues, VTT, Finland, have developed a real-time device that measures the concentrations of several gases reliably and continuously with a sensitivity of less than 10 ppb. The prototype can be modified for different purposes. It can, for example, be used to measure ammonia and formaldehyde concentrations simultaneously in indoor air. This is impossible with the meters currently in use. It can also be used to measure emissions reducing outdoor air quality in city centers.

The computer-controlled device sucks the gas to be measured using its own sampling pump. The measurement of the device is based on direct laser absorption with cavity enhancement employing fundamental vibration level excitations of ammonia and formaldehyde molecules. Light travels through the measured air in a multireflection cuvette, achieving several tens of meters of measurement distance and a sufficient sensitivity even with small concentrations.


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