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We describe a simple method for detecting formaldehyde using low resolution non-dispersive UV absorption spectroscopy. A two channel sensor was developed, making use of a strong absorption peak at 339 nm and a neighboring region of negligible absorption at 336 nm as a reference. Using a modulated UV LED as a light source and narrow laser-line filters to select the desired spectral bands, a simple detection system was constructed specifically targeted at formaldehyde. By paying particular attention to sources of noise, a minimum detectable absorbance of 5&#x00D7;10-5 absorbance units (AU) was demonstrated with a 20 s averaging period (as &#x0394;I/I0). The system was tested with formaldehyde finding a limit of detection of 4.3 ppm for a 195 mm gas cell. As a consequence of the low gas flow rates used in our test system, a time period of over 8 min was used in further tests, which increased the minimum detectable absorbance to 2 &#x00D7; 10-4 AU, 17 ppm of formaldehyde. The increase was the result of thermal drift caused by unwanted temperature variation of the UV LED and the filters, resulting in a zero uncertainty estimated at -560 ppm &#x00B0;C-1 and 100 ppm &#x00B0;C-1 respectively.

Non-Dispersive Ultra-Violet Spectroscopic Detection of Formaldehyde Gas for Indoor Environments