Formaldehyde is a volatile organic compound that exists as a gas at room temperature. It is hazardous to human health causing irritation of the eyes, nose and throat, headaches, limited pulmonary function and is a potential human carcinogen. Sources include incomplete combustion, numerous modern building materials and vehicle fumes. Here we describe a simple method for detecting formaldehyde using low resolution non-dispersive UV absorption spectroscopy for the first time. A two channel system has been developed, making use of a strong absorption peak at 339nm and a neighbouring region of negligible absorption at 336nm as a reference. Using a modulated UV LED as a light source and narrowband filters to select the desired spectral bands, a simple detection system was constructed that was specifically targeted at formaldehyde. A minimum detectable absorbance of 4.5 × 10-5 AU was estimated (as ΔI/I0), corresponding to a limit of detection of approximately 6.6 ppm for a 195mm gas cell, with a response time of 20s. However, thermally-induced drift in the LED spectral output caused this to deteriorate over longer time periods to around 30 ppm or 2 × 10-4 AU.
We present the results of a study into the noise behaviour of an Avaspec-3648 CCD UV spectrometer for use in a
spectroscopic gas detection system. A comparison was made between a deuterium UV lamp and a range of newly
developed UV LEDs. A number of noise phenomena were identified and quantified including source fluctuation noise,
photo-response non-uniformity (PRNU), dark current noise, fixed pattern noise (FPN) and read noise. For spectral
measurements the dominant noise phenomenon was PRNU, giving a noise equivalent absorption (NEA) of 8 x 10-3 AU.
A set of noise limitation techniques is presented, which decreases the NEA to 2 x 10-3 AU.