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Chinese researchers develop LED-based sensor for detecting nitrogen dioxide
Article Type: Mini features From: Sensor Review, Volume 29, Issue 2
Nitrogen dioxide (NO2) is one of the main air pollutants and is monitored routinely in stack emissions and in the ambient environment. The techniques used, such as chemiluminescence and laser-based approaches are complex and costly but researchers from the Department of Physics at the Chinese Harbin Institute of Technology have developed a far simpler means of detecting this gas. Based on blue LEDs, the technique exploits the Beer-Lambers absorption principle, whereby the intensity of light at a particular wavelength is reduced through absorption by the target gas. To exploit this technique a lens with a focal length of 100 mm was used to collect light emitted by a broadband 100 mW LED, operating from 456 to 484 nm. This wavelength range is particularly well suited to detecting NO2, since this gas exhibits strong absorption at 465 nm and has sufficiently well resolved spectral features to reduce interference from other species.
The light was transmitted through a 50 cm long gas cell containing NO2 and the light leaving the cell was focused by a collimating lens and collected and analysed by a spectrometer consisting of a monochromator and a 2048-element CCD array detector. In this way, real-time measurements of NO2 concentrations were made at room temperature and atmospheric pressure, yielding a limit of detection ~3 ppm for an integration time of 2seconds. Aimed at measuring NO2 emissions from coal-fired combustion plant, a prototype instrument has been developed (Figure 2) and the group has recently set up a company to commercialise the technology. They are now investigating how to detect other pollutants such as airborne mercury and arsenic and means of further reducing the cost of the instrument.
This research was reported in Applied Optics, Vol. 47 No. 29, pp. 5337-40, in a paper entitled “Nitrogen dioxide monitoring using a blue LED”.