Portable Fiber-Optic Real-Time Nitrogen Dioxide Monitor

Using Combined Wavelength and Frequency Modulation Spectroscopy coupled with fiber coupled near infrared diode laser, nitrogen dioxide can be detected via its near infrared absorption band. Detection sensitivity in the parts-per-billion level can be achieved. The technique offers 5 decades of linear dynamic range with a response time less than 1 second. Continuous time weight average monitoring is also possible. This technique has the advantage of high chemical selectivity, high sensitivity and non-intrusive nature of detection. Absorbance as low as a few parts in 10-8 can be detected. The use of diode laser and its pure electronic modulation-demodulation scheme permits a compact and portable instrument design. Hence, make possible the lightweight nitrogen dioxide detector. It also excludes some problems of existing detection technology which include: chemical reaction interferences, poor chemical selectivity, slow response, low sensitivity, bulky instrumentation, over concentration sample cell poisoning and optical window contamination induced problems.