In situ monitoring of traffic-generated nitrogen dioxide (NO2) emissions using long-path absorption spectroscopy is reported. High-sensitivity detection of NO2 is achieved by employing two-tone frequency-modulation spectroscopy at a visible absorption band using a tunable high-power diode laser operated around 635 nm. A real-time absorption spectrometer is accomplished by repetitively applying a rectangular current pulse to the diode-laser operating current, allowing detection of isolated NO2 absorption lines. A detection limit of 10 μg/m3 for NO2 at atmospheric pressure using a 160 m absorption path is demonstrated. Continuous monitoring of NO2 over a road intersection at peak traffic is performed.
© 2005 Optical Society of America
Original Manuscript: November 2, 2004
Revised Manuscript: March 18, 2005
Manuscript Accepted: April 8, 2005
Published: August 20, 2005
Gabriel Somesfalean, Janis Alnis, Ulf Gustafsson, Hans Edner, and Sune Svanberg, "Long-path monitoring of NO2 with a 635 nm diode laser using frequency-modulation spectroscopy," Appl. Opt. 44, 5148-5151 (2005)