Long-path monitoring of NO_(2) with a 635 nm diode laser using frequency-modulation spectroscopy

摘要

In situ monitoring of traffic-generated nitrogen dioxide (NO_(2)) emissions using long-path absorption spectroscopy is reported. High-sensitivity detection of NO_(2) 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 NO_(2) absorption lines. A detection limit of 10 (mu)g/m~(3) for NO_(2) at atmospheric pressure using a 160 m absorption path is demonstrated. Continuous monitoring of NO_(2) over a road intersection at peak traffic is performed.