Ultrasensitive, visible tunable diode laser detection of NO(2)

Recent advances in room-temperature visible diode lasers and ultrasensitive detection techniques have been exploited to create a highly sensitive tunable diode laser absorption technique for in situ monitoring of NO(2) in the lower troposphere. High sensitivity to NO(2) is achieved by probing the visible absorption band of NO(2) with an AlGalnP diode laser at 640 or 670 nm combined with a balanced ratiometric electronic detection technique. We have demonstrated a sensitivity of 3.5 × 10(10) cm(-3) for neat NO(2) in a 1-m path at 640 nm and have estimated a sensitivity for ambient operation of 5 ppbv m (l0 ppbv m at 670 nm), where ppbvm is parts in 10(9) by volume per meter of absorption path length, from measured pressure-broadening coefficients.