ULTRASENSITIVE, VISIBLE TUNABLE DIODE-LASER DETECTION OF NO2

Recent advances in room-temperature visible diode lasers and ultrasens itive detection techniques have been exploited to create a highly sens itive tunable diode laser absorption technique for in situ monitoring of NO2 in the lower troposphere. High sensitivity to NO2 is achieved b y probing the visible absorption band of NO2 with an AlGaInP diode las er at 640 or 670 nm combined with a balanced ratiometric electronic de tection technique. We have demonstrated a sensitivity of 3.5 x 10(10) cm(-3) for neat NO2 in a l-m path at 640 nm and have estimated a sensi tivity for ambient operation of 5 ppbv m (10 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. (C) 1996 Optical Soci ety of America