Laser-induced fluorescence detection of atmospheric NO2 with a commercial diode laser and a supersonic expansion.

Routine observations of atmospheric NO2 at concentrations ranging from 0.1 to 100 parts per billion are needed for air quality monitoring and for the evaluation of photochemical models. We have designed, constructed, and field tested a relatively inexpensive and specific NO2 sensor using laser-induced fluorescence. The instrument combines a commercial cw external-cavity tunable diode laser (640 nm) and a continuous supersonic expansion. The total package is completely automated, has a modest size of 0.5 m3 and 118 kg, and could be manufactured at competitive price, with the current generation of instruments. The sensitivity of the instrument is 145 part per trillion by volume min(-1) (signal-to-noise ratio of 2), which is more than adequate for monitoring purposes.