A two-photon laser-induced fluorescence field instrument for ground-based and airborne measurements of atmospheric NO.

This paper reports on a new two-photon laser-induced fluorescence (TP-LIF) sensor capable of making routine measurements at the few parts per trillion volume level. This direct spectroscopic detection method has been demonstrated to be a reliable instrument while performing both on the ground and in the air. As currently designed it is unique in being 'signal' rather than 'signal-to-noise' limited. The latter characteristic enables the TP-LIF sensor to make atmospheric measurements of NO under environmental conditions that might normally be considered unsuitable for a laser technique. These include clouds, rain, and, in general, high-atmospheric-aerosol loading conditions. Of special interest is the insensitivity of the TP-LIF NO instrument to changes in pressure while operating in the troposophere. This characteristic has enabled this sensor to be used to record real-time altitude profiles of NO. Future improvements should make possible two measurement opportunities: 1) NO flux measurements via the airborne eddy-correlation method and 2) nitrogen isotopic distribution measurements (eg N¹⁵O¹⁶ versus N¹⁴O¹⁶) as a means of identifying specific NO_x sources.-Authors