Measurement of atmospheric formaldehyde profiles with a laser-induced fluorescence lidar

Guangkun Li; Jie Lei; Coorg Prasad

doi:10.1117/12.918422

21 May 2012 Measurement of atmospheric formaldehyde profiles with a laser-induced fluorescence lidar

Guangkun Li, Jie Lei, Coorg Prasad

Proceedings Volume 8379, Laser Radar Technology and Applications XVII; 83790I (2012) https://doi.org/10.1117/12.918422
Event: SPIE Defense, Security, and Sensing, 2012, Baltimore, Maryland, United States

Abstract

Formaldehyde is a trace species that plays a key role in atmospheric chemistry. It is an important indicator of nonmethane volatile organic compound emissions. Also, it is a key reactive intermediate formed during the photochemical oxidation in the troposphere. Because the lifetime of formaldehyde in the atmosphere is fairly short (several hours), its presence signals hydrocarbon emission areas. The importance of measuring formaldehyde concentrations has been recognized by the National Academy's Decadal Survey and two of NASA's forthcoming missions the GEO-CAPE and GACM target its measurement. There are several techniques some of which are highly sensitive (detection limit ~ 50 parts-per-trillion) for in-situ measurement of formaldehyde and many reported atmospheric measurements. However there appear to be no reported standoff lidar techniques for range resolved measurements of atmospheric formaldehyde profiles. In this paper, we describe a formaldehyde lidar profiler based on differential laser induced fluorescence technique. The UV absorption band in the 352 - 357nm is well suited for laser excitation with frequency tripled Neodymium lasers and measuring the strong fluorescence in the 390 - 500nm region. Preliminary nighttime measurements of formaldehyde were demonstrated with a lidar using a commercial Nd:YAG laser (354.7 nm) with a rather large linewidth (~.02 nm). The measured sensitivity was ~1 ppb at 1 km with 100 meters range resolution even with this non-optimized system. In this paper we describe our approach for increasing the sensitivity by many orders and for daytime operation by improving the laser parameters (power and linewidth) and optimizing the receiver.

Citation Download Citation

Guangkun Li, Jie Lei, and Coorg Prasad "Measurement of atmospheric formaldehyde profiles with a laser-induced fluorescence lidar", Proc. SPIE 8379, Laser Radar Technology and Applications XVII, 83790I (21 May 2012); https://doi.org/10.1117/12.918422

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