A new airborne laser-induced fluorescence instrument for in situ detection of formaldehyde throughout the troposphere and lower stratosphere

摘要

The NASA In Situ Airborne Formaldehyde (ISAF) instrument is ahigh-performance laser-based detector for gas-phase formaldehyde (HCHO). ISAFuses rotational-state specific laser excitation at 353 nm for laser-inducedfluorescence (LIF) detection of HCHO. A number of features make ISAF idealfor airborne deployment, including (1) a compact, low-maintenance fiberlaser, (2) a single-pass design for stable signal response, (3) astraightforward inlet design, and (4) a stand-alone data acquisition system. Afull description of the instrument design is given, along with detailedperformance characteristics. The accuracy of reported mixing ratios is±10% based on calibration against IR and UV absorption of a primaryHCHO standard. Precision at 1 Hz is typically better than 20% above100 pptv, with uncertainty in the signal background contributing most tovariability at low mixing ratios. The 1 Hz detection limit for asignal / noise ratio of 2 is 36 pptv for 10 mW of laser power, and the fold time response at typical sample flow rates is 0.19 s. ISAF hasalready flown on several field missions and platforms with excellent results.