CAFE: a new, improved nonresonant laser-induced fluorescence instrument for airborne in situ measurement of formaldehyde

Abstract. NASA Compact Airborne Formaldehyde Experiment (CAFE) is a nonresonant laser-induced fluorescence instrument for airborne in situ measurement of formaldehyde (HCHO). The instrument is described here with highlighted improvements from the predecessor instrument, COmpact Formaldehyde FluorescencE Experiment (COFFEE). CAFE uses a 480 mW, 80 kHz laser at 355 nm to excite HCHO and detects the resulting fluorescence in the 420–550 nm range. The fluorescence is acquired at 5 ns resolution for 500 ns and the unique time profile of the HCHO fluorescence provides measurement selectivity. CAFE achieves a 1σ precision of 160 pptv (1 s) and 90 pptv (10 s) for [HCHO]  =  0 pptv. The accuracy of CAFE, using its curve-fitting data processing, is estimated as ±20  % of [HCHO]  +  100 pptv. CAFE has successfully flown on multiple aircraft platforms and is particularly well-suited to high-altitude research aircraft or small air quality research aircraft where high sensitivity is required but operator interaction and instrument payload is limited.