Abstract
Abstract. A new in situ instrument for gas-phase formaldehyde (HCHO), COmpact Formaldehyde FluorescencE Experiment (COFFEE), is presented. COFFEE utilizes non-resonant laser-induced fluorescence (NR-LIF) to measure HCHO, with 300 mW of 40 kHz 355 nm laser output exciting multiple HCHO absorption features. The resulting HCHO fluorescence is collected at 5 ns resolution, and the fluorescence time profile is fit to yield the ambient HCHO mixing ratio. Typical 1σ precision at ∼ 0 pptv HCHO is 150 pptv for 1 s data. The compact instrument was designed to operate with minimal in-flight operator interaction and infrequent maintenance (1–2 times per year). COFFEE fits in the wing pod of the Alpha Jet stationed at the NASA Ames Research Center and has successfully collected HCHO data on 27 flights through 2017 March. The frequent flights, combined with a potentially long-term data set, makes the Alpha Jet a promising platform for validation of satellite-based column HCHO.
Highlights
Formaldehyde (HCHO) is an abundant, photochemically influential trace species in the Earth’s atmosphere
Primary sources of HCHO include biomass burning (Akagi et al, 2011; Andreae and Merlet, 2001) and fossil fuel combustion (Anderson et al, 1996; Luecken et al, 2012; Olaguer et al, 2009), but these are dwarfed by secondary production from the photochemical oxidation of volatile organic compounds (VOCs)
We present a new approach to the measurement of HCHO by non-resonant laserinduced fluorescence (NR-LIF), using a fixed-wavelength UV industrial laser at 355 nm to excite multiple HCHO absorption features simultaneously
Summary
Formaldehyde (HCHO) is an abundant, photochemically influential trace species in the Earth’s atmosphere. LIF measurements of HCHO have used a wavelength-tunable excitation laser to dither on and off the HCHO absorption feature, using the difference in signal to calculate the HCHO mixing ratio. We present a new approach to the measurement of HCHO by non-resonant laserinduced fluorescence (NR-LIF), using a fixed-wavelength UV industrial laser at 355 nm to excite multiple HCHO absorption features simultaneously. The new NR-LIF HCHO instrument, COmpact Formaldehyde FluorescencE Experiment (COFFEE), was designed to join the payload of the Alpha Jet Atmospheric eXperiment (AJAX) out of the NASA Ames Research Center in Mountain View, CA. Other LIF-based instruments for atmospheric HCHO (Cazorla et al, 2015; Hottle et al, 2009) collect fluorescence using a long-pass filter to exclude scatter and achieve measurement selectivity by alternately tuning the narrow-bandwidth laser on and off an HCHO absorption feature. The laser side of the TECs is controlled to 303 K, and the other side of the TECs are in thermal contact with the optical plate and heat sinks mounted to the underside of the optical plate
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