A new airborne laser-induced fluorescence instrument for in situ detection of formaldehyde throughout the troposphere and lower stratosphere
- 1Atmospheric Chemistry and Dynamics Lab, NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 2Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
- 3Goddard Earth Sciences Technology and Research, University of Maryland Baltimore County, Baltimore, MD, USA
- 4Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA
- *now at: Universidad San Francisco de Quito, Instituto de Investigaciones Atmosféricas, Colegio de Ciencias e Ingeniería, Diego de Robles y Vía Interoceánica, Quito, Ecuador
Abstract. The NASA In Situ Airborne Formaldehyde (ISAF) instrument is a high-performance laser-based detector for gas-phase formaldehyde (HCHO). ISAF uses rotational-state specific laser excitation at 353 nm for laser-induced fluorescence (LIF) detection of HCHO. A number of features make ISAF ideal for airborne deployment, including (1) a compact, low-maintenance fiber laser, (2) a single-pass design for stable signal response, (3) a straightforward inlet design, and (4) a stand-alone data acquisition system. A full description of the instrument design is given, along with detailed performance characteristics. The accuracy of reported mixing ratios is ±10% based on calibration against IR and UV absorption of a primary HCHO standard. Precision at 1 Hz is typically better than 20% above 100 pptv, with uncertainty in the signal background contributing most to variability at low mixing ratios. The 1 Hz detection limit for a signal / noise ratio of 2 is 36 pptv for 10 mW of laser power, and the e fold time response at typical sample flow rates is 0.19 s. ISAF has already flown on several field missions and platforms with excellent results.