Tunable diode laser and difference frequency generation absorption spectrometers for highly sensitive airborne measurements of trace atmospheric constituents

Abstract

Enhancing our understanding of atmospheric processes and transformations require a suite of ever more sensitive, selective, versatile, and fast instruments that can measure trace atmospheric constituents at and below mixing ratios of 100-parts-per-trillion on airborne platforms. Instruments that can carry out such measurements are very challenging, as airborne platforms vibrate, experience accelerations, and undergo large swings in cabin temperatures and pressures. These challenges notwithstanding, scientists and engineers at the National Center for Atmospheric Research (NCAR) in collaboration with Rice University have long been employing mid-infrared absorption spectroscopy to acquire atmospheric measurements of important trace gases like formaldehyde on a variety of airborne platforms. The present paper will discuss two very recent airborne formaldehyde instruments employing tunable diode laser and difference frequency generation mid-IR laser sources. Both instruments employ second-harmonic absorption spectroscopy utilizing astigmatic multipass Herriott cells. This paper will discuss the performance of both instruments during recent airborne campaigns, focusing on the many steps necessary for minimizing the various aircraft perturbations. Prospects for the detection of other trace gases will also be presented.