Airborne tunable diode laser measurements of formaldehyde

Accurate measurements of formaldehyde (CH2O) in the atmosphere are essentia l to further our understanding of various atmospheric cycles involving hydr ogen and carbon-containing species. Comparisons among independent measureme nts of this gas and between measurements and model calculations have raised numerous questions regarding the veracity of both endeavors. The present p aper describes a long-term effort by our group to develop and employ tunabl e diode laser absorption spectroscopy (TDLAS) for highly accurate measureme nts of this gas on both ground-based and aircraft platforms. A highly sensi tive and selective TDLAS system, which has successfully flown on three diff erent aircraft campaigns, will be described. Many new hardware and software features, which have been implemented, now make it possible to detect ambi ent CH2O concentrations as low as 55 parts-per-trillion employing a 20-s in tegration time. This paper will also discuss the many aspects associated wi th high accuracy and its verification, including a brief discussion of our aircraft sampling system and inlet surface effects. (C) 1999 Elsevier Scien ce B.V. All rights reserved.