Advances in hardware, system diagnostics software, and acquisition procedures for high performance airborne tunable diode laser measurements of formaldehyde

A tunable diode laser absorption spectroscopy (TDLAS) instrument was deployed onboard a DC-8 aircraft as part of the International Chemical Transport Experiment – North America (INTEX-NA) during the summer of 2004 to quantify atmospheric formaldehyde (CH₂O) concentrations. A number of improvements, both software and hardware, are discussed and include the laser tuning waveform, spectral wavelength centering, and optical stabilization. In addition, the impact of perturbations to the instrument in flight is reviewed and a number of advanced TDLASdata-acquisition and processing concepts are introduced to identify the presence of optical perturbations in flight to objectively eliminate such perturbed data, assess the validity of the fitting routine in the presence of perturbed data, provide various diagnostic measures to elucidate system behavior, and assess the efficacy of various opto-mechanical improvements implemented to reduce the magnitude of such perturbations. The concepts specific to our TDLASmeasurements of CH₂O should have broader and more universal applicability to measurement of other trace gases and possibly other methods of detection.