Laboratory, ground-based, and airborne tunable diode laser systems: performance characteristics and applications in atmospheric studies

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

“…[7] The aircraft TDLAS reported presently was initially assembled in 1999, and is the latest of four generations of TDLAS instruments developed at NCAR for CH 2 O measurement [Fried et al, 1997b[Fried et al, , 1998. While its immediate predecessor (1996 -1998) was also operated on aircraft, the instrument reported here incorporates many changes related to instrument temperature, pressure, and mechanical stability that have resulted in substantial performance improvements.…”

“…[9] Extensive laboratory studies have found that only methanol (CH 3 OH) interferes with the CH 2 O absorption feature employed [Fried et al, 1998Richter, 2001]. At equal methanol and CH 2 O concentrations this interference is +3.8%.…”

“…Ideally, fringes can be measured and reduced by replacing the sample gas in the absorption cell with air scrubbed of the target species (''zero air''), and subtracting the resulting background information from the ambient signal. Zero air based background subtraction techniques have improved instrument precisions by a factor of 3 -5 relative to unsubtracted operation of the same instrument [Fried et al, 1998]. For optimal TDLAS sensitivity, drifts in the optical system, including the laser source itself, must be minimized so that the optical background is stable over the period used to acquire both the ambient and background information (about 100 s for the system reported here).…”

Field intercomparison of a novel optical sensor for formaldehyde quantification

“…This line is free from interference of other transitions as mentioned above and shows a weak satellite transition at 2831.6987 cm −1 [Fried et al, 1998]. This smaller peak provides additional information that can be used to improve precision and accuracy of HCHO concentration measurements.…”

“…However, these techniques are limited by the required time integration of sample collection, which does not describe the rapid fluctuations in HCHO concentrations. The scale of these fluctuations is important as HCHO is an intermediate in the photooxidation of hydrocarbons that undergoes rapid photolysis to produce HOx radicals [Fried et al, 1998]. Despite the advantages of HCHO derivatization such as simplicity and relatively low cost, spectroscopic techniques provide a reliable and reproducible means of time-resolved collection of atmospheric HCHO concentrations [Vairavamurthy et al, 1992;Fried et al, 1998].…”