Tunable diode laser absorption spectrometer for ground‐based measurements of formaldehyde

Intercomparison of six ambient [CH2O] measurement techniques

“…Lower concentrations in the 0.2-2 ppbv range were generated by the permeation calibration system (experiments l a-Sb, Table 1). These approaches have been discussed in detail by Fried et al [1997] and will thus be described only briefly here.…”

“…In this procedure the laser modulation was turned off, and the incident and transmitted intensities were measured as the laser was repetitively scanned across the CH20 absorption feature at 2831.6417 cm -• (see Figure 2). This absorption line, which was employed for all TDLAS measurements throughout this study, is clear of any known spectral interferences [Fried et al, 1997]. The above intensities were used together with measurements of sample pressure (= 30 torr), cell temperature (26.8øC), path length (100 m), and known spectroscopic parameters (absorption coefficient, Doppler, and pressure-broadening coefficients) in a nonlinear least squares fitting routine to determine both the absorption at the line center and the integrated absorption across the line.…”

“…It was used to deliver known CH20 concentrations in the 3-12 ppbv range to the TDLAS for frequent calibration purposes [see Fried et al, 1997]. The HLD-calibrated output was determined using the temperature-dependent Henry's law coefficients of Dong and Dasgupta [1986], along with measurements of pressure, temperature, flow, and solution concentrations.…”

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.…”

“…Where applicable, the present system will be contrasted with previous systems, to illuminate factors that have produced this improved performance. In an effort to provide a comprehensive assessment of instrument performance, some supporting material that was published previously is summarized here [Fried et al, 1997a[Fried et al, , 1997b[Fried et al, , 2003aWert et al, 1996Wert et al, , 2002Wert et al, , 2003]. …”