Ch3ooh c2h4 c2h2 c3h6 c6h5oh cs2 hcn

and nh3 produced in fires, in addition to co, c02, and ch4. Indeed, such FTIR studies permitted the first identification of 2-hydroxyethanal (hoch2cho) in smoke from fires (Yokelson et al., 1997a). Although such compounds could be detected and measured using chromatographic methods (see later), losses during sampling would likely be problematical, unlike open-pass FTIR, where the measurement can be made without direct sampling.

(3) Tunable diode laser spectroscopy (TDLS) A second technique based on infrared absorption spectrometry is tunable diode laser spectrometry, TDLS. The practice and application of TDLS in atmospheric measurements have been reviewed by Schiff et al. (1994a, 1994b) and Brassington (1995) and in the symposium proceedings edited by Grisar et al. (1992). As in the case of FTIR, this technique relies on measuring the absorbance at specific wavelengths due to the absorption of IR radiation by various pollutants. However, rather than using a continuous-wavelength light source and scanning the entire infrared spectrum, tunable diode laser spectroscopy employs a laser light source of very narrow linewidth that is tunable over a smaller (e.g., 100-200 cm-1) wavelength range.

TABLE 11.2 Detection Limits for Some Trace Gases in Air by FTIR," TDLSb, and Matrix Isolation IR'

Gas

FTIR detection wavenumber (cm"')

FTIR detection limit' (ppb at L = 1 km)

TDLS detection wavenumber (cm"')

TDLS detection limit1' (ppb at L = ISO m)

Matrix isolation detection limit'' (ppb)

so2

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