Measurement Techniques Analytical Methods

Measurements of atmospheric CO are conducted using a variety of techniques. Solar spectra recorded at 4.7 (im are used to derive total column abundances and column-averaged mixing ratios.12'13 Nondispersive infrared radiometry (NDIR)14'15 and tunable diode laser spectroscopy (TDLS)16 also make use of CO absorption at 4.7 (^m. Both techniques provide a continuous measurement of CO; however, the TDLS provides greater precision (1 ppb) and a higher measurement frequency (10 s), about a factor of 10 greater than NDIR. Gas chromatography (GC), when coupled with a number of different detectors can provide high precision and low detection limits.17^19 The most common detectors used with GC are flame ionization (with prior conversion of CO + H2 -»• CH4), electron capture, and hot mercuric oxide reduction. GC techniques can provide a high precision (1 ppb) with a discontinuous measure of CO (frequency on the order of a few minutes).20

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