Long-path absorption measurements

Long-path absorption measurements for [HO ] have been primarily developed by researchers in Germany (122,123,124,125). This approach measures the uv absorption by HO over a pathlength up to several kilometers. The result is an HO concentration spatially averaged over the... 

Dorn, H.-P., R. Neuroth, and A. Hofzumahaus, Investigation of OH Absorption Cross Sections of Rotational Transitions in the A2 L +, r = 0 - X2II, c" = 0 Band under Atmospheric Conditions Implications for Tropospheric Long-Path Absorption Measurements, J. Geophys. Res., 100, 7397-7409 (1995b). 

Johnston, P. V. and R. L. McKenzie (1984). Long path absorption measurements of tropospheric N02 in rural New Zealand. Geophys. Res. Lett. 11, 69-72. 

Fig. 10.17. Long-path absorption measurement of atmospheric pollutants 320...

Dorn, H.-P., U. Brandenburger, T. Brauers, and M. Hausmann, A New In-Situ Laser Long-Path Absorption Instrument for the Measurement of Tropospheric OH Radicals, J. Atmos. Sci., 52, 3373-3380 (1995a). 

Mount, G. H., and J. W. Harder, The Measurement of Tropospheric Trace Gases at Fritz Peak Observatory, Colorado, by Long-Path Absorption OH and Ancillary Gases, . /. Atmos. Sci., 52, 3342-3353 (1995). 

In addition, CH3 and OH radical concentration profiles are depicted in Fig. 9 which were measured using the in situ long path absorption technique described in Ref. 61(a). The OH radical profile was determined from... 

A new in situ long-path absorption instmment for the measurement of tropospheric OH radicals. J. Atmos. Sci. 52, 3373-3380. 

Hofzumahaus, A., Dom, H.-P., Callies, J., Platt, U., and Ehhalt, D., Tropospheric OH concentration measurements by laser long-path absorption spectroscopy. Atmos. Environ. 25A, 2017 (1992). 

New high resolution (0.01 nm) measurements of the absorption cross-sections of NO2 were performed in the 300-500 nm range at 293, 240 and 220 K using a coolable 5m long path absorption cell (Malicet). Experiments were carried out at very low NO2 pressures in order to reduce absorption contributions of the dimer, N2O4. A definite temperature effect (up to 6 %) was observed in the structured region of the spectrum. 

As the cold-vapor mercury sample is already in the atomic state, there is no need of an atomizer, per se. The vapor, transferred directly from the cell or desorbed as a plug from a heated amalgamation trap, is commonly swept into a moderately heated (resistance wound heating to 200°C) 10 cm quartz T-tube located within the optical beam of a conventional AA spectrometer. Attenuation of an intense electrodeless discharge lamp line source at 253.7nm is used as a measure of the absorption. Alternatively, dedicated continuum source AA-based spectrometers fitted with long path absorption cells (30 cm) are frequently used to increase sensitivity and detection limit. 

The principle of long-path absorption techniques is illustrated in Fig. 10.17. A laser beam is transmitted continuously into the atmosphere against a corner-cube retro-reflector (Fig. 6.21) that is placed at a distance of up to 10 km. The reflected beam is received by an optical telescope that is placed at the site of the laser and is directed towards the retro-reflector. The received light intensity is measured photo-electrically as a function of the laser wavelength. The absorption spectrum of the atmosphere between the laser and the retro-reflector is then recorded and the mean concentrations Nj of pollutant molecules can be determined using the Beer-Lambert relation... 

In order to measure the concentration of gaseous pollutants with lidar techniques, resonance absorption can be used in a similar way to the long-path-absorption method that was described above. However, in the lidar technique no retro-reflector is required and the scattering from particles is... 

In a variant of the long-path absorption technique, radiation from a diode laser or a light-emitting diode is transmitted fibre-optically to remotely located multi-pass absorption cells (Sects. 6.5.6, 9.2.1) and the partially absorbed beam is sent back to the measurement system also using fibre-optics. Using such a system, wliich operates at short IR wavelengths (1 to 2 pm) at which... 

A. Minato, T. Kobayashi, N. Sugimoto Laser long-path absorption technique for measuring methane using gas correlation method. J. Appl. Phys. 

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