Active photometry of atmospheric compositions by microwave breakdown plasma spectroscopy

Abstract

A laboratory technique of pulsed microwave breakdown plasma spectroscopy (MBS) has been developed for simultaneous, quantitative, in situ, and remote diagnostics of atmospheric compositions. This technique, based upon a concept proposed by Papadopoulos et al. [1994], enables for remote photometry of the atomic/molecular spectra emitted from the microwave breakdown plasma of the atmosphere mixed with various kinds of trace gases and air pollutants at relevant breakdown spots in open space. Two different breakdown methods, the single beam method and the dual beam intersection method, have been tested using a small test chamber, a pulsed 9.4 GHz/100 kW magnetron tube, and a high‐resolution wavelength/time resolution spectroscopy system. Major 50 lines of atomic/molecular spectra emitted from N2, O2, Cl, F, CN, and OH radical in the plasma of model/real atmosphere have been assigned and compared with the emission candidates in the stratosphere predicted by Papadopoulos et al. Very many strong emission lines including, for example, 837.6 nm (4p4D07/2 → 4s4P5/2) of Cl(I) and 777.4 nm (3p5P1,2,3 → 3s5S02) of O(I) can be observed, most of which have not been expected yet in their theoretical approach. Also, the controllability of the pulsed microwave breakdown power as well as the quantitative detection limit of trace gases has been examined both experimentally and theoretically.