Detection of H_2O and CO_2 with distributed feedback diode lasers: measurement of broadening coefficients and assessment of the accuracy levels for volcanic monitoring

Abstract

We reproduced the chemical-physical conditions of fumarolic emission at Phlaegrean Fields, Pozzuoli, Italy, and we measured the CO(2) and H(2)O concentrations using an absorption spectrometer based on two distributed feedback laser diodes at wavelengths of 1.578 and 1.393 microm. We discuss the accuracy levels of the different methods used. Furthermore, we measured the broadening coefficients for H(2)O (self-broadening, 28.2 +/- 0.6 MHz/Torr; CO(2) broadening, 6.0 +/- 0.4 MHz/Torr) and CO(2) (self-broadening, 3.2 +/- 0.1 MHz/Torr; H(2)O broadening, 4.0 +/- 0.1 MHz/Torr). Using the present data, we evaluated a minimum detectable variation of 9% for H(2)O and 1% for CO(2).