Implementation of the DOAS Method for Measuring Concentrations of Chlorine and Bromine Oxide Molecules in the Atmosphere
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IMPLEMENTATION OF THE DOAS METHOD FOR MEASURING CONCENTRATIONS OF CHLORINE AND BROMINE OXIDE MOLECULES IN THE ATMOSPHERE IN THE UV REGION OF THE SPECTRUM P. P. Geiko1,2 and S. S. Smirnov1
UDC 551.508.953
The method of differential optical absorption spectroscopy is an effective tool for long (several hundred meters) path measurements of the integral concentration of atmospheric gases and pollutants. A portable lowenergy gas analyzer instrument for remote path measurements of gaseous pollution in the atmosphere has been proposed. The gas analyzer comprised a set of ultraviolet LEDs emitting in the UV region of the spectrum, a multi-core optical fiber, a transceiving telescope, a spectrometer, and a data processing system. The paper describes the technique and gives some results of field measurements of concentrations of a number of gaseous pollutants in the atmosphere. Keywords: differential optical absorption spectroscopy, UV light emitting diodes, atmosphere, gaseous pollution.
INTRODUCTION Over the last few years, the classical differential absorption method has been significantly improved so that it became possible to use a greater number of spectral components instead of two on- and off-line components for the detection and evaluation of gaseous pollutant concentrations. The spectrum is processed by subtraction of the path absorption spectrum and subsequent comparison of the difference spectrum with the individual absorption spectra of the examined gases based on statistical tests. Such approach was called the method of differential optical absorption spectroscopy (DOAS). It allows a number of gases to be identified simultaneously and is promising for long-path measurements of the integral concentration of atmospheric and polluting gases [1]. This method permits measurements of concentrations of a large number of gases in real time. DOAS gas analyzers can measure average concentrations on atmospheric paths up to several kilometers and allow 3D-maps of pollution to be obtained [2]. The DOAS method also has the advantages of most spectroscopic methods, including high sensitivity up to several ppt (parts per trillion). High-pressure xenon lamps that require high-voltage power supply are conventionally used as radiation sources in the gas analyzers implementing the DOAS method, which makes such gas analyzers bulky and energy-dependent [3, 4]. UV light-emitting diodes that have appeared relatively recently are potentially promising radiation sources for the gas analyzers, because they have a smooth spectrum 10–60 nm wide. The present work is devoted to investigation of the potential capabilities and the practical implementation of the DOAS method for determining the integral path concentration of halogen oxide molecules in the outdoor atmosphere in the UV region of the spectrum. An interest in remote control of the halogen oxide content in the atmosphere is stimulated by various applications, in particular, in chemistry of power-intensive compounds, investigation of volcanic eruptions, etc.
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National Research
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