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Proceedings Paper

High-sensitivity remote detection of atmospheric pollutants and greenhouse gases at low ppm levels using near-infrared tunable diode lasers
Author(s): Anirban Roy; Abhishek Upadhyay; Arup Lal Chakraborty
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Paper Abstract

The concentration of atmospheric pollutants and greenhouse gases needs to be precisely monitored for sustainable industrial development and to predict the climate shifts caused by global warming. Such measurements are made on a continuous basis in ecologically sensitive and urban areas in the advanced countries. Tunable diode laser spectroscopy (TDLS) is the most versatile non-destructive technology currently available for remote measurements of multiple gases with very high selectivity (low cross-sensitivity), very high sensitivity (on the order of ppm and ppb) and under hazardous conditions. We demonstrate absolute measurements of acetylene, methane and carbon dioxide using a fielddeployable fully automated TDLS system that uses calibration-free 2f wavelength modulation spectroscopy (2f WMS) techniques with sensitivities of low ppm levels. A 40 mW, 1531.52 nm distributed feedback (DFB) diode laser, a 10 mW, 1650 nm DFB laser and a 1 mW, 2004 nm vertical cavity surface emitting laser (VCSEL) are used in the experiments to probe the P9 transition of acetylene, R4 transition of methane and R16 transition of carbon dioxide respectively. Data acquisition and on-board analysis comprises a Raspberry Pi-based embedded system that is controllable over a wireless connection. Gas concentration and pressure are simultaneously extracted by fitting the experimental signals to 2f WMS signals simulated using spectroscopic parameters obtained from the HITRAN database. The lowest detected concentration is 11 ppm for acetylene, 275 ppm for methane and 285 ppm for carbon dioxide using a 28 cm long single-pass gas cell.

Paper Details

Date Published: 5 May 2016
PDF: 7 pages
Proc. SPIE 9876, Remote Sensing of the Atmosphere, Clouds, and Precipitation VI, 98761W (5 May 2016); doi: 10.1117/12.2222785
Show Author Affiliations
Anirban Roy, Indian Institute of Technology, Gandhinagar (India)
Abhishek Upadhyay, Indian Institute of Technology, Gandhinagar (India)
Arup Lal Chakraborty, Indian Institute of Technology, Gandhinagar (India)

Published in SPIE Proceedings Vol. 9876:
Remote Sensing of the Atmosphere, Clouds, and Precipitation VI
Eastwood Im; Raj Kumar; Song Yang, Editor(s)

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