Development of a Detector for Trace Amount of Nitrogen Dioxide using Light Emitting Diode

Abstract

A setup based on Differential Optical Absorption Spectroscopy method is developed to detect trace amount of NO2 gas. A labview program is coded to control and collect the data and a Mathematica code is written to read and analyze the data. The components of the setup are a commercial white LED used as the light source, a 15-cm gas cell, a high resolution monochromator Horriba SPEX500M, coupled to a 3000-pixel CCD line camera Thorlab LC1-USB CCD. Two NO2 gas concentrations, 206 ppm and 2.6 ppm, are used to check the performance of the setup and the measurements are found to agree very well with the quoted concentrations by the gas cylinder supplier. The deviation of the measurements from the quoted values for the case of the 206 ppm is less than 0.4 % while for the case of the 2.6 ppm is less than 8%. The detection limit is estimated to be ~ 1.2 ppm. This limit is equivalent to ~ 0.6 ppb for a path length of 300 m which is much less than the 50 ppb long-term exposure safe limit to NO2 gas.