Development of a Differential Optical Absorption Spectroscopy System Using High
Luminance LED for Measurement of NO₂

Abstract

A differential optical absorption spectroscopy (DOAS) system for measurement of atmospheric NO₂ was developed. The system uses a battery-operated, high luminance LED and a fiber-coupled spectrometer, and is portable. Laboratory experiments using a gas cell of length 0.22 m with varying NO₂ concentrations were performed to evaluate the sensitivity of the DOAS system. The DOAS measurement results are in agreement with NO₂ concentrations obtained simultaneously by a FT-IR (Fourier Transform Infrared) system for NO₂ concentrations down to 20 ppm. Experiments with an optical path length of 93 m were also performed, and NO₂ concentrations down to 0.20 ppm were measured. Since measurement of atmospheric NO₂, which is in the order of several tens of ppb, requires optical path lengths of several hundred m, system improvements to improve the signal detection are necessary.