Abstract

In times of steadily increasing air pollution especially in urban areas, the monitoring of nitrogen dioxide (NO2) has gained in importance and with it the search for compact, low-cost sensors. We present a novel approach to measure NO2 in sub-ppm concentrations with a photoacoustic sensor utilizing a T-shaped resonance cell. An inexpensive single LED with a peak wavelength of 410 nm was used as radiation source and the acoustic detection was done with a commercial MEMS microphone. For optimal coupling of the divergent LED light into the cell, the T-shaped resonator was developed and fabricated with rapid prototyping methods. The resonator shows a acoustic Q-factor >10 while having nearly no zero gas signal.

Highlights

  • NO2 is a highly toxic gas, which originates mostly from combustion processes in power plants or motor vehicles

  • The resonant photoacoustic sensor we present reaches a high sensitivity with the usage of a low cost LED and a commercial MEMS microphone

  • Due to the high amplification, the second mode was chosen as frequency range for the gas measurement

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Summary

Introduction

NO2 is a highly toxic gas, which originates mostly from combustion processes in power plants or motor vehicles. Because NO2 can already be hazardous in concentrations of only a few parts per million (ppm), it is necessary to monitor the NO2 concentration in the environment whenever these processes take place in confined spaces, e.g., underground parking garages or road tunnels [1]. NO2 is measured by electrochemical sensors or large absorption photometers. Electrochemical sensors show a high sensitivity to NO2 and they are small and cost effective, but require a frequent replacement, due to their limited lifetime. IR-absorption photometers on the other hand need an absorption path of several meters to gain a sufficient sensitivity, which makes them costly and very large. The resonant photoacoustic sensor we present reaches a high sensitivity with the usage of a low cost LED and a commercial MEMS microphone. For an efficient coupling of the light into the cell, we present a Tshaped resonator design with a resonance frequency in the kHz range

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