Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS) Coupled with an Interferometer for On-Band and Off-Band Detection of Glyoxal

TL;DR

This study compares two broadband cavity-enhanced absorption spectroscopy methods for detecting atmospheric trace gases like glyoxal, methylglyoxal, and NO2, highlighting their detection limits and practical advantages.

Contribution

It introduces and evaluates two different detection techniques for trace gas analysis, providing insights into their relative sensitivities and operational considerations.

Findings

Spectrograph and CCD detection achieved ppt-level sensitivity.

Interferometer and PMT detection had higher detection limits.

Methylglyoxal detection was challenging with the interferometer method.

Abstract

Glyoxal CHOCHO is a trace gas in the atmosphere, often used as an indicator of biogenic emissions. It is frequently compared to formaldehyde concentrations, which serve as indicators of anthropogenic emissions, to gain insights into the characteristics of the environmental source. This study employed broadband cavity-enhanced absorption spectroscopy to detect gaseous CHOCHO, methylglyoxal, and $\mathrm{NO_2}$. Two different detection methods are compared. Spectrograph and CCD Detection: This approach involves coupling the system to a spectrograph with a charge-coupled device (CCD) detector. It achieved a 1 min 1-$\sigma$ detection limit of $2.5 \times 10^8$ molecules/cm$^3$, or 10 parts per trillion (ppt). Methylglyoxal and $\mathrm{NO_2}$ achieved 1 min 1-$\sigma$ detection limits of 34 ppt and 22 ppt, respectively. Interferometer and PMT Detection: In this method, an interferometer is used in conjunction with a photomultiplier tube (PMT) detector. It resulted in a 2 min 1-$\sigma$ detection limit of $1.5 \times 10^{10}$ molecules/cm$^3$, or 600 ppt. The $\mathrm{NO_2}$ 2 min 1-$\sigma$ detection limit was determined to be 900 ppt. Concentrations of methylglyoxal were difficult to determine using this method, as they appeared to be below the detection limit of the instrument. This study discusses the advantages and limitations of each of these detection methods.