A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide.

Silvia Viciani,Alessio Montori,Francesco D’Amato,Antonio Chiarugi

doi:10.3390/s18072380

Abstract

Trace gas concentration measurements in the stratosphere and troposphere are critically required as inputs to constrain climate models. For this purpose, measurement campaigns on stratospheric aircraft and balloons are being carried out all over the world, each one involving sensors which are tailored for the specific gas and environmental conditions. This paper describes an automated, portable, mid-infrared quantum cascade laser spectrometer, for in situ carbon monoxide mixing ratio measurements in the stratosphere and troposphere. The instrument was designed to be versatile, suitable for easy installation on different platforms and capable of operating completely unattended, without the presence of an operator, not only during one flight but for the whole period of a campaign. The spectrometer features a small size (80 × 25 × 41 cm), light weight (23 kg) and low power consumption (85 W typical), without being pressurized and without the need of calibration on the ground or during in-flight operation. The device was tested in the laboratory and in-field during a research campaign carried out in Nepal in summer 2017, onboard the stratospheric aircraft M55 Geophysica. The instrument worked extremely well, without external maintenance during all flights, proving an in-flight sensitivity of 1–2 ppbV with a time resolution of 1 s.

Highlights

A detailed knowledge of composition and evolution of the atmosphere is fundamental for the inputs to any predictive climate model
Its mixing ratio decreases of about one order of magnitude when moving from the troposphere, where its lifetime does not exceed a couple of months, to the stratosphere, where it can reside up to several months at lower concentrations
COLD2 is equipped with a multipass cell whose rear mirror can vibrate along the optical axis by means of a piezoelectric transducer (PZT)

Summary

Introduction

A detailed knowledge of composition and evolution of the atmosphere is fundamental for the inputs to any predictive climate model. The chemistry of atmospheric compounds, their transportation around the world and their evolution under climate changes provide essential information for any climatological study and forecast. Some gases play the role of tracers, as they exhibit particular features in terms of sources, reactivity, concentration and lifetime. Carbon Monoxide (CO) is an ideal tracer of atmospheric transport for several reasons. Its mixing ratio decreases of about one order of magnitude when moving from the troposphere, where its lifetime does not exceed a couple of months, to the stratosphere, where it can reside up to several months at lower concentrations. CO can be used as tracer of air transport across the tropopause, witnessed by too low mixing ratio in the troposphere or too high mixing ratio in the stratosphere, as might occur during strong convective activity [1]. The analysis of the CO-ozone correlation, which is negative in the stratosphere and dependent on season and latitude in Sensors 2018, 18, 2380; doi:10.3390/s18072380 www.mdpi.com/journal/sensors

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