H2O Collisional Broadening Coefficients at 1.37 µm and Their Temperature Dependence: A Metrology Approach

Javis A Nwaboh,Olav Werhahn,Volker Ebert

doi:10.3390/app11125341

Abstract

We report self- and air collisional broadening coefficients for the H2O line at 7299.43 cm−1 and corresponding temperature coefficients for a temperature range spanning 293–573 K. New laser spectroscopic setups specifically designed for this purpose have been developed and are described. The line parameters reported here are in good agreement with those values reported in the HITRAN 2020 database, but the uncertainties have been reduced by factors of about 4, 1.3 and 4.4 for the self-broadening coefficient, air broadening coefficient and the temperature exponent of air broadening, respectively. Further, we combined our measurement approach with metrological data quality objectives, addressing the traceability of the results to the international system of units (SI) and evaluated the uncertainties following the guide to the expression of uncertainty in measurement (GUM).

Highlights

Water vapor is the most abundant greenhouse gas and is routinely measured in atmospheric chemistry research [1,2,3]
We report self- and air collisional broadening coefficients for the H2O line at 7299.43 cm−1 and corresponding temperature coefficients for a temperature range spanning 293–573 K
We report improved and metrology-compatible collisional line data for the H2O line at 7299.43 cm−1 (000–101, 110–211) often used in atmospheric H2O measurements [3,5,6,8,9,11,12,13,14,15,16]

Summary

Introduction

Water vapor is the most abundant greenhouse gas and is routinely measured in atmospheric chemistry research [1,2,3]. The use of this 1.37 μm H2O line originated from a dedicated line selection process and test measurements [3,11,17], as well as the availability of fairly low-cost (compared to the mid-infrared MIR) near-infrared optical elements and detectors from telecom mass applications that are available with excellent performance parameters This is true for the fiber-coupled diode lasers [13] that spurred the development of very compact field-compatible laser hygrometers [5,11,14]. Regarding H2O line data, collisional broadening coefficients are required for spectroscopic measurements, e.g., those based on dTDLAS and similar spectroscopic techniques, where the absorption line has to be modeled (due to potential variations in the gas pressure, temperature or matrix during the measurements), e.g., with a Voigt profile. For air broadening and temperature dependence measurements, separate gas cells (and modified spectroscopic systems) are used

H2O Collisional Broadening Measurements

Findings

Discussion

Conclusions