the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jun 2025
New quantitative measurements and spectroscopic line parameters of ammonia in the 685–1250 cm-1 spectral region for atmospheric remote sensing
Abstract. Ammonia (NH3) is a toxic pollutant, generally linked to agricultural emissions, and plays a major role in the formation of fine aerosols which have a significant and detrimental effect on human health. NH3 is one of the key pollutants that can be monitored by satellite instruments orbiting the Earth, including the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS). The interpretation of these measured atmospheric spectra requires accurate radiative transfer modelling, which relies on the quality of the input spectroscopic line parameters.
In this work we present new high quality high-resolution infrared spectra of self- and air-broadened NH3 at 296 K using a Bruker IFS 125HR spectrometer and a 24.45 cm pathlength sample cell with silver chloride windows. Using a multispectrum fitting approach, we then determine new spectroscopic line parameters over the range 685 cm-1 to 1250 cm-1 for the NH3 0100 00 0 s ← 0000 00 0 a and 0100 00 0 a ← 0000 00 0 s transitions associated with the ν2 mode; the Q branches of these transitions are the strongest NH3 features observed in atmospheric spectra. Our analysis utilises the Voigt lineshape, with speed-dependent Voigt and Rosenkranz line mixing for the strongest lines. To date this is the most complete experimental and multispectrum analysis of air-broadened NH3 over this spectral region. Our derived spectroscopic line parameters reproduce the new measurements substantially better than line parameters from the HITRAN 2020 database, which were derived from a mixture of ab initio calculations and previous laboratory measurements. We have revised values for parameters such as line intensities and air-broadened Lorentz halfwidths, in some cases by almost 10 %. We have substantially lowered the uncertainties of key parameters, such as line intensities. In addition to the measured speed dependence and Rosenkranz line mixing parameters, which we believe are the first reported for the ν2 band of NH3 in air, we also determine a range of parameters for the ν2 band that are not currently in HITRAN, for example self- and air-pressure-induced shifts. We expect these new parameters to provide a more accurate basis for incorporation into atmospheric radiative transfer models to measure NH3 concentrations from satellite.
-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(2113 KB)
-
Supplement
(5646 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2113 KB) - Metadata XML
-
Supplement
(5646 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-2514', Chris Boone, 04 Jul 2025
- AC1: 'Reply on RC1', Daniel Coxon, 18 Aug 2025
-
RC2: 'Comment on egusphere-2025-2514', Anonymous Referee #2, 13 Jul 2025
- AC2: 'Reply on RC2', Daniel Coxon, 18 Aug 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-2514', Chris Boone, 04 Jul 2025
This article describes the generation of a new set of spectroscopic parameters for NH3. It is careful and solid work, and the article is well written. The study seems quite complete other than the lack of temperature dependence, which could play a role in the analysis of atmospheric measurements somewhere other than near the surface; for example, with retrievals using MIPAS or ACE-FTS measurements in the upper troposphere where temperatures are quite different from 296 K.
The lack of temperature effects in the analysis might not be a major problem for pressure broadening parameters (in that pressure broadening temperature dependence information is already available in HITRAN for NH3 lines) or pressure shifts (in that it is typically assumed that pressure shifts have no temperature dependence). The biggest question might be the temperature dependence of speed dependence (through the parameter aw). Assuming that aw is constant as a function of temperature would imply that Γ0 and Γ2 have an identical temperature dependence, which may not be the case. This is not an issue that needs to be addressed in this paper, though.
I am wondering if Γ2 values derived in this study (using the formalism in Eqs 8 and 9) can be directly used with the “quadratic speed dependent Voigt” formalism used elsewhere in the literature, expressed as the difference between two Voigt-like expressions. Software that uses line-by-line calculations seem more likely to employ the quadratic speed dependent Voigt formalism because it does not involve numerical evaluation of the integral over velocity, which should make it more efficient to calculate. This likely does not matter for IASI, CrIS, and TES (the suggested end users of the new parameters) because they presumably employ look up tables instead of line-by-line calculations, which means there would only be a one-time cost from the extra calculation requirements when populating the look up tables. I expect the two formalisms are compatible, differing only in the order of integration over velocity for the double integral associated with speed dependent Voigt (i.e., integrating over velocity first for “quadratic speed dependent Voigt” as compared to integrating over velocity second for the LabVIEW formalism described in the paper), but that is an assumption.
Note that a paper has been submitted (still under review) titled “New beyond-Voigt line-shape profile recommended for the HITRAN database by P. Wcislo et al” meant to guide future non-Voigt parameter usage in HITRAN. For speed dependent Voigt, the suggested “official HITRAN” line shape (the modified Hartmann Tran profile) will be the difference between two Voigt-like expressions.
Some people may continue to employ Voigt line shapes rather than switching to more accurate non-Voigt calculations. HITRAN has separate database streams for Voigt and non-Voigt, so you might want to consider what users will get if they request a set of Voigt profile parameters for NH3 from HITRAN after your data have been inserted. Will it be the older data set that contains no lines with non-Voigt parameters (and therefore none of your data)? Will it be your data for weaker lines and older data for the strongest lines (because the strongest lines use speed dependent Voigt in your data set)? Will it be all your data with non-Voigt parameters like speed dependence simply stripped out (which would make pressure broadening parameters too large, so I can’t imagine them going that route)? If you want to completely replace the old NH3 parameters, you might need to consider providing HITRAN with two sets of parameters: a “Voigt set” and a “speed-dependent Voigt set.” That would require extra work on your part, of course.
Nothing discussed here requires edits to the article. The only technical change I would suggest is to put the references in alphabetical order to make them easier to parse.
Citation: https://doi.org/10.5194/egusphere-2025-2514-RC1 - AC1: 'Reply on RC1', Daniel Coxon, 18 Aug 2025
-
RC2: 'Comment on egusphere-2025-2514', Anonymous Referee #2, 13 Jul 2025
- AC2: 'Reply on RC2', Daniel Coxon, 18 Aug 2025
Peer review completion
Journal article(s) based on this preprint
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 693 | 56 | 28 | 777 | 53 | 22 | 39 |
- HTML: 693
- PDF: 56
- XML: 28
- Total: 777
- Supplement: 53
- BibTeX: 22
- EndNote: 39
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Daniel John Luke Coxon
Jeremy J. Harrison
D. Chris Benner
V. Malathy Devi
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2113 KB) - Metadata XML
-
Supplement
(5646 KB) - BibTeX
- EndNote
- Final revised paper
This article describes the generation of a new set of spectroscopic parameters for NH3. It is careful and solid work, and the article is well written. The study seems quite complete other than the lack of temperature dependence, which could play a role in the analysis of atmospheric measurements somewhere other than near the surface; for example, with retrievals using MIPAS or ACE-FTS measurements in the upper troposphere where temperatures are quite different from 296 K.
The lack of temperature effects in the analysis might not be a major problem for pressure broadening parameters (in that pressure broadening temperature dependence information is already available in HITRAN for NH3 lines) or pressure shifts (in that it is typically assumed that pressure shifts have no temperature dependence). The biggest question might be the temperature dependence of speed dependence (through the parameter aw). Assuming that aw is constant as a function of temperature would imply that Γ0 and Γ2 have an identical temperature dependence, which may not be the case. This is not an issue that needs to be addressed in this paper, though.
I am wondering if Γ2 values derived in this study (using the formalism in Eqs 8 and 9) can be directly used with the “quadratic speed dependent Voigt” formalism used elsewhere in the literature, expressed as the difference between two Voigt-like expressions. Software that uses line-by-line calculations seem more likely to employ the quadratic speed dependent Voigt formalism because it does not involve numerical evaluation of the integral over velocity, which should make it more efficient to calculate. This likely does not matter for IASI, CrIS, and TES (the suggested end users of the new parameters) because they presumably employ look up tables instead of line-by-line calculations, which means there would only be a one-time cost from the extra calculation requirements when populating the look up tables. I expect the two formalisms are compatible, differing only in the order of integration over velocity for the double integral associated with speed dependent Voigt (i.e., integrating over velocity first for “quadratic speed dependent Voigt” as compared to integrating over velocity second for the LabVIEW formalism described in the paper), but that is an assumption.
Note that a paper has been submitted (still under review) titled “New beyond-Voigt line-shape profile recommended for the HITRAN database by P. Wcislo et al” meant to guide future non-Voigt parameter usage in HITRAN. For speed dependent Voigt, the suggested “official HITRAN” line shape (the modified Hartmann Tran profile) will be the difference between two Voigt-like expressions.
Some people may continue to employ Voigt line shapes rather than switching to more accurate non-Voigt calculations. HITRAN has separate database streams for Voigt and non-Voigt, so you might want to consider what users will get if they request a set of Voigt profile parameters for NH3 from HITRAN after your data have been inserted. Will it be the older data set that contains no lines with non-Voigt parameters (and therefore none of your data)? Will it be your data for weaker lines and older data for the strongest lines (because the strongest lines use speed dependent Voigt in your data set)? Will it be all your data with non-Voigt parameters like speed dependence simply stripped out (which would make pressure broadening parameters too large, so I can’t imagine them going that route)? If you want to completely replace the old NH3 parameters, you might need to consider providing HITRAN with two sets of parameters: a “Voigt set” and a “speed-dependent Voigt set.” That would require extra work on your part, of course.
Nothing discussed here requires edits to the article. The only technical change I would suggest is to put the references in alphabetical order to make them easier to parse.