Sources of error in open-path FTIR measurements of N<sub>2</sub>O and CO<sub>2</sub> emitted from agricultural fields

Lin, Cheng-Hsien; Grant, Richard H.; Heber, Albert J.; Johnston, Cliff T.

doi:https://doi.org/10.5194/amt-13-2001-2020

Articles | Volume 13, issue 4

https://doi.org/10.5194/amt-13-2001-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-13-2001-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 4

Research article

|

21 Apr 2020

Research article |

| 21 Apr 2020

Sources of error in open-path FTIR measurements of N₂O and CO₂ emitted from agricultural fields

Cheng-Hsien Lin, Richard H. Grant, Albert J. Heber, and Cliff T. Johnston

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Final revised paper (published on 21 Apr 2020)
Supplement to the final revised paper
Preprint (discussion started on 12 Aug 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review', Anonymous Referee #1, 21 Aug 2019
- AC1: 'Responses for the anonymous referee #1', CHENG-HSIEN LIN, 05 Oct 2019
RC2: 'Review', Anonymous Referee #2, 24 Aug 2019
- AC2: 'Responses for the anonymous referee #2', CHENG-HSIEN LIN, 05 Oct 2019
- AC3: '2nd Responses for the anonymous referee #2', CHENG-HSIEN LIN, 17 Oct 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by CHENG-HSIEN LIN on behalf of the Authors (17 Oct 2019) Author's response Manuscript

ED: Reconsider after major revisions (28 Oct 2019) by David Griffith

AR by CHENG-HSIEN LIN on behalf of the Authors (07 Dec 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (04 Feb 2020) by David Griffith

The manuscript is much improved after addressing the referees’ comments. It can be published after addressing the following minor comments. Page and line numbers refer to Author response V3.pdf.

Throughout – ppmv and ppbv are not concentrations (ie amount per volume), they are mole fractions. It is OK to use “concentration” in a general sense, but not when referring to specific ppm or ppb values – please use “mole fraction” in these (many) cases throughout.
P14L23 – CO2 is also a significant GHG from agriculture
P16L6 omit “ OP-FTIR measurements … instrument . Consequently”
P16 L24 MALT is just one example of the NLLS/forward modelling approach, you could also mention the forward model you have used, E-trans from ONTAR Corp. (Note this was not mentioned in earlier versions of the MS, but is now specified P19 L20).
P16 L32 Griffith 2009 seems to be missing from the rferences.
P18L4. Given that this is a quantitative study it is important to specify ACCURACY of reference measurements. Here, what is the accuracy of the diluter? How accurate are the figure od 30ppmv, 310.0, 400.0, 500.0, 600.0, 700.0 ppbv? Is the nnn.0 significant figure really correct?
P19 L20. To be clear with the ambiguity of specifying zero filling, I suggest adding …no zero filling (ie spectral datapoint spacing ~ 0.25 cm-1)
P19 L20. How often were the stray light spectra measured (they may change with time and temperature). P20L11. Could you please clarify if for the OP spectra you have used IMACC software to build and use the CLS and PLS models, rather than TQ Analyst as used for the lab spectra. Why use two different packages?
P20L30. As above, please specify the certified accuracy (not precision) of the reference CO2 and N2O measurements.
P24 L19. How were the reference mole fractions for the path length study determined? Are they from the S-OPS over 50 m? Please be explicit, also with the accuracy of the assumption that the S-OPS values can be extrapolated over the longer 100 and 150 m paths.

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AR by CHENG-HSIEN LIN on behalf of the Authors (13 Feb 2020) Author's response Manuscript

ED: Publish as is (21 Feb 2020) by David Griffith

Short summary

Gas quantification using the open-path Fourier transform infrared spectrometer (OP-FTIR) is subject to interferences of environmental variables, leading to errors in gas concentration calculations. This study investigated the effects of ambient water vapour content, temperature, path lengths, and wind speed on the quantification of N₂O and CO₂ concentrations, which can help the OP-FTIR users to avoid these errors and improve the precision and accuracy of the atmospheric gas quantification.

Sources of error in open-path FTIR measurements of N2O and CO2 emitted from agricultural fields

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Interactive discussion

Peer-review completion

Sources of error in open-path FTIR measurements of N₂O and CO₂ emitted from agricultural fields