the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Aug 2026
Evaluating satellite limb measurements of nitrous oxide
Abstract. As of the early 2000s, multiple contemporaneous global and vertically resolved nitrous oxide (N2O) datasets have become available from a suite of limb-viewing satellite instruments. Together, these datasets provide a 23-year and counting continuous N2O record. Due to its long lifetime, N2O is a valuable tracer of atmospheric transport, and a reliable long-term record therefore allows the examination of changes in stratospheric circulation as a result of climate change. In order to combine results from different satellite datasets for these purposes, it is necessary to account for their biases, which can be determined through evaluation studies. Here, N2O measurements in the upper troposphere and lower-to-middle stratosphere (5–40 km) are evaluated from five different satellite limb sounders: ACE-FTS on SCISAT, HIRDLS and MLS on Aura, MIPAS on Envisat, and SMR on Odin. This is done by comparing colocated satellite measurements with each other to determine the instruments’ relative biases and by comparing each dataset with independent reference data from balloon-borne instruments. ACE-FTS (v5.2), the two MIPAS datasets (V8), and SMR (v3.0.0) agree within ±5–10 %, but HIRDLS (v07) has variable performance depending on the region and time of year. MLS (v5) has a persistent deviation resulting in a low bias of up to 30 % in the lower stratosphere at 24 km. This bias is substantially reduced in v6. These findings are corroborated by the comparisons of each satellite instrument with balloon-borne data. This study lays the groundwork for creating a merged and bias-corrected N2O time series spanning from 2002 to the present using ACE-FTS, MIPAS, SMR, and possibly the MLS v6 dataset.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 07 Oct 2026)
- RC1: 'Comment on egusphere-2026-4651', Xin Zhou, 19 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-4651', Anonymous Referee #2, 21 Sep 2026
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Dear authors, please see the attached file for the comments.
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RC3: 'Comment on egusphere-2026-4651', Anonymous Referee #3, 21 Sep 2026
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4651/egusphere-2026-4651-RC3-supplement.pdf
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- 1
Summary:
Nitrous oxide (N₂O) is an important greenhouse gas and a major contributor to stratospheric ozone depletion. It is also a useful trace gas for diagnosing changes in stratospheric transport. Therefore, accurate long-term observations of stratospheric N₂O from satellite and in situ measurements are particularly valuable.
The paper by Saunders et al. provides a comprehensive assessment of satellite limb measurements of N₂O, covering a continuous 23-year global record, through intercomparison among different satellite instruments and validation against independent balloon measurements. This work provides a valuable starting point for studies using these satellite profiles, particularly those investigating long-term changes in stratospheric transport and composition. The paper is generally well written, and I think it is suitable for publication in AMT. My major comment concerns the organization of the two sections on “intercomparison” and “validation”, which I elaborate on below, together with several technical comments.
Major comment
1. Organization of the “intercomparison” and “validation” sections
I do not think it is helpful to separate the “validation” from the “intercomparison” in the current way. When comparing N₂O profiles from different satellite instruments, readers would naturally want to know both how the satellite datasets differ from one another and how well each of them agrees with independent balloon measurements.
In the current structure, the satellite intercomparison is presented first, with SMR used as the reference for evaluating differences among the satellite datasets. However, at this stage, the reader does not yet know how well SMR itself agrees with the independent balloon observations, or whether there is sufficient justification for using it as the reference. This makes the interpretation of the satellite intercomparison somewhat difficult. For example, a difference between another satellite dataset and SMR does not by itself indicate which dataset is closer to the independent observations.
I therefore suggest reconsidering the organization of these two sections. At a minimum, it would seem more logical to present the validation against the independent balloon measurements before the satellite intercomparison. Alternatively, the authors could integrate the validation and intercomparison more closely, so that the differences among satellite datasets can be interpreted alongside their respective agreement with independent observations.
Technical comments
1. Line 251: “MLS v5 has a clear low bias from about 20–27 km.”
The wording “low bias” is potentially confusing. It could be interpreted as meaning that MLS v5 has a small bias, rather than that MLS v5 is biased low relative to the reference. I suggest using wording such as “MLS v5 shows a clear negative bias” or “MLS v5 is biased low from approximately 20 to 27 km.” This would also be more consistent with the subsequent discussion, where MLS v5 is identified as an outlier over much of this altitude range.
2. Line 254: “unphysical features”
Please be more specific about what the “unphysical features” are. What features of the retrieved profiles are considered unphysical, and on what basis are they identified as such?
3. Figure 12:
The biases above approximately 25 km generally have opposite signs for MLS v5 and MLS v6. What causes this substantial change between the two MLS versions? Is it related to changes in the retrieval algorithm, spectroscopy, calibration, or other aspects of the processing? Given that MLS provides an important long-term N₂O record, I think this difference deserves some discussion.