the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Aug 2026
Transport of anthropogenic CH2Cl2-rich air from Asia across the North Pacific
Abstract. Dichloromethane (CH2Cl2) is emitted mainly anthropogenically and suspected to delay stratospheric ozone recovery. We present in detail the first retrievals of mesoscale 2D distributions of CH2Cl2 from infrared limb observations. The airborne remote sensing instrument GLORIA-AB (Gimballed Limb Observer for Radiance Imaging of the Atmosphere, hereinafter “GLORIA”) was deployed aboard the German research aircraft HALO during the PHILEAS campaign in August and September 2023 to study the outflow of the Asian Summer Monsoon (ASM). During long-range flights from Alaska, GLORIA observed filaments with elevated CH2Cl2 above the North Pacific, Canada and Alaska. Filaments with horizontal extents along the flight track of up to ~1000 km and CH2Cl2 volume mixing ratios of locally up to ~400 pptv were observed in the free troposphere, corresponding to levels more than six times higher than the northern hemispheric background for that season. Moderate CH2Cl2 enhancements were detected locally also in air masses with characteristics of the extra-tropical lowermost stratosphere. We applied new high-resolution CH2Cl2 spectroscopic data, resulting in ~11 % lower volume mixing ratios than in previous analyses using commonly available absorption cross sections. The GLORIA measurements are consistent with in situ observations on HALO by HAGAR-V and GhOST. Using back-trajectory analysis and surface-origin tracers by the CLaMS model, observed filaments are traced back to the ASM region and potential source regions are identified. Mesoscale filaments are shown to rapidly transport substantial amounts of CH2Cl2 from the ASM across the North Pacific into the Northern Hemisphere Upper Troposphere and Lower Stratosphere (UTLS).
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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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RC1: 'Comment on egusphere-2026-3271', Theodore Koenig, 28 Sep 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3271/egusphere-2026-3271-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2026-3271-RC1 -
RC2: 'Comment on egusphere-2026-3271', Anonymous Referee #2, 26 Oct 2026
Based on the PHILEAS campaign, this study presents detailed 2D infrared limb observations of the mesoscale distribution of CH2Cl2 along the research flights, and uses back trajectories together with surface-origin tracers to identify the origin of CH2Cl2-rich filaments. These analyses provide useful information for understanding CH2Cl2 transport and its potential implications for stratospheric ozone. I suggest that more details on the retrieval and validation of the observations be provided to support the analysis.
Section 2.2 and Figure 2: I would like to see the averaging kernels (AKs) for representative CH2Cl2 retrievals. Figure 2 shows the vertical resolution and estimated errors, but the AKs would help assess the sensitivity and vertical smoothing of the retrieved profiles, especially near flight level.
Section 4 and Appendix B: I believe time differences between the GLORIA and in situ measurements may also affect the comparison, but this is not sufficiently discussed in the manuscript. Please provide more details on the time differences and their impact on the comparison and validation (whether there are advection and evolution affecting the comparison). I suggest the authors also provide a more detailed explanation of why the discrepancies are more pronounced in section C, since sections A and B are derived using the same retrieval method and are subject to the same sampling geometry and resolution limitations.
Section 5.3: Are Korea and Japan included in the surface-origin tracer setup? I am also curious whether emissions from these regions could contribute to the observed CH2Cl2-rich filaments.
Lines 45–46: Hydrofluorocarbon production should be considered part of chemical synthesis and therefore should not be listed as a separate, parallel category.
Line 58: It is not appropriate to describe the increased CH2Cl2 abundances as “unexplained,” since they are largely attributable to increasing usage.
Line 71: The phrase “no CH2Cl2 emissions” is ambiguous. The authors should clarify whether this refers to an assumed absence of emissions after 2019.
Lines 86–110: Given the substantial similarity in the conclusions of the cited studies, this overview should be condensed to avoid redundancy.
Lines 152–156: Do the authors mean “flight route planning”?
Figures 3-5: Please use consistent color scales in panels (a) and (b), and avoid using black for both the lowest and highest values in panel (a).
Figure 4: There are several crossing points near the labels II and III. The flight routes (direction) corresponding to these labels should be clarified.
Figure 6a: could the authors indicate the locations of A and B by explicit labels (dots) or annotations?
Citation: https://doi.org/10.5194/egusphere-2026-3271-RC2
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