the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Apr 2025
Tracing Ammonia Emission Sources in California's Salton Sea Region: Insights from Airborne Longwave-Infrared Hyperspectral Imaging and Ground Monitoring
Abstract. Ammonia (NH3) plays an important role in atmospheric chemistry and air quality, but its emissions remain poorly constrained due to its short atmospheric lifetime, high spatial heterogeneity, and limited coverage of existing monitoring resources. This study integrates airborne longwave-infrared (LWIR) hyperspectral imaging at ~2 m spatial resolution with ground-based stationary and mobile in-situ measurements to map and characterize NH3 emissions in two regions near the Salton Sea in Southern California: Mecca in the northwest and Imperial in the southeast. Airborne surveys conducted in March and September 2023 with a wide-swath LWIR spectra imager revealed pronounced spatial and seasonal variability. Average NH3 levels in Imperial were 2.5 to 8 times higher than those in Mecca, linked primarily to large, concentrated animal feeding operations (CAFOs), geothermal power plants, fumaroles, and intensive agricultural activities. Ground-based mobile monitoring corroborated these findings, showing elevated NH3 levels near these sources and especially high NH3 concentrations downwind of CAFOs with large cattle populations. The results underscore the utility of airborne LWIR hyperspectral imaging in detecting and mapping NH3 at hyperlocal scales, including sources absent from existing inventories. They further highlight the need for routine airborne campaigns and the development of next-generation satellite missions with higher spatial resolution to achieve comprehensive, large-area monitoring. These findings inform air quality management strategies and emphasize the importance of improving emission inventories for effective mitigation of NH3-driven air pollution.
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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.
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Preprint
(4466 KB)
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Supplement
(3951 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(4466 KB) - Metadata XML
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Supplement
(3951 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1378', Anonymous Referee #1, 23 Apr 2025
- AC1: 'Reply on RC1', Sina Hasheminassab, 18 Jun 2025
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RC2: 'Comment on egusphere-2025-1378', Anonymous Referee #2, 03 May 2025
This study presents measurements of atmospheric ammonia using ground-based and air-borne measurements at two different US cites. The study is more suitable for “Atmospheric Measurement Techniques” than ACP, but can be considered as a “Measurement Report” in ACP. The MS is relatively well-written and the measurements are valuable, but a substantial revision is necessary before it can be accepted for a publication.
Major points:
- Introduction has to be enhanced with recent regional and global studies on atmospheric ammonia and policies related to it. The authors now list only two such studies, which are not enough for an Introduction to any study such studies. One example for a recent study is https://doi.org/10.1016/j.jclepro.2023.140424 and has to be cited.
- Please compare your measurements with other available satellite or model results. Although the unit of NH3 is different, you could still compare the general features.
- What are the reasons for the diurnal variations of atmospheric ammonia (Figure 3)? However, this difference is not observed in Figure 2?
- Why the meteorological data are taken from a model output? No AWS or measurements are available? How good are these model results? What is the horizontal resolution of the model? Did you interpolate the model results to the flight tracks?
- What are the reason for the March and September NH3 differences (L380-390)?
- Need a discussion of the limitation of the analysis and uncertainty of the retrievals.
Minor issues:
L60: and AIRS
L284-285: What is the scale that you are talking about? Mention this here
Citation: https://doi.org/10.5194/egusphere-2025-1378-RC2 - AC2: 'Reply on RC2', Sina Hasheminassab, 18 Jun 2025
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1378', Anonymous Referee #1, 23 Apr 2025
This manuscript integrates airborne, ground-based, and mobile measurements to map NH3 emissions in two source regions in California. The paper is well written and the structure is clear. The results are important for improving the ammonia emission inventories. I only have minor comments as follows:
Presentation issues:
Section 3.1: Please quantitatively summarize the overall performance of airborne measurements to identify emissions sources, e.g., how many CAFOs/GPPs could be identified.
Figure 8: I am not sure if plume A to I were chosen based on the time series or emission sources - please clarify.
Figure 9: There is no marked source in plume A. I suggest switching the colorbar to log scale and using the size of the marker to denote cattle population for each CAFO facility. Also, please add latitudes, longitudes, and wind direction for each panel.
Discussions: It would be helpful to compare the resolution of satellite maps versus airborne measurements in this study to highlight the advantage of this study.
Conclusions: I recommend stating the conclusions more quantitatively.
Minor comments:
Line 35: add citation
Line 38: Please cite commonly used ammonia emission inventories here besides Zeng et al., 2018
Line 57: needs citation for the first sentence of the paragraph
Line 160: Please briefly discuss the detection limit and validation results here instead of referring to the literature
Citation: https://doi.org/10.5194/egusphere-2025-1378-RC1 - AC1: 'Reply on RC1', Sina Hasheminassab, 18 Jun 2025
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RC2: 'Comment on egusphere-2025-1378', Anonymous Referee #2, 03 May 2025
This study presents measurements of atmospheric ammonia using ground-based and air-borne measurements at two different US cites. The study is more suitable for “Atmospheric Measurement Techniques” than ACP, but can be considered as a “Measurement Report” in ACP. The MS is relatively well-written and the measurements are valuable, but a substantial revision is necessary before it can be accepted for a publication.
Major points:
- Introduction has to be enhanced with recent regional and global studies on atmospheric ammonia and policies related to it. The authors now list only two such studies, which are not enough for an Introduction to any study such studies. One example for a recent study is https://doi.org/10.1016/j.jclepro.2023.140424 and has to be cited.
- Please compare your measurements with other available satellite or model results. Although the unit of NH3 is different, you could still compare the general features.
- What are the reasons for the diurnal variations of atmospheric ammonia (Figure 3)? However, this difference is not observed in Figure 2?
- Why the meteorological data are taken from a model output? No AWS or measurements are available? How good are these model results? What is the horizontal resolution of the model? Did you interpolate the model results to the flight tracks?
- What are the reason for the March and September NH3 differences (L380-390)?
- Need a discussion of the limitation of the analysis and uncertainty of the retrievals.
Minor issues:
L60: and AIRS
L284-285: What is the scale that you are talking about? Mention this here
Citation: https://doi.org/10.5194/egusphere-2025-1378-RC2 - AC2: 'Reply on RC2', Sina Hasheminassab, 18 Jun 2025
Peer review completion
Journal article(s) based on this preprint
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Sina Hasheminassab
David M. Tratt
Olga V. Kalashnikova
Clement S. Chang
Morad Alvarez
Kerry N. Buckland
Michael J. Garay
Francesca M. Hopkins
Eric R. Keim
Yaning Miao
Payam Pakbin
William C. Porter
Mohammad H. Sowlat
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(4466 KB) - Metadata XML
-
Supplement
(3951 KB) - BibTeX
- EndNote
- Final revised paper
This manuscript integrates airborne, ground-based, and mobile measurements to map NH3 emissions in two source regions in California. The paper is well written and the structure is clear. The results are important for improving the ammonia emission inventories. I only have minor comments as follows:
Presentation issues:
Section 3.1: Please quantitatively summarize the overall performance of airborne measurements to identify emissions sources, e.g., how many CAFOs/GPPs could be identified.
Figure 8: I am not sure if plume A to I were chosen based on the time series or emission sources - please clarify.
Figure 9: There is no marked source in plume A. I suggest switching the colorbar to log scale and using the size of the marker to denote cattle population for each CAFO facility. Also, please add latitudes, longitudes, and wind direction for each panel.
Discussions: It would be helpful to compare the resolution of satellite maps versus airborne measurements in this study to highlight the advantage of this study.
Conclusions: I recommend stating the conclusions more quantitatively.
Minor comments:
Line 35: add citation
Line 38: Please cite commonly used ammonia emission inventories here besides Zeng et al., 2018
Line 57: needs citation for the first sentence of the paragraph
Line 160: Please briefly discuss the detection limit and validation results here instead of referring to the literature