Emissions of greenhouse gases from a North American megacity
Open accessAbstract
Atmospheric column abundances of carbon dioxide (CO 2), carbon monoxide (CO), methane (CH 4) and nitrous oxide (N 2 O) have been measured above the South Coast air basin (SCB), a densely populated urban region of Southern California, USA, which includes Los Angeles and the surrounding suburbs. Large diurnal variations in CO and CH 4 are observed which correlate well with those in CO 2. Weaker correlations are seen between N 2 O and CO 2, with large uncertainties. We compute yearly SCB emissions of CO and CH 4 to be 1.4 ± 0.3 Tg CO and 0.6 ± 0.1 Tg CH 4. We compare our calculated emissions to the California Air Resources Board (CARB) and the Emission Database for Global Atmospheric Research (EDGAR) estimates. Our measurements confirm that urban emissions are a significant source of CH 4 and in fact may be substantially higher than currently estimated. If our emissions are typical of other urban centers, these findings suggest that urban emissions could contribute 7–15% to the global anthropogenic budget of methane.
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Other column-based studies determined XCH4/XCO2 for urban sources in Los Angeles ranging from 6.65 to 9.96 ppb/ppm in 2015 and 11 ± 2 ‰ in 2008.
“Other column-based studies have determined the X CH 4 /X CO 2 for urban sources in the Los Angeles city, finding ratios ranging from 6.65 to 9.96 (ppb/ppm) in 2015 (Chen et al., 2016) and 11 ± 2 ‰ in 2008 (Wunch et al., 2009).”
From Ground solar absorption observations of total column CO, CO <sub>2</sub> , CH <sub>4</sub> , and aerosol optical depth from California's Sequoia Lightning Complex Fire: emission factors and modified combustion efficiency at regional scales (2023) · cites this paper as Wunch et al., 2009
Table 1 (Summary and Conclusions) gives the xCH₄-to-xCO₂ anomaly slope as 7.8 ± 0.8‰, not 11 ± 2‰. The 11 ± 2‰ value belongs to xCO-to-xCO₂. This verdict concerns only the Wunch et al. value, not the separately cited 2015 range. (LLM, conf=0.90)
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Experimental — accuracy not yet measuredUrban fossil fuel and wildfire XCH4/XCO2 ratios are very similar due to incomplete combustion and are not distinct enough to separate.
“Wunch et al. (2009) determined that urban fossil fuel and wildfire X CH 4 /X CO 2 ratios are very similar due to incomplete combustion, and the ratios are not distinct enough to separate.”
From Ground solar absorption observations of total column CO, CO <sub>2</sub> , CH <sub>4</sub> , and aerosol optical depth from California's Sequoia Lightning Complex Fire: emission factors and modified combustion efficiency at regional scales (2023) · cites this paper as Wunch et al., 2009
The Methods (§2, paragraph 10; page unavailable) say wildfire-affected days were excluded because they had large CO contributions. The Introduction (§1, paragraph 2; page unavailable) links incomplete combustion to CO, not to an XCH4/XCO2 ratio. Searches for wildfire–fossil-fuel ratio comparisons found no passage saying their XCH4/XCO2 ratios are similar or cannot distinguish the sources. (LLM, conf=0.76)
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Cited by
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Differential column measurements using compact solar-tracking spectrometers
Chen, J., Viatte, C., Hedelius, J. K., Jones, T., Franklin, J. E., Parker, H., Gottlieb, E. W., Wennberg, P. O., Dubey, M. K., & Wofsy, S. C. (2016) · Atmospheric Chemistry and Physics · doi:10.5194/acp-16-8479-2016 · Cited by 143 · see citing works
Self-citationFrausto-Vicencio, I., Heerah, S., Meyer, A. G., Parker, H. A., Dubey, M., & Hopkins, F. M. (2023) · Atmospheric Chemistry and Physics · doi:10.5194/acp-23-4521-2023 · Cited by 10 · see citing works
- Authors
- Wunch, D., Wennberg, P. O., Toon, G. C., Keppel‐Aleks, G., & Yavin, Y. G.
- Affiliations
- California Institute of Technology (US)
- Venue
- Geophysical Research Letters
- Publisher
- American Geophysical Union (AGU)
- Published
- 2009-08-06
- Volume
- 36
- Issue
- 15
- ISSN
- 0094-8276 (ISSN-L)
- 1944-8007
- OpenAlex
- W1809408372
- Cited by
- 271
- References
- 0
- Citations by year
- 2026: 5 · 2025: 12 · 2024: 21 · 2023: 24 · 2022: 12 · 2021: 19 · 2020: 13 · 2019: 20 · 2018: 11 · 2017: 18 · 2016: 20 · 2015: 19 · 2014: 27 · 2013: 18 · 2012: 14
- FWCI
- 9.17
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Geophysical Research Letters (publishedVersion)
- CaltechAUTHORS (California Institute of Technology) (submittedVersion)
- Funders
- National Aeronautics and Space Administration
- California Institute of Technology
- National Oceanic and Atmospheric Administration
- Jet Propulsion Laboratory
- Topics
- Physical Sciences › Environmental Science › Global and Planetary Change › Atmospheric and Environmental Gas Dynamics
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Atmospheric chemistry and aerosols
- Physical Sciences › Chemistry › Spectroscopy › Spectroscopy and Laser Applications
- Keywords
- greenhouse gas emissions, urban emissions, methane, carbon monoxide, carbon dioxide, nitrous oxide, South Coast Air Basin, Los Angeles, diurnal variation, emission estimates, EDGAR
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