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Large and seasonally varying biospheric CO 2 fluxes in the Los Angeles megacity revealed by atmospheric radiocarbon. Proc Natl Acad Sci U S A 2020; 117:26681-26687. [PMID: 33046637 DOI: 10.1073/pnas.2005253117] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Measurements of Δ14C and CO2 can cleanly separate biogenic and fossil contributions to CO2 enhancements above background. Our measurements of these tracers in air around Los Angeles in 2015 reveal high values of fossil CO2 and a significant and seasonally varying contribution of CO2 from the urban biosphere. The biogenic CO2 is composed of sources such as biofuel combustion and human metabolism and an urban biospheric component likely originating from urban vegetation, including turf and trees. The urban biospheric component is a source in winter and a sink in summer, with an estimated amplitude of 4.3 parts per million (ppm), equivalent to 33% of the observed annual mean fossil fuel contribution of 13 ppm. While the timing of the net carbon sink is out of phase with wintertime rainfall and the sink seasonality of Southern California Mediterranean ecosystems (which show maximum uptake in spring), it is in phase with the seasonal cycle of urban water usage, suggesting that irrigated urban vegetation drives the biospheric signal we observe. Although 2015 was very dry, the biospheric seasonality we observe is similar to the 2006-2015 mean derived from an independent Δ14C record in the Los Angeles area, indicating that 2015 biospheric exchange was not highly anomalous. The presence of a large and seasonally varying biospheric signal even in the relatively dry climate of Los Angeles implies that atmospheric estimates of fossil fuel-CO2 emissions in other, potentially wetter, urban areas will be biased in the absence of reliable methods to separate fossil and biogenic CO2.
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Gurney KR, Song Y, Liang J, Roest G. Toward Accurate, Policy-Relevant Fossil Fuel CO 2 Emission Landscapes. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:9896-9907. [PMID: 32806921 DOI: 10.1021/acs.est.0c01175] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The bottom-up (BU) approach has been used to develop spatiotemporally resolved, sectorally disaggregated fossil fuel CO2 (FFCO2) emission data products. These efforts are critical constraints to atmospheric assessment of anthropogenic fluxes in addition to offering the climate change policymaking community usable information to guide mitigation. In the United States, there are two high-resolution FFCO2 emission data products, Vulcan and the Anthropogenic Carbon Emissions System (ACES). As a step toward developing improved, accurate, and detailed FFCO2 emission landscapes, we perform a comparison of the two data products. We find that while agreeing on total FFCO2 emissions at the aggregate scale (relative difference = 1.7%), larger differences occur at smaller spatial scales and in individual sectors. Differences in the smaller-emitting sectors are likely errors in ACES input data or emission factors. ACES advances the approach for estimating emissions in the gas and oil sector, while Vulcan shows better geocoordinate correction in the electricity production sector. Differences in the subcounty residential and commercial building sectors are driven by different spatial proxies and suggest a task for future investigation. The gridcell absolute median relative difference, a measure of the average gridcell-scale relative difference, indicates a 53.5% difference. The recommendation for improved BU granular FFCO2 emission estimation includes review, assessment, and archive of point source geolocations, CO emission input data, CO and CO2 emission factors, and uncertainty approaches including those due to spatial errors. Finally, intensives where local utility data are publicly available could test the spatial proxies used in estimating residential and commercial building emissions. These steps toward best practices will lead to more accurate, granular emissions, enabling optimal emission mitigation policy choices.
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Affiliation(s)
- Kevin Robert Gurney
- School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, Arizona 85287, United States
- School of Life Sciences, Arizona State University, Tempe, Arizona 85281, United States
| | - Yang Song
- School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, Arizona 85287, United States
| | - Jianming Liang
- School of Life Sciences, Arizona State University, Tempe, Arizona 85281, United States
| | - Geoffrey Roest
- School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, Arizona 85287, United States
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Miller SM, Miller CE, Commane R, Chang RYW, Dinardo SJ, Henderson JM, Karion A, Lindaas J, Melton JR, Miller JB, Sweeney C, Wofsy SC, Michalak AM. A multi-year estimate of methane fluxes in Alaska from CARVE atmospheric observations. GLOBAL BIOGEOCHEMICAL CYCLES 2016; 30:1441-1453. [PMID: 28066129 PMCID: PMC5207046 DOI: 10.1002/2016gb005419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Methane (CH4) fluxes from Alaska and other arctic regions may be sensitive to thawing permafrost and future climate change, but estimates of both current and future fluxes from the region are uncertain. This study estimates CH4 fluxes across Alaska for 2012-2014 using aircraft observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) and a geostatistical inverse model (GIM). We find that a simple flux model based on a daily soil temperature map and a static map of wetland extent reproduces the atmospheric CH4 observations at the state-wide, multi-year scale more effectively than global-scale, state-of-the-art process-based models. This result points to a simple and effective way of representing CH4 flux patterns across Alaska. It further suggests that contemporary process-based models can improve their representation of key processes that control fluxes at regional scales, and that more complex processes included in these models cannot be evaluated given the information content of available atmospheric CH4 observations. In addition, we find that CH4 emissions from the North Slope of Alaska account for 24% of the total statewide flux of 1.74 ± 0.44 Tg CH4 (for May-Oct.). Contemporary global-scale process models only attribute an average of 3% of the total flux to this region. This mismatch occurs for two reasons: process models likely underestimate wetland area in regions without visible surface water, and these models prematurely shut down CH4 fluxes at soil temperatures near 0°C. As a consequence, wetlands covered by vegetation and wetlands with persistently cold soils could be larger contributors to natural CH4 fluxes than in process estimates. Lastly, we find that the seasonality of CH4 fluxes varied during 2012-2014, but that total emissions did not differ significantly among years, despite substantial differences in soil temperature and precipitation; year-to-year variability in these environmental conditions did not affect obvious changes in total CH4 fluxes from the state.
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Affiliation(s)
- Scot M. Miller
- Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA
| | - Charles E. Miller
- Science Division, NASA Jet Propulsion Laboratory, Pasadena, California, USA
| | - Roisin Commane
- School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Rachel Y.-W. Chang
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Steven J. Dinardo
- Science Division, NASA Jet Propulsion Laboratory, Pasadena, California, USA
| | | | - Anna Karion
- National Institute of Standards and Technology, Gaithersburg, Maryland, USA
| | - Jakob Lindaas
- Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
| | - Joe R. Melton
- Climate Research Division, Environment and Climate Change Canada, Victoria, Canada
| | | | - Colm Sweeney
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
| | - Steven C. Wofsy
- School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Anna M. Michalak
- Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA
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