TY - JOUR
T1 - Emissions and topographic effects on column CO2 (XCO2) variations, with a focus on the Southern California Megacity
AU - Hedelius, Jacob K.
AU - Feng, Sha
AU - Roehl, Coleen M.
AU - Wunch, Debra
AU - Hillyard, Patrick W.
AU - Podolske, James R.
AU - Iraci, Laura T.
AU - Patarasuk, Risa
AU - Rao, Preeti
AU - O’Keeffe, Darragh
AU - Gurney, Kevin
AU - Lauvaux, Thomas
AU - Wennberg, Paul O.
N1 - Funding Information:
ASTER GDEM is a product of METI and NASA. We gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model (http://www.ready.noaa.gov) used in this publication. OCO-2 lite files were produced by the OCO-2 project at the Jet Propulsion Laboratory, California Institute of Technology, and obtained from the OCO-2 data archive maintained at the NASA Goddard Earth Science Data and Information Services Center. Nightlight products were obtained from the Earth Observation Group, NOAA National Geophysical Data Center and are based on Suomi NPP satellite observations (http://ngdc.noaa.gov/eog/viirs/). TCCON data are available from the CDIAC and will also be available through the Caltech library archive by 2018 [Iraci et al.,; Wennberg et al.,]. Model data are available upon request. We thank Chris O'Dell and the ACOS team for early access to the GOSAT-ACOS v7.3 data. We thank Camille Viatte, Eric Kort, and Kristal Verhulst for helpful discussions. The authors thank funding sources. This work is supported in part by the W. M. Keck Institute for Space Studies. The authors gratefully acknowledge TCCON funding from the NASA Carbon Cycle Science program (grant numbers NNX14AI60G and NNX17AE15G), and the Jet Propulsion Laboratory OCO-2 program (grant 1517180). Kevin R. Gurney thanks NIST grant 70NANB14H321. The authors also wish to thank the OCO-2 Science Team grant NNX15AI42G and NASA EVS ACT-America grant NNX15AG76G. The authors thank the referees for their comments. This paper is edited by A. Steiner and reviewed by two anonymous referees.
Publisher Copyright:
© 2017. American Geophysical Union. All Rights Reserved.
PY - 2017
Y1 - 2017
N2 - Within the California South Coast Air Basin (SoCAB), XCO2 varies significantly due to atmospheric dynamics and the nonuniform distribution of sources. XCO2 measurements within the basin have seasonal variation compared to the “background” due primarily to dynamics, or the origins of air masses coming into the basin. We observe basin-background differences that are in close agreement for three observing systems: Total Carbon Column Observing Network (TCCON) 2.3 ± 1.2 ppm, Orbiting Carbon Observatory-2 (OCO-2) 2.4 ± 1.5 ppm, and Greenhouse gases Observing Satellite 2.4 ± 1.6 ppm(errors are 1σ). We further observe persistent significant differences (~0.9 ppm) in XCO2 between two TCCON sites located only 9 km apart within the SoCAB. We estimate that 20% (± 1σ confidence interval (CI): 0%, 58%) of the variance is explained by a difference in elevation using a full physics and emissions model and 36% (± 1 σ CI: 10%, 101%) using a simple, fixed mixed layer model. This effect arises in the presence of a sharp gradient in any species (here we focus on CO2) between the mixed layer (ML) and free troposphere. Column differences between nearby locations arise when the change in elevation is greater than the change in ML height. This affects the fraction of atmosphere that is in the ML above each site. We show that such topographic effects produce significant variation in XCO2 across the SoCAB as well. Plain Language Summary Cities persistently have elevated carbon dioxide (CO2) levels as compared to surrounding regions. Within a city CO2 levels can also vary significantly at different locations for reasons such as more CO2 being emitted in some parts than others. Elevated column CO2 levels in the South Coast Air Basin (SoCAB) are in agreement for three observation systems (two satellite and one ground-based) systems and vary with regional wind patterns throughout the year. In Pasadena, California, within the SoCAB, a significant fraction (about 25%) of variation in the column-averaged CO2 can be explained by differences in surface altitude. This is important to understand so that all variations in column CO2 within an urban region are not mistakenly interpreted as being from CO2 surface fluxes.
AB - Within the California South Coast Air Basin (SoCAB), XCO2 varies significantly due to atmospheric dynamics and the nonuniform distribution of sources. XCO2 measurements within the basin have seasonal variation compared to the “background” due primarily to dynamics, or the origins of air masses coming into the basin. We observe basin-background differences that are in close agreement for three observing systems: Total Carbon Column Observing Network (TCCON) 2.3 ± 1.2 ppm, Orbiting Carbon Observatory-2 (OCO-2) 2.4 ± 1.5 ppm, and Greenhouse gases Observing Satellite 2.4 ± 1.6 ppm(errors are 1σ). We further observe persistent significant differences (~0.9 ppm) in XCO2 between two TCCON sites located only 9 km apart within the SoCAB. We estimate that 20% (± 1σ confidence interval (CI): 0%, 58%) of the variance is explained by a difference in elevation using a full physics and emissions model and 36% (± 1 σ CI: 10%, 101%) using a simple, fixed mixed layer model. This effect arises in the presence of a sharp gradient in any species (here we focus on CO2) between the mixed layer (ML) and free troposphere. Column differences between nearby locations arise when the change in elevation is greater than the change in ML height. This affects the fraction of atmosphere that is in the ML above each site. We show that such topographic effects produce significant variation in XCO2 across the SoCAB as well. Plain Language Summary Cities persistently have elevated carbon dioxide (CO2) levels as compared to surrounding regions. Within a city CO2 levels can also vary significantly at different locations for reasons such as more CO2 being emitted in some parts than others. Elevated column CO2 levels in the South Coast Air Basin (SoCAB) are in agreement for three observation systems (two satellite and one ground-based) systems and vary with regional wind patterns throughout the year. In Pasadena, California, within the SoCAB, a significant fraction (about 25%) of variation in the column-averaged CO2 can be explained by differences in surface altitude. This is important to understand so that all variations in column CO2 within an urban region are not mistakenly interpreted as being from CO2 surface fluxes.
UR - http://www.scopus.com/inward/record.url?scp=85022345898&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85022345898&partnerID=8YFLogxK
U2 - 10.1002/2017JD026455
DO - 10.1002/2017JD026455
M3 - Article
AN - SCOPUS:85022345898
SN - 0148-0227
VL - 122
SP - 7200
EP - 7215
JO - Journal of Geophysical Research Atmospheres
JF - Journal of Geophysical Research Atmospheres
IS - 13
ER -