Consistent weekly cycles of atmospheric NO₂, CO, and CO₂ in a North American megacity from ground-based, mountaintop, and satellite measurements
Abstract
The weekday-weekend effect of anthropogenic emissions in cities, driven by the associated weekly changes in human activities, provides a unique opportunity to assess the sensitivity of observation networks (e.g., ground-based and space-borne instruments) on urban emissions. In this study, we focus on the weekly cycle amplitudes of nitrogen dioxide (NO₂), carbon monoxide (CO), and carbon dioxide (CO₂) in the Los Angeles (LA) megacity, where a significant weekly cycle of human activities exists. In addition, abundant observations are being produced continuously from existing ground-based, mountaintop, and satellite platforms to monitor carbon emissions and air quality in LA. From our analysis, significant agreement can be found in observations from different platforms. For NO₂, a 30%–35% Sunday decline relative to mid-week mixing ratios can be observed from both ground-based and satellite observations. For CO, the Sunday drops from ground-based, mountain-top and satellite observations are 13%–20%. The TROPOMI instrument with its high spatial resolution provides detailed spatial information on the reduction of tropospheric NO₂ and CO columns on Sundays. The spatial pattern is in good agreement with traffic density in LA. Impact due to the prevailing winds from the coast in the afternoon can also be observed. For anthropogenic CO₂, we show that the weekly cycle of XCO₂ enhancement above background from OCO-2 observations has a Sunday decline (15%–20%) consistent with ground-based observations and TCCON. This weekly pattern of CO₂ in a megacity directly detected by OCO-2 is reported for the first time. In addition, we also investigate the weekly cycles in the stable carbon isotopic composition of CO₂ (δ¹³C) from ground-based observations, which demonstrates the weekly variation in fossil fuel usage in LA. Finally, using the COVID-19 lockdown period as an example of a short-term perturbation on anthropogenic emissions, we found that the weekly cycle amplitude became larger during the lockdown period primarily because of the traffic volume changes in light-duty vehicles. This study highlights the consistencies and effectiveness of existing observing platforms in monitoring the anthropogenic emissions of the LA megacity.
Additional Information
© 2021 Elsevier. Received 31 May 2021, Revised 10 October 2021, Accepted 20 October 2021, Available online 27 October 2021, Version of Record 2 November 2021. We thank the California Air Resource Board for providing the ground-based NO₂ observations, available at https://www.arb.ca.gov/aqmis2/aqdselect.php, the LA Megacities Carbon Project for providing the ground-based CO and CO₂ observations, available at https://megacities.jpl.nasa.gov/public/Los_Angeles/In_Situ/ and https://data.nist.gov/od/id/mds2-2388, the Total Carbon Column Observing Network for providing the CO and CO₂ data at https://tccondata.org/, and the CO observations from CLARS that are available at https://megacities.jpl.nasa.gov/public/ and https://data.caltech.edu/records/1985. The tropospheric columns of NO₂ and CO from TROPOMI were downloaded from Google Earth Engine (https://earthengine.google.com/). The CO2 observations from OCO-2 are publicly available at https://disc.gsfc.nasa.gov/datasets/OCO2_L2_Lite_FP_9r/summary. The wind speed and direction were downloaded from TCCON weather station on Caltech campus (http://tccon-weather.caltech.edu/). The observations of mixing layer depth are available at http://megacities.jpl.nasa.gov/portal/. The traffic counts were download from PEMS (pems.dot.ca.gov). The ODIAC high-spatial resolution global emission data product of CO₂ emissions from fossil fuel combustion is available at https://db.cger.nies.go.jp/dataset/ODIAC/. The vehicle miles travelled (VMT) are downloaded from the Caltrans Performance Measurement System (PEMS: pems.dot.ca.gov). The data collected by the Megacities Carbon Network was partially funded by NIST's Greenhouse Gas Measurements Program. Support for Earth Networks was provided by NIST grants 70NANB15H344, 70NANB14H322, and NIST commercial contract 1333ND19PNB600853. Support to JPL for Network management and oversight was provided via an interagency agreement between NIST and NASA. A portion of this Megacities Carbon Network research was carried out at JPL, California Institute of Technology, under a contract with NASA (80NM0018D0004). CRediT authorship contribution statement. Huidong Wang: Data curation, Methodology, Investigation, Software, Writing – original draft. Fang-Ying Gong: Visualization, Investigation, Writing – review & editing. Sally Newman: Validation, Writing – review & editing. Zhao-Cheng Zeng: Conceptualization, Methodology, Writing – review & editing, Supervision. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Additional details
- Alternative title
- Consistent weekly cycles of atmospheric NO2, CO, and CO2 in a North American megacity from ground-based, mountaintop, and satellite measurements
- Eprint ID
- 114746
- Resolver ID
- CaltechAUTHORS:20220513-557957000
- 70NANB15H344
- National Institute of Standards and Technology (NIST)
- 70NANB14H322
- National Institute of Standards and Technology (NIST)
- 1333ND19PNB600853
- National Institute of Standards and Technology (NIST)
- 80NM0018D0004
- NASA/JPL/Caltech
- Created
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2022-05-13Created from EPrint's datestamp field
- Updated
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2022-05-13Created from EPrint's last_modified field