CaltechAUTHORS
Published October 2020 | Version Published
Journal Article Metadata-only

Tracking the atmospheric pulse of a North American megacity from a mountaintop remote sensing observatory

Creators

  • 1. ROR icon University of California, Los Angeles
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon Jet Propulsion Lab
  • 4. ROR icon Bay Area Air Quality Management District
  • 5. ROR icon University of Southern California

Abstract

Atmospheric carbon monoxide (CO) is an effective tracer for monitoring atmospheric transport processes and for detecting pollution sources of anthropogenic origin. However, very few observation systems exist that are capable of providing measurements with high spatial and temporal resolution to identify hotspots for emission control purposes. Here we introduce a mountain-top remote sensing observatory, the California Laboratory for Atmospheric Remote Sensing (CLARS), for mapping the enhancement of CO column-averaged mixing ratio (XCO) over the Los Angeles (LA) megacity. Compared to conventional observation network, CLARS is unique in the following ways: (1) it mimics a geostationary satellite observatory for LA with approximately hourly- and kilometer-scale mapping capability; (2) the free tropospheric background atmosphere is simultaneously measured; and (3) the measurements are highly sensitive to anthropogenic emissions due to the long light path along the planetary boundary layer (PBL). The CO slant column density and XCO are retrieved from reflected sunlight measurements in the 2.3 μm CO band and the 1.27 μm oxygen (O2) band. Data filtering and corrections for aerosol scattering and geometric effects are then implemented to derive the XCO enhancement, which is the XCO excess in the PBL compared to the background value. In the LA megacity, the XCO enhancement shows a distinctive diurnal cycle primarily driven by changes in anthropogenic emissions and sea-breeze circulation. Such diurnal patterns can be reproduced by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The enhancement also shows a significant weekly cycle resulting from the weekly pattern in anthropogenic CO emissions. On average, the XCO enhancements on Sunday and Saturday are 16.1% and 4.4%, respectively, lower than weekday values. The weekly XCO enhancement patterns also show high correlation with traffic counts. A seasonal pattern of XCO enhancement with high (low) spatial contrast in summer (winter), resulting from changing sea-breeze circulation, can be observed. These diurnal, weekly, and seasonal patterns of XCO enhancement serve as tracers of the atmospheric pulse of the LA megacity. The CLARS observatory can serve as a testbed for future geostationary missions to track anthropogenic emissions in cities.

Copyright and License

© 2020 Elsevier Inc. All rights reserved.

Acknowledgement

We thank the reviewers and Drs. Nehzat Motallebi, Matthias Falk, and Abhilash Vijayan at California Air Resources Board for constructive comments and suggestions that helped improve the manuscript. Discussions with Yi Yin and Jiani Yang at Caltech, Dylan Jones at University of Toronto, and Paul O. Wennberg at Caltech are acknowledged. We thank Dr. Jochen Stutz and his staff for establishing and maintaining the AERONET Caltech site. We also thank Dr. Pavel Ionov and his staff for establishing and maintaining the AERONET El Segundo site. The CLARS project receives support from the California Air Resources Board. However, the results presented in this study do not necessarily present the views of the funding agency. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). The AERONET data for Caltech and El Segundo are available at https://aeronet.gsfc.nasa.gov/. The CO emission inventories are downloaded from EPA (available at https://www.epa.gov/air-emissions-inventories/national-emissions-inventory-nei). We would like to acknowledge high-performance computing support to Z.-C. Zeng (UCIT0004) from Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation. WRF-Chem is developed and distributed by NCAR (available at https://www2.acom.ucar.edu/wrf-chem). We thank the European Centre for Medium-Range Weather Forecasts (ECMWF) for providing the ERA5 reanalysis dataset, available at https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5. Z. C. Zeng would also like to dedicate this paper to his newborn daughter Judith Zeng.

Additional details

Funding

National Aeronautics and Space Administration
80NM0018D0004
California Air Resources Board
National Science Foundation

Dates

Available
2020-07-22
Version of record

Caltech Custom Metadata

Caltech groups
Division of Geological and Planetary Sciences (GPS)
Publication Status
Published