Plant radiocarbon across an urban-rural CO2 gradient matches surface and column CO2 observations

Atmospheric measurements are needed to verify progress in reducing fossil fuel carbon dioxide (ffCO2) emissions, especially in cities where most ffCO2 is emitted. However, because of complexities in atmospheric dynamics and large natural CO2 fluxes, ambient CO2 measurements alone cannot distinguish ffCO2 signals. Analysis of the radiocarbon (14C) content of urban plants can reveal ffCO2 patterns and is more cost-effective than air 14CO2 sampling, but its use has been limited because of uncertainty in the temporal integration period and because it has not been quantitatively evaluated against other atmospheric monitoring approaches. We analyzed the 14C content of turfgrasses collected along an urban to rural gradient in Southern California. The primary study sites are Downtown Los Angeles, Pasadena, Irvine, Riverside, and Beaumont, CA. We compare these plant 14C to multiscale, atmospheric CO2 measurements including surface CO2 and total column CO2 (XCO2). Surface CO2 was measured using c..., Measurements of plant 14C, XCO2, and surface CO~2 ~were collected approximately every three months between May 2022 to March 2023. The study focused on five sites along an urban to rural gradient in the Greater Los Angeles area: Downtown Los Angeles, Pasadena, Irvine, Riverside, and Beaumont, CA. At each site, a series of turfgrass samples were collected on irrigated lawns, mostly on university campuses or public parks. A total of 147 plant samples were analyzed for 14C content at the University of California's Keck Carbon Cycle AMS facility.
We also collected ground-based XCO2 measurements using a portable Fourier Transform Spectrometer (\"EM27/SUN\", Bruker). XCO2 was measured at each site for two days per seasonal campaign during sunny conditions. The XCO2 data was calibrated based on side-by-side measurements with the Total Carbon Column Observing Network (TCCON) site at Caltech, Pasadena. TCCON data is publicly available at https://tccondata.org/.
Surface CO2 data for Downtown Los An..., , # Data from: Plant radiocarbon across an urban-rural CO2 gradient matches surface and column CO2 observations

[https://doi.org/10.5061/dryad.wstqjq2vd](https://doi.org/10.5061/dryad.wstqjq2vd)

This dataset includes measurements of plant 14C, surface CO2, and total column CO2 (XCO2), which were collected approximately every three months between May 2022 to March 2023 along an urban to rural gradient in Southern California. The study sites are listed below in order from highest to lowest population density (urban to rural). Unless otherwise stated on the table below, all plant samples were turf grasses.

| Site ID | City | Location | Plant 14C data included | XCO2 data included | Surface CO2 data included |
| :------ | :----------- | :---------------------------------- | :--------------------------- | :------------...,