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

Data files

Oct 06, 2025 version files 488.22 KB

em27_xco2_fivemin.csv

259.93 KB
plant_14C.csv

12.85 KB
README.md

9.55 KB
surface_CO2_1hour_BEA_SMM_RIV.csv

205.89 KB

Abstract

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 cavity ringdown spectrometers, and XCO₂ was measured using a portable Fourier Transform solar spectrometer. Our data shows that plant ¹⁴C is highly sensitive to local ffCO₂ emissions at the intra-city scale and captures pronounced differences between urban to rural sites. We observe significant correlations between fossil fuel enhancements (C_ff) derived from plant ¹⁴C and from atmospheric CO₂. Our findings indicate that plant ¹⁴C analysis can be a very useful tool for quantifying ffCO₂ trends in cities that lack surface CO₂ and XCO₂ measurement infrastructure.

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
DLA	Los Angeles	University of Southern California	Yes	Yes	No. Publicly available from NIST at https://data.nist.gov/od/id/mds2-2388
PAS	Pasadena	California Institute of Technology	Yes	Yes	No. Publicly available from NIST at https://data.nist.gov/od/id/mds2-2388
IRV	Irvine	University of California, Irvine	Yes	Yes	no. Publicly available from NIST at https://data.nist.gov/od/id/mds2-2388
RIV	Riverside	University of California, Riverside	Yes	Yes	Yes
BEA	Beaumont	Noble Creek Regional Park	Yes	Yes	Yes
SMM	Calabasas	Stunt Ranch, Santa Monica Mountains	One annual grass in Aug 2022	Yes, but only visited on two days (Aug 8, 2022 and Nov 14, 2022)	yes
MWO	Mount Wilson	Mount Wilson Observatory	One annual grass in Aug 2022	Yes, only visited on one day (Aug 8, 2022)	n/a

We aimed to visit DLA, PAS, IRV, RIV, and BEA twice per seasonal measurement campaign if the weather permitted XCO2 measurements (little to no cloud cover). MWO and SMM are secondary sites and were only visited occasionally to evaluate local background conditions.

To calculate fossil fuel CO2 enhancements, our study also relied on measurements collected in "background" sites to represent clean, ambient conditions prior to the enhancement caused by fossil fuel CO2 emissions. The background sites are either upwind of the urban area or in remote locations assumed to have minimal influence from fossil sources. The background data were provided by other publicly accessible datasets and so are not in this repository.

Background for surface CO2 provided by the Los Angeles Megacity Carbon Project (https://data.nist.gov/od/id/mds2-2388) (Kim et al., 2024; Verhulst et al., 2017)
- San Clemente Island (SCI)
- Victorville (VIC)
Background XCO2 provided by the TCCON (https://tccondata.org/) (Wunch et al., 2009)
- Edwards (AFRC)
Background Air 14C (Xu, pers. comm. 2023)
- Utqiagvik, AK (PTB)

Description of the data and file structure

This dataset includes three sets of measurements, each in their own .csv file:

plant_14C.csv - Plant radiocarbon data
surface_CO2_1hour_BEA_SMM_RIV.csv - 1 hour averages of surface CO2 measured at BEA, SMM, and RIV sites
em27_xco2_fivemin.csv - five-minute averages of XCO2 at DLA, PAS, IRV, RIV, BEA, SMM, and MWO

Further details about each file are described below.

Plant 14C (plant_14C.csv)

This file includes radiocarbon data from 147 plant samples collected at the sites listed above. The columns included are:

UCIT: lab sample identification number
site: three letter site ID defined in the table above
collection_date: the date the sample was collected
year: year of collection
month: month of collection
description: describes location of plant sample relative to where the EM27 was stationed in the format "campus_season_distance-from-EM27-in-meters_direction-from-EM27"
latitude: coordinates in degrees north
longitude: coordinates in degrees east
season: seasonal campaign when sample was collected (Spring 2022, Summer 2022, Fall 2022, Winter 2023)
D14C_obs: measured 14C content of the sample, in the ∆14C notation. The units are in per mil (‰). The ∆14C notation represents the absolute amount of radiocarbon at the time it was measured, including a correction for the radioactive decay of the standard. This notation was used for all analyses in the manuscript. 14C notations are described in detail in Trumbore et al. (2016)
D14C_obs_err: AMS measurement uncertainty of the 14C result in per mil units (‰)
D14C_bg_ptb: the estimated ∆14C (‰) background based on air 14CO2 measurements collected in Utqiagvik, AK (Xu, pers. comm., 2023). These air samples are collected in flasks over approximately one month. The values reported here are the average of the air samples collected in the month the plant samples were collected.

Surface CO2 (surface_CO2_1hour_BEA_SMM_RIV.csv)

This file includes the surface CO2 measurements collected at BEA, SMM, and RIV. The data has been aggregated to 1-hour resolution. BEA and SMM measurements were only collected during the site visit while RIV measurements were collected continuously on the roof of Winston Chung Hall at UC Riverside. All values have been calibrated against standard tanks with known CO2 moixing ratios. The columns included are:

timestamp_PTZ: time in Pacific time zone
site: three letter side ID defined in the table above
CO2: 1-hour averaged CO2 in ppm
CO2_sd: standard deviation of the 1-hour CO2 average in ppm

XCO2 (em27_xco2_fivemin.csv)

This file includes XCO2 measurements collected with the EM27/SUN. Column description:

timestamp_PTZ: time in Pacific time zone
lat(deg): latitude coordinates in degrees north
long(deg): longitude coordinates in degrees east
year
month
day
dayID: date identifier in format YYYYMMDD
season: measurement campaign code. (1 = Spring 2022; 2 = Summer 2022; 3 = Fall 2022; 4 = Winter 2023)
site: three letter side ID defined in the table above
xco2(ppm): total column CO2 in units of ppm, averaged into 5-minute bins
xco2(ppm)_error: measurement uncertainty in total column CO2

Further details about our methodology can be found in our manuscript titled "Plant radiocarbon across an urban-rural CO2 gradient matches surface and column CO2 observations," currently in review.

References

Kim, J., Verhulst, K., Lueker, T., Salameh, P., Cox, A., Walker, S., Paplawsky, W., Prinzivalli, S., Fain, C., Stock, M., DiGangi, E., Biggs, B., Angel, B., Karion, A., Pongetti, T., Callahan, W., Weiss, R., Keeling, R., & Miller, C. (2022). In Situ Carbon Dioxide, Methane, and Carbon Monoxide Mole Fractions from the Los Angeles Megacity Carbon Project, National Institute of Standards and Technology [dataset]. https://doi.org/10.18434/mds2-2388

Trumbore, S. E., Sierra, C. A., & Hicks Pries, C. E. (2016). Radiocarbon Nomenclature, Theory, Models, and Interpretation: Measuring Age, Determining Cycling Rates, and Tracing Source Pools. In E. A. G. Schuur, E. Druffel, & S. E. Trumbore (Eds.), Radiocarbon and Climate Change: Mechanisms, Applications and Laboratory Techniques (pp. 45–82). Springer International Publishing. https://doi.org/10.1007/978-3-319-25643-6_3

Verhulst, K. R., Karion, A., Kim, J., Salameh, P. K., Keeling, R. F., Newman, S., Miller, J., Sloop, C., Pongetti, T., Rao, P., Wong, C., Hopkins, F. M., Yadav, V., Weiss, R. F., Duren, R. M., & Miller, C. E. (2017). Carbon dioxide and methane measurements from the Los Angeles Megacity Carbon Project–Part 1: calibration, urban enhancements, and uncertainty estimates. Atmospheric and Climate Sciences. https://doi.org/10.5194/acp-17-8313-2017

Wunch, D., Wennberg, P. O., Toon, G. C., Keppel-Aleks, G., & Yavin, Y. G. (2009). Emissions of greenhouse gases from a North American megacity. Geophysical Research Letters, 36(15). https://doi.org/10.1029/2009gl039825

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 Angeles, Pasadena, and Irvine was provided by the Los Angeles Megacities (LAM) Carbon Project, which is a network of rooftop or tower sites managed by the National Institute of Standards and Technology (NIST). The surface CO₂ data from the LAM network is publicly available at https://data.nist.gov/od/id/mds2-2388 (Verhulst et al., 2017; Kim et al., 2024). Surface CO₂ data collected in Riverside and Beaumont is not managed by NIST and is publicated here. At Beaumont, we measured surface CO₂ at a public park using a Picarro G2401 cavity ringdown spectrometer. Riverside surface CO₂ measurements were collected on a rooftop at the University of California, Riverside.

In addition to the five study sites along the urban-rural gradient, our analysis also relied on measurements at "background" sites. To estimate contributions from fossil fuel-derived CO₂ emissions, we used ¹⁴C, surface CO₂, and XCO₂ data at several sites to quantify the atmospheric background. For ¹⁴C, the background estimates were based on monthly-integrated air samples collected at Utqiagvik, AK, a remote location far from fossil fuel emission sources (Xu, pers. comm 2023). For surface CO₂, measurements at San Clemente Island and Victorville, CA were used to characterize the background (Verhulst et al., 2017; Kim et al., 2024). For XCO₂, measurements at the NASA Armstrong Flight Research Center, a remote desert site near Edwards, CA, were used to estimate background. This site is part of the TCCON network and the data is available at https://tccondata.org/.