@article{bibcite_36608,
  author = {Matthew S Johnson and Sofia D Hamilton and Seongeun Jeong and Yu Yan Cui and Dien Wu and Alex Turner and Marc L Fischer},
  title = {State-wide California 2020 carbon dioxide budget estimated with OCO-2 and OCO-3 satellite data},
  abstract = {<p>Abstract. Satellite observations are instrumental in observing spatiotemporal variability in carbon dioxide (CO2) concentrations, which can be used to derive fluxes of this greenhouse gas. This study leverages NASA{\textquoteright}s Orbiting Carbon Observatory-2 and -3 (OCO-2 and OCO-3, respectively) CO2 observations with a Gaussian process (GP) machine learning inverse model, a Bayesian nonparametric approach well suited for integrating the unique spatiotemporal characteristics of these satellite observations, to estimate subregional CO2 fluxes. Utilizing the GEOS-Chem chemical transport model (CTM) to simulate column-average CO2 concentrations (XCO2) for 2020 in California {\textendash} a period marked by the coronavirus disease (COVID-19) pandemic, drought conditions, and significant wildfire activity {\textendash} we estimated the state-wide CO2 emission rates constrained by OCO-2/3. This study developed prior fossil fuel emissions to reflect reduced activities during the COVID-19 pandemic, while net ecosystem exchange (NEE) and fire emissions were derived based on satellite data. GEOS-Chem source-specific XCO2 concentrations for fossil fuels, NEE, fire, and oceanic sources were simulated coincident to OCO-2/3 XCO2 retrievals to estimate state-wide sector-specific and total CO2 emissions. GP inverse model results suggest that annual posterior median fossil fuel emissions were consistent with prior estimates (317.8 and 338.4 Tg CO2 yr-1, respectively; 95 \% confidence level) and that posterior NEE fluxes had less carbon uptake compared to prior fluxes (-36.8 vs. -99.2 Tg CO2 yr-1, respectively; 95 \% confidence level). Posterior fire CO2 emissions were estimated to be 68.0 Tg CO2 yr-1, which was much lower than a priori estimates (103.3 Tg CO2 yr-1). The total median annual CO2 emissions for the state of California in 2020 were estimated to be 349.6 Tg CO2 yr-1 (range of 272.8{\textendash}428.6 Tg CO2 yr-1; 95 \% confidence level), aligning closely with the prior total estimate of 342.5 Tg CO2 yr-1. This study, for the first time, demonstrates that OCO-2/3 XCO2 observations can be assimilated into inverse models to estimate state-wide source-specific CO2 fluxes on a seasonal and annual scale.
                    </p>},
  year = {2025},
  booktitle = {Atmospheric Chemistry and Physics},
  journal = {Atmospheric Chemistry and Physics},
  series = {Atmospheric Chemistry and Physics},
  volume = {25},
  pages = {8475-8492},
  month = {05/08/2025},
  institution = {Copernicus GmbH},
  publisher = {Copernicus GmbH},
  issn = {1680-7324},
  url = {https://doi.org/10.5194/acp-25-8475-2025},
  doi = {10.5194/acp-25-8475-2025},
}