. We estimate the overall CO2 , CH4 , and CO
flux from the South Coast Air Basin using an inversion that couples Total
Carbon Column Observing Network (TCCON) and Orbiting Carbon Observatory-2
(OCO-2) observations, with the Hybrid Single Particle Lagrangian Integrated
Trajectory (HYSPLIT) model and the Open-source Data Inventory for
Anthropogenic CO2 (ODIAC). Using TCCON data we estimate the direct
net CO2 flux from the SoCAB to be
104  ±  26 Tg  CO2  yr −1 for the study period of
July 2013–August 2016. We obtain a slightly higher estimate of
120  ±  30 Tg  CO2  yr −1 using OCO-2 data. These
 CO2 emission estimates are on the low end of previous work. Our net
 CH4 (360  ±  90 Gg  CH4  yr −1 ) flux estimate is
in agreement with central values from previous top-down studies going back to
2010 (342–440 Gg  CH4  yr −1 ). CO emissions are estimated at
487  ±  122 Gg CO yr −1 , much lower than previous top-down
estimates (1440 Gg CO yr −1 ). Given the decreasing emissions of CO,
this finding is not unexpected. We perform sensitivity tests to estimate how
much errors in the prior, errors in the covariance, different inversion
schemes, or a coarser dynamical model influence the emission estimates.
Overall, the uncertainty is estimated to be 25 %, with the largest
contribution from the dynamical model. Lessons learned here may help in
future inversions of satellite data over urban areas.

https://acp.copernicus.org/articles/18/16271/2018/acp-18-16271-2018.pdf

Southern California megacity CO 2 , CH 4 , and CO flux estimates using ground- and space-based remote sensing and a Lagrangian model

Measurements of Δ14C and CO2 can cleanly separate biogenic and fossil contributions to CO2 enhancements above background. Our measurements of these tracers in air around Los Angeles in 2015 reveal high values of fossil CO2 and a significant and seasonally varying contribution of CO2 from the urban biosphere. The biogenic CO2 is composed of sources such as biofuel combustion and human metabolism and an urban biospheric component likely originating from urban vegetation, including turf and trees. The urban biospheric component is a source in winter and a sink in summer, with an estimated amplitude of 4.3 parts per million (ppm), equivalent to 33% of the observed annual mean fossil fuel contribution of 13 ppm. While the timing of the net carbon sink is out of phase with wintertime rainfall and the sink seasonality of Southern California Mediterranean ecosystems (which show maximum uptake in spring), it is in phase with the seasonal cycle of urban water usage, suggesting that irrigated urban vegetation drives the biospheric signal we observe. Although 2015 was very dry, the biospheric seasonality we observe is similar to the 2006-2015 mean derived from an independent Δ14C record in the Los Angeles area, indicating that 2015 biospheric exchange was not highly anomalous. The presence of a large and seasonally varying biospheric signal even in the relatively dry climate of Los Angeles implies that atmospheric estimates of fossil fuel-CO2 emissions in other, potentially wetter, urban areas will be biased in the absence of reliable methods to separate fossil and biogenic CO2.

Large and seasonally varying biospheric CO2 fluxes in the Los Angeles megacity revealed by atmospheric radiocarbon

High resolution fossil fuel combustion CO 2 emission fluxes for the United States Kevin R. Gurney 1 , Daniel L. Mendoza 1 , Yuyu Zhou 1 , Marc L. Fischer 2 , Chris C. Miller 1 , Sarath Geethakumar 1 , Stephane de la Rue du Can 2 Department of Earth and Atmospheric Sciences/Department of Agronomy, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907; 2 Atmospheric Science Department, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, 90K-125, Berkeley, CA 94720 Corresponding Author: Kevin Robert Gurney Department of Earth and Atmospheric Sciences/Department of Agronomy, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907

High resolution fossil fuel combustion CO2 emission fluxes for theUnited States

Responses to COVID-19 have resulted in unintended reductions of city-scale carbon dioxide (CO2) emissions. Here, we detect and estimate decreases in CO2 emissions in Los Angeles and Washington DC/Baltimore during March and April 2020. We present three lines of evidence using methods that have increasing model dependency, including an inverse model to estimate relative emissions changes in 2020 compared to 2018 and 2019. The March decrease (25%) in Washington DC/Baltimore is largely supported by a drop in natural gas consumption associated with a warm spring whereas the decrease in April (33%) correlates with changes in gasoline fuel sales. In contrast, only a fraction of the March (17%) and April (34%) reduction in Los Angeles is explained by traffic declines. Methods and measurements used herein highlight the advantages of atmospheric CO2 observations for providing timely insights into rapidly changing emissions patterns that can empower cities to course-correct CO2 reduction activities efficiently.

/pdf/the-impact-of-covid-19-on-co2-emissions-in-the-los-angeles-4sdtix1afv.pdf

The Impact of COVID-19 on CO2 Emissions in the Los Angeles and Washington DC/Baltimore Metropolitan Areas

Ecosystem function (particularly CO2 fluxes and the subsequent atmospheric transport), synoptic‐scale weather (e.g., midlatitude cyclones), and interactions between ecosystems and the atmosphere can be investigated using a weather‐biosphere‐online‐coupled model. The Vegetation Photosynthesis and Respiration Model (VPRM) was coupled with the Weather Research and Forecasting (WRF) model in 2008 to simulate “weather‐aware” biospheric CO2 fluxes and subsequent transport and dispersion. The ability of the coupled WRF‐VPRM modeling system to simulate the CO2 structures within midlatitude cyclones, however, has not been evaluated due to the lack of data within these weather systems. In this study, VPRM parameters previously calibrated off‐line using eddy covariance tower data over North America are implemented into WRF‐VPRM. The updated WRF‐VPRM is then used to simulate spatiotemporal variations of CO2 over the contiguous United States at a horizontal grid spacing of 12 km for 2016 using an optimized downscaling configuration. The downscaled fields are evaluated using remotely sensed data from the Orbiting Carbon Observatory‐2, Total Carbon Column Observing Network, and in situ aircraft measurements from Atmospheric Carbon and Transport‐America missions. Evaluations show that WRF‐VPRM captures the monthly variation of column‐averaged CO2 concentrations (XCO2) and episodic variations associated with frontal passages. The downscaling also successfully captures the horizontal CO2 gradients across fronts and vertical CO2 contrast between the boundary layer and the free troposphere. WRF‐VPRM modeling results indicate that from May to September, biogenic fluxes dominate variability in XCO2 over most of the contiguous United States, except over a few metropolitan areas such as Los Angeles. Plain Language Summary Global warming due to increase in greenhouse gases, particularly CO2, is well known as a critical issue facing humanity. CO2 concentration increased quickly over the past two centuries, with the overall trend largely due to fossil fuel emissions. Year‐to‐year variations in CO2 growth rate are not well understood, which is partially due to uncertainty in terrestrial CO2 fluxes. Accurate estimation of terrestrial CO2 fluxes is limited by land cover and land use changes, drought, and weather influences. These factors/processes and their impact on CO2 fluxes and atmospheric mole fractions can be investigated using a weather‐biosphere‐online‐coupled model. The Vegetation Photosynthesis and Respiration Model (VPRM) coupled with the Weather Research and Forecasting (WRF) model (referred to as WRF‐VPRM) is one such tool. In this study, optimal VPRM parameters are implemented into WRF‐VPRM. The updated WRF‐VPRM is then used to simulate CO2 mole fractions over the United States for 2016. The simulation is evaluated using aircraft measurements and remote sensing data. Evaluations show that WRF‐VPRM captures the temporal variation of CO2 concentrations, as well as the horizontal CO2 gradients across fronts and vertical CO2 contrast in the low troposphere. Simulations using this modeling system can be used to help understand regional to global CO2 budgets. © 2020. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. RESEARCH ARTICLE 10.1029/2019MS001875 Special Section: Carbon and Weather: Results from the Atmospheric Carbon and Transport ‐‐ America Mission Key Points: • The simulation is evaluated using CONUS‐scale, long‐term data, and in situ measurements that resolve the structures of midlatitude cyclones • WRF‐VPRM is shown to reproduce the structures in CO2 mole fractions observed within midlatitude cyclones • From May to September, biogenic fluxes dominate variability in XCO2 over most of the CONUS except around a few metropolitan areas such as LA Supporting Information: • Supporting Information S1 Correspondence to: X.‐M. Hu, xhu@ou.edu Citation: Hu, X.‐M., Crowell, S., Wang, Q., Zhang, Y., Davis, K. J., Xue, M., et al. (2020). Dynamical Downscaling of CO2 in 2016 Over the Contiguous United States Using WRF‐VPRM, a Weather‐Biosphere‐Online‐Coupled Model. Journal of Advances in Modeling Earth Systems, 12, e2019MS001875. https://doi.org/10.1029/2019MS001875 Received 20 AUG 2019 Accepted 4 MAR 2020 Accepted article online 11 MAR 2020

Dynamical Downscaling of CO2 in 2016 Over the Contiguous United States Using WRF-VPRM, a Weather-Biosphere-Online-Coupled Model

To study regional-scale carbon dioxide (CO2) transport, temporal variability, and budget over the Southern California Air Basin (SoCAB) during the California Research at the Nexus of Air Qu...

/pdf/co2-transport-variability-and-budget-over-the-southern-4wls5j25ik.pdf

Soon Young Park

Papers

CO2 Transport, Variability, and Budget over the Southern California Air Basin Using the High-Resolution WRF-VPRM Model during the CalNex 2010 Campaign