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Abstract:
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 Quality and Climate
Change (CalNex) 2010 campaign period, a model that couples the Weather Research and Forecasting (WRF)
Model with the Vegetation Photosynthesis and Respiration Model (VPRM) has been used. Our numerical
simulations use anthropogenic CO2 emissions of the Hestia Project 2010 fossil-fuel CO2 emissions data
products along with optimized VPRM parameters at ‘‘FLUXNET’’ sites, for biospheric CO2 fluxes over
SoCAB. The simulated meteorological conditions have been validated with ground and aircraft observations,
as well as with background CO2 concentrations from the coastal Palos Verdes site. The model captures the
temporal pattern of CO2 concentrations at the ground site at the California Institute of Technology in
Pasadena, but it overestimates the magnitude in early daytime. Analysis ofCO2 by wind directions reveals the
overestimate is due to advection from the south and southwest, where downtown Los Angeles is located. The
model also captures the vertical profile of CO2 concentrations along with the flight tracks. The optimized
VPRM parameters have significantly improved simulated net ecosystem exchange at each vegetation-class
site and thus the regional CO2 budget. The total biospheric contribution ranges approximately from 224%
to 220% (daytime) of the total anthropogenic CO2 emissions during the study period.
