CO₂ transport, variability, and budget over the Southern California Air Basin using the high-resolution WRF-VPRM model during the CalNex 2010 campaign

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 of CO₂ 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 -24% to -20% (daytime) of the total anthropogenic CO₂ emissions during the study period.