CO_2 Transport, Variability, and Budget over the Southern California Air Basin Using the High-Resolution WRF-VPRM Model during the CalNex 2010 Campaign

Abstract

To study regional-scale carbon dioxide (CO_2) 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 CO_2 emissions of the Hestia Project 2010 fossil-fuel CO_2 emissions data products along with optimized VPRM parameters at “FLUXNET” sites, for biospheric CO_2 fluxes over SoCAB. The simulated meteorological conditions have been validated with ground and aircraft observations, as well as with background CO_2 concentrations from the coastal Palos Verdes site. The model captures the temporal pattern of CO_2 concentrations at the ground site at the California Institute of Technology in Pasadena, but it overestimates the magnitude in early daytime. Analysis of CO_2 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 CO_2 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 CO_2 budget. The total biospheric contribution ranges approximately from −24% to −20% (daytime) of the total anthropogenic CO_2 emissions during the study period.