HR: 0800h
AN: B51C-0211    [Abstracts]
TI: Where do Fossil Fuel Carbon Dioxide Emissions from the Western U.S. Go? An Analysis Based on an Atmospheric Model Validated Using Radiocarbon Observations (A Component of NACP-W)
AU: * Riley, W J
EM: wjriley@lbl.gov
AF: Lawrence Berkeley National Lab, Earth Sciences Division, 90-1106, 1 Cyclotron Rd, Berkeley, CA 94720 United States
AU: Hsueh, D
EM: dhsueh@uci.edu
AF: U.C. Irvine, Earth System Science Department 3212 Croul Hall University of California, Irvine, CA 92697-3100 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: U.C. Irvine, Earth System Science Department 3212 Croul Hall University of California, Irvine, CA 92697-3100 United States
AU: Fischer, M L
EM: mlfischer@lbl.gov
AF: Lawrence Berkeley National Lab, EETD, 51-0208A, 1 Cyclotron Rd, Berkeley, CA 94720
AU: Hatch, J
EM: joshuahatch@gmail.com
AF: Lawrence Berkeley National Lab, EETD, 51-0208A, 1 Cyclotron Rd, Berkeley, CA 94720
AB: We describe a combined measurement and modeling approach to assess the fate of fossil fuel CO₂ emissions released within California. In our analysis, we compared the ¹⁴C content of California annual C₃ grasses with spatially and temporally resolved fossil fuel CO₂ concentration estimates obtained using the MM5 atmospheric model and emissions inventories. Annual grasses sampled at the end of the growing season represent a weighted (with photosynthetic uptake) growing season atmospheric CO₂ sample. Their ¹⁴C content can be used to infer the fraction of assimilated carbon associated with fossil fuel since these CO₂ emissions are completely depleted in ¹⁴C. We sampled grasses at about 100 sites distributed throughout California, with special foci in the Central Valley, Los Angeles, and San Francisco air basins. Grass ¹⁴C content ranged from ~10 to ~60‰ in densely and sparsely populated areas, respectively. To analyze these ¹⁴C data, we applied a model that couples meteorological transport, ecosystem CO₂ exchange, and fossil fuel CO₂ emissions. The patterns of annual grass ¹⁴C content are consistent with our estimated fossil fuel CO₂ emissions and predicted atmospheric transport. We then applied the coupled model to assess fossil fuel CO₂ transport pathways out of the region. Accumulated over the year, about half of the fossil fuel CO₂ emitted in California exits to the south within the atmospheric boundary layer (ABL) while most of the remaining CO₂ exits in a disperse and lofted plume to the east. These results suggest that atmospheric sampling programs designed to enable continental `top down' inversions of North American sources and sinks should include an accurate assessment of north to south flow components, transport within the ABL, and exchange between the ABL and free troposphere.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0430 Computational methods and data processing
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0466 Modeling
SC: Biogeosciences [B]
MN: Fall Meeting 2005