Development of an Implementation Plan for Atmospheric Carbon Monitoring in California

This report describes the design of atmospheric CO₂ concentration measurements that, in combination with other measurements and models, would be used to quantify regionally distributed CO₂ exchanges from California's terrestrial ecosystems and CO₂ emissions from fossil fuel combustion. Using models of net ecosystem CO₂ exchange (NEE), fossil fuel CO₂ emissions, and regional meteorology, we predict CO₂ concentration "signals" in the atmosphere. The predictions of NEE exhibit spatial and temporal variations that are controlled by land cover and climate. Fossil fuel CO₂ emissions from metropolitan areas are the strongest localized sources of CO₂ while weaker but spatially extensive fossil emissions are present throughout the Central Valley. We subdivide the CO₂ sources into four components: NEE inside and outside CA, and fossil fuel CO₂ inside and outside CA. Maps of predicted atmospheric CO₂ concentration signals from these four sources largely mirror the instantaneous emissions near strong sources but plumes of CO₂ enriched or depleted air are predicted to advect far from their sources. We then identify a baseline set of observing stations from existing and possible future sites that could be used to characterize in-state and out-of-state ecosystem and fossil fuel contributions to atmospheric CO₂ concentrations. For each of the stations we calculate mean midday concentration signals with standard deviation for each month and source. We also calculate the covariance of the signal due to NEE inside CA with each of the other signals to quantify how much of the signal from NEE inside CA might be readily separable from the other signals. On the basis of these predictions, we identify new observing stations and a measurement protocol that, in combination with existing stations, would provide data to estimate NEE within CA. Although beyond the scope of this project, future work should estimate the uncertainties in estimating California's NEE that would be obtained using atmospheric concentration data from the stations identified herein.