Data from: The radiocarbon composition of tree rings as a tracer of local fossil fuel emissions in the Los Angeles basin: 1980–2008

Quantifying local fossil fuel CO2 emissions in urban areas is challenging
due to the heterogeneity in emissions and in atmospheric mixing ratios of
CO2. Measurements of the radiocarbon content of urban tree rings are an
alternative to large networks of CO2monitoring stations. In this study, we
calculated 3-year averages of CO2 mixing ratios from fossil fuel
combustion from 1980 to 2008 using tree rings sampled at six sites within
the Los Angeles basin and adjacent mountains. We observed CO2 mixing
ratios from fossil fuel combustion of up to 23 μmol·mol−1 in the inland
basin and ∼5–10 μmol·mol−1at coastal sites. Although we expected to see
increasing trends of fossil fuel-derived CO2over time, not all sites
showed a significant increase. Analysis of correlations between fossil
fuel-derived CO2and socioeconomic variables revealed that fossil
fuel-derived CO2 followed trends in census tract and/or city population or
in vehicle statistics at most sites. We also calculated CO/CO2combustion
ratios from tree ring radiocarbon and nearby measurements of atmospheric
CO mixing ratios. We observed widespread declines in the combustion ratio
that support increases in the efficiency of the automobile fleet over the
past few decades. This study demonstrates the utility of tree ring
radiocarbon measurements for quantifying temporal and spatial patterns in
fossil fuel-derived CO2 emissions in urban areas.