Identification of Anthropogenic CO2Using Triple Oxygen and Clumped Isotopes.
Quantification of contributions from various sources of CO2is important for understanding the atmospheric CO2budget. Considering the number and diversity of sources and sinks, the widely used proxies such as concentration and conventional isotopic compositions (δ13C and δ18O) are not always sufficient to fully constrain the CO2budget. Additional constraints may help in understanding the mechanisms of CO2production and consumption. The anomaly in triple oxygen isotopes or17O excess (denoted by Δ17O) and molecules containing two rare isotopes, called clumped isotopes, are two recently developed tracers with potentials to independently constrain some important processes that regulate CO2in the atmosphere. The clumped isotope for CO2, denoted by Δ47, is the excess of13C16O18O over a random distribution of isotopes in a CO2molecule. We measured the concentrations of δ13C, δ18O, Δ17O, and Δ47in air CO2samples collected from the Hsuehshan tunnel (length: 12.9 km), and applied linear and polynomial regressions to obtain the fossil fuel end-members for all these isotope proxies. The other end-members, the values of all these proxies for background air CO2, are either assumed or taken as the values obtained over the tunnel and ocean. The fossil fuel (anthropogenic) CO2end-member values for δ13C, δ18O, Δ17O, and Δ47are estimated using the two component mixing approach: the derived values are -26.76 ± 0.25‰, 24.57 ± 0.33‰, -0.219 ± 0.021‰, and 0.267 ± 0.036‰, respectively. These four major CO2isotope tracers along with the concentration were used to estimate the anthropogenic contribution in the atmospheric CO2in urban and suburban locations. We demonstrate that Δ17O and Δ47have the potential to independently estimate anthropogenic contribution, and the advantages of these two over the conventional isotope proxies are discussed.
Research Center for Environmental Changes , Academia Sinica, Taipei 11529, Taiwan.
Amzad H
AH
Laskar
Research Center for Environmental Changes , Academia Sinica, Taipei 11529, Taiwan.
Sasadhar
S
Mahata
Research Center for Environmental Changes , Academia Sinica, Taipei 11529, Taiwan.|Graduate Institute of Astronomy, National Central University , Taoyuan City 32001, Taiwan.|Department of Physics, University of Houston , Houston, Texas 77204, United States.
Mao-Chang
MC
Liang
D001272:Atmosphere; D002247:Carbon Isotopes; D005579:Fossil Fuels; D010100:Oxygen; D010103:Oxygen Isotopes
D002247:Carbon Isotopes; D005579:Fossil Fuels; D010103:Oxygen Isotopes; D010100:Oxygen