Clumped isotopes in near-surface atmospheric CO.sub.2 over land, coast and ocean in Taiwan and its vicinity

• Published in: Biogeosciences 2016-09, Vol.13 (18), p.5297
• Main Authors: Laskar, Amzad Hussain, Liang, Mao-Chang
• Format: Article
• Language: English
• Subjects: Chemical properties; Thermodynamics
• ISSN: 1726-4170; 1726-4189

Molecules containing two rare isotopes (e.g., .sup.13 C.sup.18 O.sup.16 O in CO.sub.2 ), called clumped isotopes, in atmospheric CO.sub.2 are powerful tools to provide an alternative way to independently constrain the sources of CO.sub.2 in the atmosphere because of their unique physical and chemical properties. We presented clumped isotope data (Δ.sub.47) in near-surface atmospheric CO.sub.2 from urban, suburban, ocean, coast, high mountain ( ∼  3.2 km a.s.l.) and forest in Taiwan and its vicinity. The primary goal of the study was to use the unique Δ.sub.47 signature in atmospheric CO.sub.2 to show the extents of its deviations from thermodynamic equilibrium due to different processes such as photosynthesis, respiration and local anthropogenic emissions, which the commonly used tracers such as [delta].sup.13 C and [delta].sup.18 O cannot provide. We also explored the potential of Δ.sub.47 to identify/quantify the contribution of CO.sub.2 from various sources. Atmospheric CO.sub.2 over ocean was found to be in thermodynamic equilibrium with the surrounding surface sea water. Respired CO.sub.2 was also in close thermodynamic equilibrium at ambient air temperature. In contrast, photosynthetic activity result in significant deviation in Δ.sub.47 values from that expected thermodynamically. The disequilibrium could be a consequence of kinetic effects associated with the diffusion of CO.sub.2 in and out of the leaf stomata. We observed that [delta].sup.18 O and Δ.sub.47 do not vary similarly when photosynthesis was involved unlike simple water-CO.sub.2 exchange. Additionally we obtained Δ.sub.47 values of car exhaust CO.sub.2 that were significantly lower than the atmospheric CO.sub.2 but higher than that expected at the combustion temperature. In urban and suburban regions, the Δ.sub.47 values were found to be lower than the thermodynamic equilibrium values at the ambient temperature, suggesting contributions from local combustion emission.