Abstract
Abstract. Molecules containing two rare isotopes (e.g., 13C18O16O in CO2), called clumped isotopes, in atmospheric CO2 are powerful tools to provide an alternative way to independently constrain the sources of CO2 in the atmosphere because of their unique physical and chemical properties. We presented clumped isotope data (Δ47) in near-surface atmospheric CO2 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 Δ47 signature in atmospheric CO2 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 δ13C and δ18O cannot provide. We also explored the potential of Δ47 to identify/quantify the contribution of CO2 from various sources. Atmospheric CO2 over ocean was found to be in thermodynamic equilibrium with the surrounding surface sea water. Respired CO2 was also in close thermodynamic equilibrium at ambient air temperature. In contrast, photosynthetic activity result in significant deviation in Δ47 values from that expected thermodynamically. The disequilibrium could be a consequence of kinetic effects associated with the diffusion of CO2 in and out of the leaf stomata. We observed that δ18O and Δ47 do not vary similarly when photosynthesis was involved unlike simple water–CO2 exchange. Additionally we obtained Δ47 values of car exhaust CO2 that were significantly lower than the atmospheric CO2 but higher than that expected at the combustion temperature. In urban and suburban regions, the Δ47 values were found to be lower than the thermodynamic equilibrium values at the ambient temperature, suggesting contributions from local combustion emission.
Highlights
The lowest CO2 concentration [CO2] and highest δ13C and δ18O values were observed during late morning hours, while highest [CO2] and lowest δ13C and δ18O values were observed during nighttime and early morning before sunrise (Table 1 and Fig. 2a–c), indicating that respiration and photosynthesis played the major role in controlling the variations of the [CO2] and isotopic compositions
We presented a compilation of 47 analyses for car exhaust, greenhouse and air CO2 over a wide variety of interactions in tropical and subtropical regions including marine, coastal, urban, suburban, forest and high mountain environments
Urban, suburban and greenhouse air CO2 significantly deviate from the thermodynamic equilibrium values
Summary
The budget of atmospheric CO2 is widely studied using the temporal and spatial variations in concentration and conventional isotopic compositions (δ13C and δ18O) of CO2 (Francey and Tans, 1987; Francey et al, 1995; Yakir and Wang, 1996; Ciais et al, 1995a, b, 1997; Peylin et al, 1999; Cuntz et al, 2003; Drake et al, 2011; Welp et al, 2011; Affek and Yakir, 2014). δ13C is useful to differentiate the exchange of CO2 with the ocean and land biospheres. Δ13C is useful to differentiate the exchange of CO2 with the ocean and land biospheres. This is due to the fact that the photosynthetic discrimination against 13C during exchange with land plants is higher than that associated with the chemical dissolution of CO2 in the ocean (e.g., Tans et al, 1993; Ciais et al, 1995a; Francey et al, 1995; Ito, 2003; Bowling et al, 2014).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
