TITLE

Investigations of the photochemical isotope equilibrium between O2, CO2 and O3

AUTHOR(S)
Shaheen, R.; Janssen, C.; Röckmann, T.
PUB. DATE
January 2007
SOURCE
Atmospheric Chemistry & Physics;2007, Vol. 7 Issue 2, p495
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Contrary to tropospheric CO2 whose oxygen isotopic composition follows a standard mass dependent relationship, i.e. δ17O∼0.5 δ18O, stratospheric CO2 is preferentially enriched in 17O, leading to a strikingly different relation: δ17O∼1.7 δ18O. It has been shown repeatedly that the isotope anomaly is inherited from O3 via photolytically produced O(¹D) that undergoes isotope exchange with CO2 and the anomaly may well serve as a tracer of stratospheric chemistry if details of the exchange mechanism are understood. We have studied the photochemical isotope equilibrium in UV-irradiated O2-CO2 and O3-CO2 mixtures to quantify the transfer of the anomaly from O3 to CO2 at room temperature. By following the time evolution of the oxygen isotopic compositions of CO2 and O2under varying initial isotopic compositions of both, O2/O3 and CO2, the isotope equilibria between the two reservoirs were determined. A very strong dependence of the isotope equilibrium on the O2/CO2-ratio was established. Equilibrium enrichments of 17O and 18O in CO2 relative to O2diminish with increasing CO2 content, and this reduction in the equilibrium enrichments does not follow a standard mass dependent relation. When molecular oxygen exceeds the amount of CO2 by a factor of about 20, 17O and 18O in equilibrated CO2 are enriched by (142±4)‰ and (146±4)‰, respectively, at room temperature and at a pressure of 225 hPa, independent of the initial isotopic compositions of CO2 and O2or O3. From these findings we derive a simple and general relation between the starting isotopic compositions and amounts of O2and CO2 and the observed slope in a three oxygen isotope diagram. Predictions from this relation are compared with published laboratory and atmospheric data.
ACCESSION #
24264755

 

Related Articles

Share

Read the Article

Courtesy of THE LIBRARY OF VIRGINIA

Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics