Abstract

Samples of background air were collected in thelower troposphere of the Northern (high Arctic,northern Ontario, Vancouver and Houston) andSouthern (Baring Head, New Zealand) Hemispheresover the period July 1999 until March 2001.These samples were analysed for the stablecarbon isotope ratios of1,1,1-trichlorotrifluoroethane (CFC113) andCH3Cl using a gaschromatography-continuous flow on-linecombustion isotope ratio mass spectrometrycombination. For CH3Cl the global averageof the stable carbon isotope ratio is −36.2± 0.3‰ (error of mean). The average isbased on 78 data points, standard deviation forall measurements is 2.3‰, and the 90%confidence interval is −35.8 to −36.6‰.However, the number of data points from theSouthern Hemisphere is rather limited and thusthis observation is not necessarilyrepresentative for the entire SouthernHemisphere. A simple isotopic budget ofCH3Cl shows the most important parametersneeding to be defined are the kinetic isotopeeffect of CH3Cl destruction by OH radicalsand the source composition of CH3Clemitted by the oceans and biomass burning ofC-4 plants. Present budgets of atmosphericCH3Cl show a significant deficit in thesource strength. We estimate that the averagestable carbon isotope ratio of the additionalCH3Cl emissions required to balance thebudget is −41.9 ± 7.8‰. The averageCFC113 isotopic composition based on 38measurements is −23.3 ± 1.6‰ (error ofmean), σ = 9.6‰ with no significantdifference between the hemispheres.

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

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.