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Insights into Mechanistic Models for Evaporation of Organic Liquids in the Environment Obtained by Position-Specific Carbon Isotope Analysis

Julien, Maxime, Nun, Pierrick, Robins, Richard J., Remaud, Gérald S., Parinet, Julien, Höhener, Patrick
Environmental Science & Technology 2015 v.49 no.21 pp. 12782-12788
carbon, distillation, ethanol, evaporation, mechanistic models, monitoring, nuclear magnetic resonance spectroscopy, polar compounds, pollutants, remediation, stable isotopes, volatilization
Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring ¹³C nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig–Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor–liquid contribution that is strongly position-specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid–vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig–Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.