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AR226-1520 Telomer Research Program RECEIVED OPPT NCIC Report Title: Study of the Atmospheric Fate of Fluorinated Alcohols 03 SEP 30 PM 13:30 Author(s): Georges LeBras, Valrie Bossoutrot, and Isabelle Magneron Contractor: Centre National de la Recherche Scientifique - Laboratoire de Combustion et Systemes Reactifs (CNRS - LCSR), Orlans, France Study Dates: November 2001 - March 2003 (final report July 2003) Study Objective The central aim of the study was to characterize the atmospheric fate of C8F17CH2CH2OH (2perfluoro-n-octyl ethanol; 2POE). Preliminary tests made in the CNRS-Orlans photoreactor showed that this substance could not be investigated directly due to its low vapor pressure. The alternative approach was to investigate shorter chain fluorinated alcohols as surrogates of 2POE. Accordingly, the rate constants of CF3CH2CH2OH (trifluoropropanol; TFP) and C6F13CH2CH2OH (tridecafluoro-octanol; TDO) with OH radical, the major atmospheric oxidant, have been measured and the OH-initiated oxidation mechanism of TFP in air has been determined at room temperature. The were carried out using two photoreactors: a 150 L Teflon bag irradiated by lamps at CNRS-Orlans for the kinetics and mechanistic studies, and the 200 m3 European photoreactor, EUPHORE, irradiated by sunlight at Valencia (Spain) also for the mechanistic study. Materials and Methods The kinetic rate constants of TFP and TDO with OH radicals were measured at Orlans in a simulation chamber comprised of a 150 L Teflon bag irradiated by UV lamps. OH radicals were produced by the photolysis of H2O2 at 254 nm. The time profiles of reactant consumption and product formation were obtained Fourier Transformed Infrared (FTIR) Spectroscopy and Gas phase Chromatography coupled with a Flame Ionisation Detection (GC/FID). FTIR analysis was made in a Nicolet White gas cell of 2 L and 25 cm length with an optical multipath of 10 m. Analysis was at atmospheric pressure with 2 L samples taken from the reaction mixture for each FTIR analysis. For GC/FID analysis a smaller volume of around 0.1 L was sampled from the chamber and flushed into the GC/FID system. FID detects a large variety of organic compounds but cannot detect short chain compounds such as formaldehyde (HCHO). A mass spectrometer coupled to the GC was used to follow the time evolution of the ionised fragments and gives qualitative information about the products formed. Concentration time profiles of reactants were obtained by FTIR or GC analysis. The reaction rate constants were obtained by the relative rate method using a reference compound. Liquid reactants are introduced into the bag through a flow of purified air by Does not contain TSCA CBI 1 TRP (30-Sept-2003) flushing a known amount of liquid placed in a bubbler. The photoreactor is then filled to its full capacity at atmospheric pressure with purified air. The alcohol, the reference compound and H2O2 were successively introduced into the reactor. Before starting the reaction by switching on the lamps, at least three analyses were performed to check the homogeneity and the stability of the gas mixture. The reaction mechanism experiments were performed using the simulation chamber at Orlans described above and the European photoreactor, EUPHORE, installed at Valencia in Spain. The EUPHORE facility consists of two independent hemispherical outdoor simulation chambers, made of FEP foil, each having a volume of 200 m3. The facility has many analytical instruments, including FTIR, GC-FID, HPLC, for in-situ analysis or after sampling. The detection sensitivity is high enough to use VOC and NOX concentration ranges close to those present in the atmosphere. While the high volume of EUPHORE allows many samples and the low area/volume ratio (1 m-1) limits wall artifacts, some experimental parameters (in particular temperature and sunlight) can not be controlled. In Orlans, the OH initiated decomposition of TFP both with and without NOX was studied and a reaction mechanism was inferred. Reaction proceeds by H-abstraction from the -CH2- group in -position to the alcohol moiety. Subsequent experiments at EUPHORE confirmed these results. Findings The primary atmospheric decay mechanism for fluoroalcohols of type CnF2n+1CH2CH2OH is by reaction with OH radicals. The rate constant measured using a relative method are k = (1,06 0,10) x 10-12 for OH + TFP reaction and k = (0,99 0,18) x 10-12 for the OH + TDO reaction at 298 K (units of cm3 molecule-1 s-1). The same values obtained indicate that the nature of the perfluorinated group has no influence on the reactivity of the alcohol. Therefore, the above value of the rate constant can be recommended for the reaction OH + 2POE, i.e. k = (1,0 0,2) x 10-12 cm3 molecule-1 s-1 at 298 K. For the OH-initiated oxidation of TFP, the major products observed are the fluoroaldehydes CF3CH2CHO and CF3CHO, in the presence and absence of NOX. PAN like compounds were also observed in the presence of NOX, but in the atmosphere, the contribution of PAN-like compounds derived from fluoroalcohols will be negligible compared to PAN produced from other biogenic and anthropogenic sources. The yield of the primary aldehyde, CF3CH2CHO, was found close to 50 % within the uncertainty of measurements, both in the presence and absence of NOX. However a yield close to unity can not be excluded considering the uncertainties. The obtained results are consistent with a mechanism where the primary OH-reaction proceeds by Hatom abstraction from the CH2 group in -position of the -OH group. Then CF3CH2CHO and CF3CHO are successively formed, CF2O being the end product. PAN compounds can also be formed in the presence of NOX. This mechanism can be generalised for the larger fluoroalcohols, including TDO and 2POE. In this case the intermediate aldehydes are CnF2n+1CH2CHO and CnF2n+1CHO. Does not contain TSCA CBI 2 TRP (30-Sept-2003) Conclusion Regarding the atmospheric implications of the obtained results, the atmospheric lifetime ( = 1/ k[OH]) of TFP, TDO and 2POE is estimated to be 11 days. Hence, these fluoroalcohols could be transported over long distances before being oxidised. However, this lifetime is too short to make these compounds significant contributors to radiative forcing. Concerning the oxidation products, the fluoroaldehydes CnF2n+1CH2CHO will have a short lifetime (~ 4 days) resulting from their reaction with OH (photolysis would be less important as suggested by EUPHORE experiments). The fluoroaldehydes subsequently formed, CnF2n+1CHO, will react much more slowly with OH, the lifetime of the reference compound CF3CHO toward OH being ca 20 days (k OH + CF3CHO ~ 5 x 10-13 cm3 molecule-1 s-1 at 298 K)1. This lifetime is comparable to that of the uptake of such soluble species by clouds2. However, the importance of cloud processing of the fluoroaldehydes will depend on their loss rate by photodissociation which needs to be better defined. (The EUPHORE experiments have suggested a lifetime of the fluoroaldehydes higher than 6 days). The gas phase degradation of CnF2n+1CHO (OH reaction or photolysis) will ultimately produce CF2O which is relatively soluble and will be removed by uptake in cloud or rainwater. The importance of the alternative PAN like compounds will depend on their stability. However, their contribution as NOX reservoir should be negligible regarding to PAN which is produced from hydrocarbons emitted in much larger amounts compared to fluoroalcohols. Publications / Presentations: None to date. 1 Scollard D. J., Treacy J. J., Sidebottom H. W, Balestra-Garcia C., Laverdet G., Le Bras G., Mac Leod H., Tton S. Rate constants for the reactions of hydroxyl radicals and chlorine atoms with halogenated aldehydes. J. Phys. Chem., 97, 4683 (1993). 2 WMO, 1994. Scientific Assessment of Ozone Depletion. Report n 37, World Meteorological Organization. Does not contain TSCA CBI 3 TRP (30-Sept-2003)