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phototransformation in air
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference Type:
Report date:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline draft (Photochemical Oxidative Degradation in the Atmosphere)
Principles of method if other than guideline:
Methods were equivalent to those discussed in the OECD guideline draft, namely flash photolysis methods, covering absolute and relative rate.
GLP compliance:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Test material form:

Study design

Estimation method (if used):
Estimation was calculated using the formula:


where Τ(CF3CF2CF2CF2CF2CHF2) and T(CH3CCl3) represent the tropospheric lifetimes of CF3CF2CF2CF2CF2CHF2 and CH3CC13 through reaction with OH radicals,

and Κ CH3CCl3 and K CF3CF2CF2CF2CF2CHF2 represent the rate constants for the reactions of CH3CCh and CF3CF2CF2CF2CF2CHF2 with OH radicals at 272 K.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
Details on light source:
EG&G FX-1930, typically 800 V and 2 µF
Details on test conditions:
Absolute Rate Method

A Pyrex glass reactor with an inner diameter of 25 mm and a length of about 40 cm was used for the FP- LIF and LP-LIF experiments. For the FP-LIF method, OH radicals were produced by the pulsed photolysis of H2O by a Xe flash lamp (EG&G FX-1930, typically 800 V and 2 µF) in the presence of a large excess of argon bath gas. For the LP-LIF method, OH radicals were produced by the reaction O(^1 D) + H2O -+ 2OH in the presence of a large excess of helium or argon bath gas. O(^1 D) atoms were generated by photodissociation of N2O with an ArF excimer laser. For both LP and FP methods, initial concentration of OH radicals were always kept smaller than 10^11 molecule cm^-3 to prevent accumulation of photofragmentation products, reaction products, or both, all photolysis experiments were carried out under slow-flow conditions. The repetition rates of the FP lamp and excimer laser were set at 10 Hz.

The excitation light for the FP-LIF and LP-LIF methods was from a frequency-doubled tuneable dye laser (pumped by the second-harmonic of a Nd:YAG laser, 10 Hz), and the wavelength was tuned at about 308 nm. The fluorescence signal from the OH radicals was monitored at about 308 nm. A monochromator was used to limit the amount of scattered excitation light (and photolysis light) reaching the photomultiplier tube that was used to monitor the fluorescence signals. The signals were accumulated by a multichannel scaler/averager.

The flow rate of each gas was measured and controlled by calibrated mass flow controllers. The total gas pressure of the reactor was monitored by using a capacitance manometer and was kept constant by an electrically controlled exhaust throttle valve. The temperature of the reactor was maintained either by an electric heater or by circulating fluid through the outer jacket of the reactor from a thermostated bath. The temperature was measured with a CA (type K) thermo­ couple. During the experiments, the temperature across the reaction volume was maintained at better than ±2 K over the temperature range examined. To ensure that the experimental data were free from unexpected daily fluctuation of experimental conditions and experimental setup, the experiments were repeated at intervals from several days to several months under a variety of experimental conditions.

Relative Rate Method

Experiments were performed in a previously described 11.5-dm^3 quartz cylindrical chamber (10-cm i.d., 146 cm long) with an external jacket. The chamber temperature (253-328 K) was controlled by circulating heated water or a coolant (PF-5060; Sumitomo 3M Ltd.) through the external jacket. A/ constant-temperature bath (GT50L; Thermo Haake Co., Germany) was used to maintain the temperature of the circulating fluid. Ten low-pressure Hg lamps (GL- 40; National Co., Japan) surrounding the chamber were used as the light source.

The initial concentrations (in units of molecules cm^-3) were 5.0 x 10^14 (CF3CF2CF2CF2CF2CHF2), 5.0 x 10^14 (reference compound), and ~5.8 x 10^17 (H20) in 200 Torr of He. He was used because of its low 0(^1D) quenching efficiency. CHF2Cl (HCFC- 22) and CH2FCF3 (HFC-134a) were used as reference compounds. A greaseless vacuum line was used in preparing the reaction gas mixtures. An O3/O2 (3%) gas mixture, which was generated from pure O2 with a silent-discharge ozone generator (ECEA-1000; Ebara­jitsugyo, Japan), was continuously introduced into the chamber at a flow rate of 10-50 cm^3 min^-1 during the UV irradiation. A steady-state high OH radical con­ centration of (0.53-1.2) x 10 15 molecule cm=' can be produced in the chamber by using this technique. The flow rate of the O3/O2 gas mixture was controlled by a mass flow controller. In all experiments, the initial pressure in the chamber was 200 Torr. The total pressure increased during irradiation and reached 300- 500 Torr by the end of the experiment.
Reference substance:

Results and discussion

Degradation rate constant
Key result
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 s-1
Transformation products:

Applicant's summary and conclusion

Validity criteria fulfilled:
Using both absolute and relative rate methods, we determined the rate constants for the reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals over the temperature range 250-430 K: k, = (4.71 ± 0.94) x 10-13 exp[-(1630 ± 80)/T] cm^3 molecule-1 s-1. The FP-LIF and LP-LIF techniques were employed in the absolute method, and CHF2Cl and CH2FCF3 were used as reference compounds in the relative rate method. The rate constants determined by the two methods agreed with each other within the experimental uncertainties. This fact implies that the k data obtained in this study have a high reliability. The tropospheric lifetime of CF3CF2CF2CF2CF2CHF2 through reaction with OH radicals was estimated to be 31 years.
Executive summary:

The rate constants k1for the reaction of CF3CF2CF2CF2CF2CHF2with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250 - 430 K using the flash photolysis-laser-induced fluorescence (FP-LIF) technique and the laser photolysis-laser-induced fluorescence (LP-LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253 - 328 K in an 11.5-dm3reaction chamber with either CHF2CI or CH2FCF3as a reference compound. OH radicals were produced by UV photolysis of an O3-H2O-He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k1(298 K) values determined by the absolute method were (1.69± 0.07) x 10-15cm3molecule-1s-1(FP-LIF method) and (1.72 ± 0.07) x 10-15cm3molecule-1s-1(LP-LIF method). Whereas the k1(298 K) values determined by the relative method were (1.87 ± 0.11) x 10-15cm3molecule-1s-1(CHF2CI reference) and (2.12 ± 0.11) x 10-15cm3molecule-1s-1(CH2 FCF3 reference). These data are consistent with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was k1= (4.71 ± 0.94) x 10-13 exp[-(1630± 80)/T] cm3molecule-1s-1. Using kinetic data for the reaction of tropospheric CH3CCl3with OH radicals [k1(272 K) = 6 0 x 10-15cm3molecule-1s-1, tropospheric lifetime of CH3CCl3= 6.0 years]. We estimated the tropospheric lifetime of CF3CF2CF2CF2CF2CHF2through reaction with OH radicals to be 31 years.