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EC number: 204-126-9
CAS number: 116-14-3
Using the rate constant measured by Acerboni et al (1999) and an average °OH concentration of 10E6 molecule/cm3 (Prinn et al, 1995), the corresponding atmospheric lifetime is calculated to be approximately 1 day and the half life 0.69 day. Acerboni et al (2001), using the same rate constant in a 3 -dimensional chemical transport model (representing more closely the average behaviour of TFE in the atmosphere), predicted an °OH related lifetime of 1.9 days for TFE. Main atmospheric degradation product carbonyl fluoride hydrolyses in atmospheric water to form carbon dioxide (CO2) and hydrogen fluoride (HF) as end products, the HF being removed by rain (wash out).
The physico-chemical properties of TFE, i.e. its high vapour pressure,
indicate that it should remain essentially in the gas phase.
TFE can react with hydoxyl radical (°OH) through addition on the double
bond. Other atmospheric species can also react with TFE, in particular
ozone (O3) and the nitrate radical (NO3°). The
value of the rate constant for the reaction of TFE with °OH has been
measured (Orkin et al, 1997; Acerboni et al, 1999) For comparison
purposes Table A lists these rate constants.
Table A: °OH rate constants of TFE.
Using the rate constant measured by Acerboni et al (1999) and an average
°OH concentration of 10E6 molecule/cm3 (Prinn et al,
1995), the corresponding atmospheric lifetime is calculated to be
approximately 1 day and the half life 0.69 day. Acerboni et al (2001),
using the same rate constant in a 3 -dimensional chemical transport
model (representing more closely the average behaviour of TFE in the
atmosphere), predicted an °OH related lifetime of 1.9 days for TFE.
However, whilst the use of a mean tropospheric
°OH concentration of 10E6 molecule/cm3 is scientifically
justified, the EU TGD (Part 2, Page 51) recommends a vaule of 5 x 10E5
molecule/cm3. If the latter value were adopted, this would
double the °OH + TFE lifetime to 3.8 days and increase the relative
significance of the O3 + TFE sink.
TFE can equally react with ozone (O3). Several authors have
reported values of the rate constant and lifetime for this pathway.
Table B: Reaction of TFE with O3
a Assuming an O3 concentration of 7x 10E11
b As cited by Acerboni et al, 1999
Thus, the O3 -related lifetime of TFE may range from 33 days
to 9 years. The lifetime is calculated from the O3 + TFE rate
constant, assuming an ozone concentration of 26 ppbv (which is
reasonable for the atmospheric background level). This rate constant
should depend only on temperature (and indeed only slightly). The large
discrepancy, from one study to another, probably indicates that what
some authors were observing was not (only) the reaction of O3
with TFE. Acerboni et al (1999) measured the lowest rate constant, when
performing their determination in the presence of cyclohexane, added to
scavenge °OH and other radicals. In the absence of this additive, they
found a rate constant about a factor of 10 higher. They suggest that
secondary chemistry may have contributed to the loss of TFE in previous
investigations, resulting in higher apparent rate constants. This seems
quite likely. Importantly, however, even if the fastest rate constant,
i.e. that of Heicklen (1966), is adopted, the resulting estimated
lifetime of 33 days with respect to the O3 + TFE reaction
implies that this sink is a very minor one compared to the °OH + TFE
reaction (lifetime < 2 days, or < 4 days if an °OH concentration of 5 x
10E5 molecule/cm3 is adopted).
Acerboni et all (1999) also studied the possible reaction of TFE with NO3°.
Her model calculations suggest that, due to the lifetime of >156 days
associated with this reaction, only a small part of the TFE would be
converted in this manner.
In all, the average atmospheric lifetime of TFE is considered to be < 2
days (t1/2 = 1.32 days for lifetime of
1.9 days Acerboni 2001).
The main oxidation pathway for TFE in the atmosphere, reaction with °OH,
yields carbonyl fluoride C(=O)F2 as the main degradation
product. Carbonyl fluoride hydrolyses in atmospheric water to form
carbon dioxide (CO2) and hydrogen fluoride (HF) as end
products, the HF being removed by rain (wash out). The lifetime of this
process for carbonyl fluoride is expected to be of the order of 5 to 10
days. However, in a global 3 -dimensional modelling study, Kanakidou et
al (1995) have calculated a tropospheric lifetime for C(=O)F2
with respect to uptake and hydrolysis in clouds of 3.9 - 7.1 days.
Acerboni G, Jensen NR, Rindone B, Hjorth J. 1999. Kinetics and products
formation of the gas-phase reactions of tetrafluoroethylene with OH and
NO3 radicals and ozone. Chemical Physics Letters 309: 364-368.
Acerboni G, Beukes JA, Jensen NR, Hjorth J, Myhre G, Nielsen CJ, Sundet
JK. 2001. Atmospheric degradation and global warming potentials of three
perfluoroalkenes. Atmospheric Environment 35: 4113-4123.
Prinn RG, Weiss RF, Miller BR, Huang J, Alyea FN, Cunnold DM, Fraser PJ,
Hartley DE, Simmonds PG. 1995. Atmospheric trends and lifetime of CH3Cl3
and global OH concentrations. Science 269: 187 – 192.
Orkin VL, Huie RE, Kurylo MJ. 1997. Rate constants for the reactions of
OH with HFC 245cb (CH3CF2CF3) and some fluoroalkenes (CH2CHCF3,
CH2CFCF3, CF2CFCF3, and CF2CF2), J Phys Chem A: 101, pp. 9118 – 912.
Adeniji SA, Kerr JA, Williams MR. 1981. Rate constants
for ozone-alkene reactions under atmospheric conditions. Int J Chem
Kinet 13: 209-217.
Heicklen J. 1966. J Phys Chem 70: 477 with correction sheet added by the
author to page 480 (as cited by Acerboni et al, 1999.)
Toby FS, Toby S. 1976. J Phys Chem 80: 2313 (as cited by Acerboni et al,
Kanakidou M, Dentener FJ, Crutzen PJ. 1995. A global three-dimensional
study of the fate of HCFCs and HFC-134a in the troposphere. Journal of
Geophysical Research 100 (D9), 18781-18801
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