Study of the Atmospheric Degradation, Radiative Forcing and Global Warming Potentials of CH2FCH2OH, CHF2CH2OH and CF3CH2OH

S. R. Sellevåga, G. Myhreb, J. K. Sundetb and C. J. Nielsena

a Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, 0315 Oslo, Norway b Department of Geophysics, University of Oslo, P.O. Box 1022 Blindern, 0315 Oslo, Norway

INTRODUCTION

This work is a part of the project “Impact of Alternative Fluorinated Alcohols and Ethers on the Environment (IAFAEE)”, which is a co-operation between Uni-versity of Oslo, University College Dublin, University of Crete and Russian Academy of Science. We have studied the atmospheric degradation, radiative forcing and global warming potentials (GWP) of CH2FCH2OH, CHF2CH2OH and CF3CH2OH, which have been suggested as new CFC and HCFC replacements. See also posters AP6 and AP12.

RESULTS

Rate Constants for the Reactions with OH Radicals

Fig. 1. Loss of reactant versus reference in the reaction with OH.

Table 1. Rate constants for the OH reactions with CH2FCH2OH, CHF2CH2OH, and CF3CH2OH at 298 K.

Absorption Cross Sections

Fig. 2. Absorption cross sections (base e) of pure vapors of CH2FCH2OH, CHF2CH2OH and CF3CH2OH.

Radiative Forcing and Global Warming Potentials

Fig. 3. Zonal mean vertical distribution of CF3CH2OH given in ppt. The abundance decrease much faster with altitude than for well mixed greenhouse gases but to a smaller extent than for the two other compounds in this study.

Fig. 4. Geographical distribution of radiative forcing due to CF3CH2OH. The glo-bal mean radiative forcing is 0.17 W m-2. Similar to the well mixed greenhouse gases the largest radiative forcing is in tropical regions with small cloud amounts, high surface temperature, and a large temperature difference between the surface and the tropopause.

Table 2. Atmospheric lifetimes based on the OH reaction rate constants from this work.

Table 3. GWP values relative to CO2 and CFC-11 for three time horizons.

CONCLUSIONS

The impact of CH2FCH2OH, CHF2CH2OH and CF3CH2OH on the Earth's radiative balance is negligible. With a lifetime of 71 days, however, a large part of CF3CH2OH will enter into droplets and end up as TFA.

METHODSThe relative rate measurements were performed in synthetic air at 1013 15 hPa and 298 2 K in a 250 L smog chamber with in situ FTIR detection. Hydroxyl radicals were generated by photolysis of ozone/water mixtures. Typical volume fractions were: 5-10 ppm of each organic compound and ca. 103 ppm of both water and ozone.

The measurements of absolute integrated absorption intensities were carried out at 298 2 K using a Bruker IFS 113v spectrometer and DTGS detectors. A Ge/KBr beamsplitter was used in the MIR region, while 3.5 μm Mylar film was used in the FIR region. Single channel spectra of pure vapours were recorded in the region 4000-70 cm-1 with 1.0 cm-1 resolution and adding 512 scans. The pressures of the samples were in the range between 2 and 20 hPa, and were measured using a MKS Baratron Type 122A pressure gauge.

The atmospheric distributions of CH2FCH2OH, CHF2CH2OH and CF3CH2OH were cal-culated using the Oslo CTM2 model, which is an off-line chemical transport/tracer model. The model uses pre-calculated transport and physical fields to simulate chemical turnover and dist-ribution in the atmosphere. It is valid for the global troposphere and is three-dimensional with the model domain reaching from the ground up to 10 hPa (see e.g. ref. [4] for a further description). The radiative forcing calculations were carried out using a thermal infrared broad band model (details of the model are given in ref. [5]). CH2FCH2OH, CHF2CH2OH and CF3CH2OH were included with 5, 6 and 8 bands, respectively.

[1] Kelly, T., Sidebottom, H., Unpublished.[2] Wallington, T.J., et al. (1988) J. Phys. Chem. 92, 5024-5028.[3] Tokuhashi, K., et al. (1999) J. Phys. Chem. 103, 2664-2672.[4] Acerboni, G., et al. (2001) Atmos. Environ. 35, 4113-4123.[5] Myhre, G., Stordal, F. (1997) J. Geophys. Res. 102, 11181-11200.

0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

y = (-0.017±0.049) + (5.907±0.448) * x

ln {

[CH

2FC

H2O

H] 0/[

CH

2FC

H2O

H] t}

ln {[CH3CH

3]

0/[CH

3CH

3]

t}

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

y = (0.0058±0.0050) + (1.878±0.023) * x

ln {

[CH

F2C

H2O

H] 0/[

CH

F2C

H2O

H] t}

ln {[CH3CH

3]

0/[CH

3CH

3]

t}

0.0 0.1 0.2 0.3 0.40.00

0.04

0.08

0.12

0.16

0.20 y = (0.0065±0.0049) + (0.513±0.025) * x

ln {

[CF

3CH

2OH

] 0/[C

F3C

H2O

H] t}

ln {[CH3CH

3]0/[CH

3CH

3]t}

4000 3500 3000 2500 2000 1500 1000 500

0.0

0.1

0.2

0.3

0.4 CH2FCH

2OH

Ab

sorp

tio

n c

ross

sec

tio

n

/(10

-18 c

m2 m

ole

cule

-1)

Wavenumber/cm-1

4000 3500 3000 2500 2000 1500 1000 500

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

CHF2CH

2OH

Ab

sorp

tio

n c

ross

sec

tio

n/(

10-1

8 cm

2 mo

lecu

le-1)

Wavenumber/cm-1

4000 3500 3000 2500 2000 1500 1000 500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

CF3CH

2OH

Ab

sorp

tio

n c

ross

sec

tio

n

/(10

-18 c

m2 m

ole

cule

-1)

Wavenumber/cm-1