Infrared spectroscopy of
halogen-containing species for
atmospheric remote sensing
Jeremy J. Harrison
University of York
Atmospheric Chemistry Experiment (ACE)
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FTS: 750 to 4400 cm-1
Radiance of sun gives high S/N
Long pathlengths ~ 300 km (limb sounding)
Measurements at many altitudes
ACE detects more trace organic molecules
than any other satellite instrument.
Halocarbons
 Strong greenhouse
gases
 Many are ozone
depleting substances
– Regulated by the
Montreal Protocol
 Many are increasing
in the atmosphere
 Many have long
atmospheric lifetimes
Laboratory Spectroscopy
 GEISA and HITRAN contain a number of absorption
cross section datasets for Cl- and F-containing
molecules
 Dataset requirements for remote sensing:
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Accurate band intensities
Accurate wavenumber scale
Wide P-T coverage for best interpolation
Appropriate resolution (Doppler-limited)
 A number of GEISA / HITRAN datasets fail in many of
these respects.
MSF at RAL
Bruker IFS
125 HR
26-cm
absorption cell
CFC-12 (CCl2F2)
 Most abundant anthropogenic
halocarbon in the atmosphere
 Was used in refrigeration and
air conditioning
 Banned under the Montreal
Protocol
 Atmospheric lifetime ~ 100
years
MIPAS:
Kellmann et al., ACP, 12, 11857–11875, 2012
CFC-12 absorption cross sections in
HITRAN / GEISA
CCl2F2 cross sections
CCl2F2
(CFC-12)
Main problems with old dataset:
– Strong Q branch near 1160 cm-1
often saturated.
– Wavenumber calibration error
CCl2F2 cross sections
CCl2F2 cross sections
Carbon tetrachloride
 CCl4 accounted for 359 ppt (about 11%) of total
tropospheric Cl in 2008
 CCl4 tropospheric abundances have declined less
rapidly than expected
 Atmospheric lifetime 26 years
 Top-down emissions 40–80 Gg/yr (2005–2008)
 Bottom-up emissions 0–30 Gg/yr (2005–2008)
 Errors in reporting, errors in the analysis of
reported data, and/or unknown sources?
 ACE-FTS CCl4 data product biased ~20% high
CCl4 absorption cross sections in
HITRAN / GEISA
CCl4 cross sections
CCl4
Main problems with old dataset:
– Spectra under-resolved
– Wavenumber calibration error
CCl4 cross sections
CCl4 cross sections
HCFC-22 (CHClF2)
 Most abundant HCFC (substitutes for long-lived
ozone-depleting substances)
 Lifetime 11.9 years
 HCFC-22 increased at a rate of about 8 ppt/yr
(4.3%/yr) during 2007–2008, more than 50%
faster than observed in 2003–2004
– Rapidly increasing HCFC-22 production in developing
countries
 Emissions are projected to begin to decline during
the coming decade due to measures already
agreed to under the Montreal Protocol
HCFC-22 absorption cross sections in
HITRAN / GEISA
CHClF2 cross sections
CHClF2
(HCFC-22)
Main problems with old dataset:
– Poor P-T coverage
– Wavenumber calibration error
CHClF2 cross sections
Hydrofluorocarbons (HFCs)
 Hydrofluorocarbons (HFCs) are replacements for
CFCs and HCFCs
– Not regulated by Montreal Protocol
 Trifluoromethane (HFC-23, CHF3)
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Second most abundant HFC in atmosphere
Lifetime of 222 years
100-year GWP of 14,200
Formed as a by-product of HCFC-22 (CHClF2) production
 1,1,1,2-Tetrafluoroethane (HFC-134a, CF3CH2F)
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Most abundant HFC in atmosphere
Lifetime of 13.4 years
100-year GWP of 1,370
The preferred refrigerant in refrigeration and mobile air
conditioning (replacement for CFC-12)
Previous HFC-23 absorption cross
sections
Remote-sensing observations of HFC-23
Harrison et al., First remote-sensing observations of
trifluoromethane (HFC-23) in the upper troposphere and lower
stratosphere, J. Geophys. Res., 2012, 117, D05308,
doi:10.1029/2011JD016423.
CHF3 cross sections
New dataset:
Harrison, JQSRT
130, 359-364
(2013)
Main problems with old dataset:
CHF3 (HFC-23)
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Very poor P-T coverage
Spectra under-resolved
Inconsistent baselines
Wavenumber calibration error
Remote-sensing observations of HFC-134a
Nassar et al., J. Geophys. Res., 2006, 111, D22313,
doi:10.1029/2006JD007395.
HFC-134a absorption cross sections in
HITRAN / GEISA
CF3CH2F cross sections
Main problems with old dataset:
– Poor P-T coverage
– Wavenumber calibration
error
CF3CH2F
(HFC-134a)
CF3CH2F cross sections
Acknowledgements
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Funding from NERC (UK) & NCEO
RAL – Gary Williams & Robert McPheat
NCEO – John Remedios
ACE – Chris Boone & Peter Bernath