Infrared spectroscopy of halogen-containing species for atmospheric remote sensing Jeremy J. Harrison University of York

 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. Atmospheric Chemistry Experiment (ACE)

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

 GEISA and HITRAN contain a number of absorption cross section datasets for Cl- and F-containing molecules  Dataset requirements for remote sensing: –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. Laboratory Spectroscopy

Bruker IFS 125 HR MSF at RAL 26-cm absorption cell

CFC-12 (CCl 2 F 2 )  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

CCl 2 F 2 (CFC-12) Main problems with old dataset: –Strong Q branch near 1160 cm -1 often saturated. –Wavenumber calibration error CCl 2 F 2 cross sections

Carbon tetrachloride  CCl 4 accounted for 359 ppt (about 11%) of total tropospheric Cl in 2008  CCl 4 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 CCl 4 data product biased ~20% high

CCl 4 absorption cross sections in HITRAN / GEISA

CCl 4 CCl 4 cross sections Main problems with old dataset: –Spectra under-resolved –Wavenumber calibration error

CCl 4 cross sections

HCFC-22 (CHClF 2 )  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

CHClF 2 (HCFC-22) CHClF 2 cross sections Main problems with old dataset: –Poor P-T coverage –Wavenumber calibration error

CHClF 2 cross sections

 Hydrofluorocarbons (HFCs) are replacements for CFCs and HCFCs –Not regulated by Montreal Protocol  Trifluoromethane (HFC-23, CHF 3 ) –Second most abundant HFC in atmosphere –Lifetime of 222 years –100-year GWP of 14,200 –Formed as a by-product of HCFC-22 (CHClF 2 ) production  1,1,1,2-Tetrafluoroethane (HFC-134a, CF 3 CH 2 F) –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) Hydrofluorocarbons (HFCs)

Previous HFC-23 absorption cross sections

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: /2011JD Remote-sensing observations of HFC-23

CHF 3 cross sections CHF 3 (HFC-23) Main problems with old dataset: –Very poor P-T coverage –Spectra under-resolved –Inconsistent baselines –Wavenumber calibration error New dataset: Harrison, JQSRT 130, (2013)

Nassar et al., J. Geophys. Res., 2006, 111, D22313, doi: /2006JD Remote-sensing observations of HFC-134a

HFC-134a absorption cross sections in HITRAN / GEISA

CF 3 CH 2 F cross sections CF 3 CH 2 F (HFC-134a) Main problems with old dataset: –Poor P-T coverage –Wavenumber calibration error

CF 3 CH 2 F cross sections

Acknowledgements  Funding from NERC (UK) & NCEO  RAL – Gary Williams & Robert McPheat  NCEO – John Remedios  ACE – Chris Boone & Peter Bernath