ULg contributions to AGACC-II: main results for 2013

1. ULg contributions to AGACC-II: main results for 2013 Team members: W. Bader, B. Bovy, P. Demoulin, O. Flock, B. Franco, B. Lejeune, E. Mahieu, C. Servais, D. ZanderG. Roland and R. Zander emmanuel.mahieu@ulg.ac.be

2. ULg involvement • Contribution to WP1 (monitoring of direct GHGs): • Deliver long-term time series of major GHGs (CO2, CH4, N2O), including the exploitation of historical grating observations • Investigations of CCl4 and CF4: retrieval strategies and trends • Contribution to WP2 (VOCs & CFC substitutes): • Development or optimization of retrieval strategies for CH3Cl, CH3OH, C2H6, C2H4 (see Corinne’s talk) ,H2CO and CFC-substitutes • Contribution to WP5 (outreach): publications, archiving… • Essentially based on the exploitation of long-term (FT)IR measurements under clear-sky conditions at the Jungfraujoch station (NDACC site, Swiss Alps, 46.5ºN, 8.0ºE, 3580 m asl): • Grating IR spectra available since 1976 • FTIR spectra since 1984, current measurement density: >130 d/yr

3. WP1 results Analysis of historical grating spectra: search for appropriate CO2 lines/windows

4. The Jungfraujoch grating spectrometer • A 7.3 m focal length Ebert/Fastie grating spectrometer was installed at the Jungfraujoch in the late 1950s, it was first used to record solar atlases (IR, vis and near-UV) • As of 1976, the instrument was used in double-pass mode to record narrow atmospheric solar spectra (InSb detector), encompassing absorption lines of specific target gases, e.g. HF, HCl, N2O, CH4 • Various diffraction orders have been used over 1976 to 1989 => several observational subsets

5. Searching for CO2 lines… • Conversely to CH4 and N2O, CO2 was not a specific target of the pioneering observational effort • Four windows encompassing CO2 lines have been identified (resolution between 7 and 13 mK): • BUT first FTIR data in 1984 => no ext. back in time…

6. Preliminary fittings (B-D windows)

7. WP1 results (ctd) Retrievals of carbon tetrafluoride (CF4) from ground-based FTIR spectra

8. Carbon tetrafluoride – CF4 • The retrieval strategy (simple scaling) has been finalized: two consecutive runs allow improving the precision of the retrievals; the 2nd window focuses on the most interference-free features of CF4 (i.e. avoiding the center of the window (HDO & H2O)) • A two-decade time series has been produced and analyzed, the “wet-spectra” are excluded • Mean relative standard deviation around the daily averages (inv. ≥ 4 meas.): <1%!

9. Carbon tetrafluoride – CF4 • First FTIR time series for this very long-lived GHG • Total column available from 1989 onwards • Error budget dominated by the uncertainty affecting the CF4 spectroscopic parameters • Continuous increase (+35% over 1989-2012), but with two regimes Derived global emissions:15.8 ± 1.3 Gg/yr over 1989-1997 11.1 ± 0.2 Gg/yr over 1998-2012 In very good agreement with evaluations based on AGAGE measurements

10. Carbon tetrafluoride – CF4 • Good agreement with in situ, balloon and satellite data, when accounting for the uncertainties affecting the data sets and for the time needed for CF4 to propagate and mix throughout the atmosphere • Anthropogenic contribution larger than the natural background since about the late 90s Mahieu et al., accepted for publication in AMT, 2013

11. End of WP1

12. WP2 results – VOCs Development of a retrieval strategy for methanol (CH3OH) from Jungfraujoch

13. Methanol – Finalized retrieval strategy Mahieu et al., 2012 Rinsland et al., 2009 992 – 998.7 cm-1 + Atmospheric Chemistry Experiment, 2011 995.5 – 1008.3 cm-1 Stavrakou et al., 2011 1029 – 1037 cm-1 Simulations for Jungfraujoch, 80°, 6.1 mK using HITRAN08

14. Methanol – Finalized retrieval strategy Mahieu et al., 2012 Rinsland et al., 2009 + Atmospheric Chemistry Experiment, 2011 Stavrakou et al., 2011 1029 - 1037 cm-1 Improvement of the DOFS from 1.5 to 1.8 992 – 1008.3 cm-1 Simulations for Jungfraujoch, 80°, 6.1 mK using HITRAN08

15. CH3OH: typical information content • DOFS ≈ 1.8 • 1st Eigen vector: tropospheric column • 2nd Eigen vector: some vertical resolution (LT & UTLS)

16. Methanol Seasonal Modulation and Variability No long-term trend over 1995-2012 Minimum : December to February Maximum : June-July Peak-to-peak amplitude : ≈130 % of the CH3OH yearly mean

17. Lower-Tropospheric mixing ratios • Intercomparison with in situ campaign-type measurements in 2005 (Empa) • Very few coincident measurement

18. UTLS Partial Columns • Intercomparison with occultation measurements by ACE-FTS (7-14 km) between 41 and 51ºN • Time period: 2004-2012

19. WP2 results – VOCs (ctd) Retrieval of formaldehyde (H2CO) from FTIR observations and comparison with MAX-DOAS and model results

20. Retrieval of formaldehyde – H2CO • Retrieval SFIT-2 algorithm (v3.91) • 6 microwindows (Vigouroux et al., Atmos. Chem. Phys., 9, 9523-9544, 2009) • Spectral resolution: 0.005 cm-1 • Spectroscopic parameters: HITRAN 2008 • Data set: 9481 solar spectra from January 2005 to April 2013 • SZA: 0° - 88° • Tikhonov type L1 regularization • A priori profile from 1980 – 2020 WACCM v.6 simulations Constraint matrixR = α L1T x L1

21. A priori profile from 1980 – 2020 WACCM simulations (v6)

22. TOTAL AVERAGING KERNEL x 0.10 • Limited information content: typical DOFS ≈ 1 • Sensitivity range: lower troposphere

23. Retrieval of formaldehyde – H2CO Individual measurements

24. Retrieval of formaldehyde – H2CO Monthly means

25. Retrieval of formaldehyde – H2CO

26. Retrieval of formaldehyde – H2CO

27. Test of HITRAN 2012… AVERAGED BIAS = -37.70%!!

28. WP2 results – CFC substitutes Definition of a retrieval strategy for HCFC-142b

29. Retrievals of HCFC-142b (CH3CClF2) • Lifetime of 18 years, GWP of 2310 • Its atmospheric content has been increasing to reach ≈ 21 ppt in 2011, with variable rates over the recent years: 1.1 ppt/yr in 2005-2008; 0.7 ppt/yr in 2009-2012, annual emissions on the order of 30-40 Gg • Four candidate windows have been evaluated, around 903, 967, 1133 and 1193 cm-1 (used for ACE-FTS retrievals) • HITRAN08 was used • For HCFC-142b, pseudolines based on Clerbaux et al. (1993) cross-sections were assumed. Since then, improved laboratory measurements have been produced by Le Bris & Strong (2009), but no pseudolines available…

30. Two very unfavorable cases… Here, strong CO2 or H2O lines prevent the retrieval of F142b from the ground…

31. “Strong” signal, but HDO and N2O… Weaker signal, but less critical interferences…

32. Simulation & fit for the 900-906 cm-1 window • Weak absorption, even at low sun (0.5% for 85°), but relatively clean window • Main interferences by HNO3 manifolds, CO2 and H2O lines • Red residuals when assuming no F142b in the atmosphere

33. Retrieval of F142b • Retrievals in the 903 and 1193 windows look reasonable, but are in disagreement (the 1193 columns are too high: interferences or inconsistent cross-sections?) • The 900-906 cm-1 microwindow was finally selected despite a very weak absorption (0.5% on average) • A time series has been produced for the Jungfraujoch, from 1990 onwards (daily mean data from 2000 onwards) • Comparison with in situ surface data (Mace Head and Jungfraujoch) shows good overall agreement (absolute values and trend)

34. Jungfraujoch time series Trends (2-σ): (1.05±0.08) 1013 molec./cm2/yr (6.5±0.5)%/yr (2000.0 as ref.)

35. WP5 – Outreach Publications, communications, assessments, archiving…

36. Long-term time series of halogenated source gases above Jungfraujoch • Time series and trends solicited for inclusion in the next WMO assessment on ozone depletion • Not shown (scale): SF6 and HCFC-142b • CCl4, CF4 and F142b thanks to AGACC-II funding!

37. AGACC-II publications & communications 2013 Peer-reviewed: • Mahieu et al., Spectrometric monitoring of atmospheric carbon tetrafluoride (CF4) above the Jungfraujoch station since 1989: evidence of continued increase but at slowing rate, accepted for publication in Atmos. Meas. Tech., 2013. Communications: • Bader et al., Evolution of methanol (CH3OH) above the Jungfraujoch station (46.5ºN): variability, seasonal modulation and long-term trend, poster at the EGU 2013 General Assembly, Vienna, 2013. • Kolonjari et al., Validation of ACE-FTS measurements of CFC-11, CFC-12 and HCFC-22 using ground-based FTIRs, poster at AGU Fall meeting, San Fransisco, 2013. • Mahieu et al., First retrievals of HCFC-142b from ground-based high-resolution FTIR solar observations: application to high-altitude Jungfraujoch spectra, poster at the EGU 2013 General Assembly, Vienna, 2013. • Mahieu et al., Overview of the geosphysical data derived from long-term FTIR monitoring at the Jungfraujoch NDACC Site (46.5ºN), poster at the 6th GEOS-Chem meeting, Harvard University, Cambridge, 2013.

38. Thank you! Including contributions from BIRA-IASB and Empa (CH) colleagues as well as from ACE-science team members (UWaterloo). Pseudolines from G.C. Toon (NASA-JPL)