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Retrieval of formaldehyde from FTIR spectra preliminary results

Michel Kruglanski, Ann-Carine Vandaele, Martine De Mazière, Christian Hermans, Bart Dils, Gilles Hermans(*), Albéric Joos de ter Beerst(*) and Alexis Merlaud. Belgian Institute for Space aeronomy

(*)

student @ Université Libre de Bruxelles

Retrieval of formaldehyde from FTIR spectra -- preliminary results

Presentation outline

·Introduction

· Context

· H2CO retrievals

· Asimut · FTIR configuration and retrieval strategy · results for 28 spectra on April 15, 2007

·Comparison with model simulations ·Conclusion / Perspectives

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Formaldehyde

· H2CO: Source: photooxydation of biogenic and anthropogenic hydrocarbons and methane, and from incomplete combustion processes, incl. biomass burning Present in remote background air and urban polluted air Orders of magnitude of concentration: 0.2 to 10 ppb ; > 20 ppb in urban air; extremes > 100 ppb Nowadays measured from satellite (SCIAMACHY, OMI, ACE,...) need for correlative gb data · Summer 2006 ­ early 2007, at Brussels (50N, 4.5E, urban environment): preparation of FTIR campaign at Reunion Island and of MAXDOAS measurements at Jungfraujoch exploit for testing simultaneous measurements of H2CO.

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

FTIR observations of H2CO

· IR Windows (cm-1) selected for H2CO, using linefinding tool (J. Notholt)

center

2780.95 2778.29 2814.60 2812.23 2911.86 2807.16 2882.31

width

.37 .80 .72 .67 .65 .60 .56 ch4 ch4 hdo ch4 h2o hdo ch4 o3 hdo ch4 hdo hdo n2o hdo hdo n2o n2o n2o ch4 ch4 h2o n2o o3 solar solar no2 h2o solar co2 co2 h2o h2o solar solar no2 solar solar o3 o3 o3 o3 o3 * *

**

* Most appropriate at all sites ?! ** not suitable at Reunion; very appropriate at Jungfraujoch (2nd choice) ?!

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

FTIR configuration

· Bruker, IFS 120M

· Beamsplitter: CaF2 · · · · Detector: InSb Filter: NDSC 3 Scans: 5 Resolution: 0.00513 cm-1

1 0.8

0

OPD (cm)

250

· Date: April 15, 2007 · Sun intensity

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Retrieval strategy

· ASIMUT (BIRA-IASB code for atmospheric spectra retrieval)

· Accepts several observation geometries from space and ground, even combined ( use for IASI) · Raytracing + LBL Radiative Transfer + Optimal Estimation method. · RT : analytical derivation of the Jacobian · Full validation of code: in progress

Application to H2CO retrieval from ground-based spectra · First pass, 1 window: 2775.0 -- 2785.0 cm-1

· 5 parameters: baseline (cst & slope) and columns of CH4, H2O & N2O · CO2 and O3 are fixed; H2CO, HCl, etc. are neglected.

· Second pass, 2 µ-windows: 2778.2 -- 2778.6; 2780.8 -- 2781.2 cm-1

· 18 parameters: H2CO profile (14) and O3 profile (14) · baseline and CH4, H2O & N2O from previous pass

· Both µ-windows are almost water free

· CO2 is fixed; SO2, NO2, etc. are neglected

· A priori profiles: "midlatitude summer" std. atm. model

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Retrieval sample @ 8:57 UT, ZA=57.45

2775

2785

2778.2

2778.7

2780.8

2781.3

2778.2

2778.7

2780.8

2781.3

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Gain matrix and Average kernel

- +

30 30 30

20

20

20

10

10

10

0 2778.2

+ 2778.7

0 2780.8

2781.3

0 -0.5

1 km

0 0.5

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Retrieved H2CO columns

15

10 1E15 cm2

8:57

5

0

7

10

Hr UT

13

16 70

40

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Retrieved H2CO profiles

km

10

5

Bad meteo ?

0

0

1

H2CO VMR (ppb)

2

16 Time of day (UT hrs) 8 0

8:57

1 Ground level VMR (ppb)

2

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

IMAGES model: monthly profiles

Courtesy of J.-F. Müller

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

IMAGES model: April's profile vs retrievals

15

10

5

8:57

14:56

IMAGES

A priori

0 0

1

2

H2CO VMR (ppb)

Quite similar except at high altitudes

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

IMAGES model: diurnal variation

Courtesy of T. Stavrakou

Difficult to compare (Brussels = urban area)

>> Introduction >> H2CO retrievals >> Comparisons >>

Conclusion

Preliminary conclusions

· Formaldehyde from single FTIR spectra at Brussels: Yes · Almost two degrees of freedom · Most information between 0 and 2 km altitudes · Clear diurnal variation observed · To be done · Optimising retrieval: optimal resolution, altitude grid and apriori profile · Evaluating errors · Looking at other days · FTIR / MAXDOAS comparison · Making best use of combination of simultaneous FTIR and MAXDOAS observations

Retrieval of formaldehyde from FTIR spectra -- preliminary results

End.

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

MAX-DOAS: slant columns vs retrieved vert. columns

Courtesy of C. Fayt, M. Van Roozendael

Same location, same day Similar slope

>> Introduction >> H2CO retrievals >> Comparisons >> Conclusion

Retrieval overview

8:57

Two spectra rejected: 15:33 UT

(ZA=57.43) & 13:45 UT (ZA=44.79)

Formaldehyde from space

Courtesy: I. Desmedt, M. Van Roozendael, J.F. Muller

Satellite HCHO column measurements may help characterizing source of C at global and regional scales (e.g. impact of fires)

GOME HCHO, Aug. 1998 CO2, Aug. 1998

Global fire emissions inventory, Van der Werf, Global Change Biology, 9, 547-562, 2003

Formaldehyde from space ...help evaluate seasonalities and reduce uncertainties in global emissions through confrontation with three-dimensional model results

Jan-Feb-Mar

Oct-Nov-Dec

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