A new spectroscopic observatory in Créteil to measure atmospheric trace gases in solar occultation geometry

C. Viatte, P. Chelin, M. Eremenko, C. Keim, J.-M. Flaud, J. Orphal, M. RayLaboratoire Inter-Universitaire des Systèmes Atmosphériques (LISA), CNRS, Universités de Paris 12 (Paris-Est) et Paris 7, 61 Av. du Général de Gaulle, 94010 Créteil, France.

ABSTRACTGround-based Fourier Transform Infrared (FTIR) and Ultraviolet (UV) spectroscopy based on solar occultation is a powerful remote sensing technique to determine vertical distribution of various constituents in the atmosphere [1]. In this context, a new spectroscopic observatory (with motorised dome rotation) was installed on the roof of the University of Paris 12 in Créteil. It comprises a solar tracker (Bruker Ltd.) coupled with two spectrometers operating in different spectral regions, to obtain information on various atmospheric target species such as H 2O, O3, CO, CH4, N2O, NO2, HNO3, H2CO, C2H6, PAN etc. and the most abundant isotopic species. We have first characterized the ILS (Instrumental Line Shape) width of the FTIR at about 0.06cm-1 using CO absorption lines in a low pressure cell. The second step was to determine a set of micro-windows for O3 in the infrared region that are appropriate for retrievals of vertical concentration profiles taking into account the limited spectral resolution of our instrument.The experimental data, in particular concerning the free troposphere, will be compared to predictions from an atmospheric chemistry model (CHIMERE) developed at LISA in order to improve its results, and also to satellite observations (IASI in particular) for validation. In addition, retrievals of the same trace gases combining data in different spectral regions will be attempted.

Experimental setup Instrumental Line Shape

set of micro-windows in IR for O3

References : [1] C. Senten et al;Technical Note: New ground-Based FTIR measurements at Ile de La Réunion : observations, error analysis, and comparisons with independent data, Atmos. Chem. Phys. Discuss. 8, 827-891, 2008 [2] F. Hase et al: Intercomparison of retrieval codes used for the analysis of high-resolution, ground-based FTIR measurements, J. Quant. Spectrosc. Rad. Transf. 87,

25-52, 2004

IR : A Fourier Transform spectrometer (Bruker Vertex 80) is used for the infrared region 400 15000 cm-1 with a maximum spectral resolution of about 0.05 cm-1.UV-VIS : A grating spectrometer with a CDD array (Ocean Optics, HR 2000+) is used with 1.1 nm resolution (FWHM, sampling 0.035 nm) and covers the spectral range of 1901100 nm.

To select the IR MW’s of O3 appropriate for the retrieval, we check the spectral region which has the larger variability according to a change of concentration (vmr) (from 10 to 30 %) in the troposphere and in the stratosphere using PROFFIT [2] (ground-based radiative transfer and retrieval model)

First Results

1) 780-790 cm-1

2) 970-1150 cm-1

3) 2000-2140 cm-1

4) 2730-2820 cm-1

5) 3000-3100 cm-1

Conclusions

FTIR

Solar tracker

Motorised dome rotationSet up

1) The new experimental set-up is now fully operational at LISA Créteil.2) We will use H2O and O3 to validate precision and accuracy of the new

set-up. 3) Then we will validate satellite (IASI) and meteorological (ECMWF)

H2O and O3 data.4) We aim to improve knowledge of free tropospheric composition

above Paris (VOCs)

FWHM = 0.06 cm-1

UV-VIS : main characteristics (07-28-08 at 11.00 am)

2040 2070 2100 2130 2160 2190 2220 2250

1.45

1.50

1.55

1.60

1.65

1.70

1.75

sig

na

l

wavenumber (cm-1)

CO

grating spectrometer with optical fiber silicon CCD array 2048 pixels Integration time 86 ms

2150.88 2150.96 2151.04 2151.12 2151.20 2151.28 2151.36

1.46

1.48

1.50

1.52

1.54

1.56

1.58

1.60

1.62

1.64

1.66

sig

nal

wavenumber (cm-1)

CO

6400 6600 6800 7000 7200 7400 7600 7800 8000

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

sig

nal

wavenumber (cm-1)

CH4

2046 2048 2050 2052 2054 2056 2058 2060 2062-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

sig

na

l

wavenumber (cm-1)

CO

2740 2750 2760 2770 2780 2790 2800 2810 2820 2830

0.00

0.05

0.10

0.15

0.20

0.25

0.30

sig

na

l

wavenumber (cm-1)

N2O

3110 3120 3130 3140 3150 3160 3170 3180 3190

0.00

0.05

0.10

0.15

0.20

0.25

sig

nal

wavenumber (cm-1)

H2O

4760 4780 4800 4820 4840 4860 4880 4900 4920-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

sig

na

l

wavenumber (cm-1)

CO2

780 782 784 786 788 7902750000

2800000

2850000

2900000

2950000

3000000

3050000

3100000

3150000

sig

na

l

wavenumber (cm-1)

MW 1

960 980 1000 1020 1040 1060 1080 1100 1120 1140 1160

0

2000000

4000000

6000000

8000000

10000000

sig

na

l

wavenumber (cm-1)

MW 2

1980 2000 2020 2040 2060 2080 2100 2120 2140 2160

8000000

10000000

12000000

14000000

16000000

18000000

20000000

22000000

sig

na

l

wavenumber (cm-1)

MW 3

2720 2730 2740 2750 2760 2770 2780 2790 2800 2810 2820 2830

25000000

26000000

27000000

28000000

29000000

30000000

31000000

sig

na

l

wavenumber (cm-1)

MW 4

2990 3000 3010 3020 3030 3040 3050 3060 3070 3080 3090 3100 3110

24000000

26000000

28000000

30000000

32000000

34000000

36000000

sig

na

l

wavenumber (cm-1)

MW 5

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

0

7000000

14000000

21000000

28000000

35000000

sig

na

l

wavenumber (cm-1)

MW 1 MW 2 MW 3 MW 4 MW 5

300 400 500 600 700 800 900 10000

2000

4000

6000

8000

10000

12000

14000

16000

18000

sig

na

l

wavelength (nm)

Band A of O2

2000 4000 6000 8000 10000 12000 14000

0.0

0.1

0.2

0.3

0.4

tra

nsm

issi

on

wavenumber (cm-1)

ATMOSPHERIC SPECTRA

IR: main characteristics (07-22-08 at 16.08 pm) OPD : 8.4 cm 1.5 mm aperture DTGS detector 100 scans (32 min) CaF2 beamsplitter