Data Set Description: --------------------- PI: Florence GOUTAIL SAOZ UV-Visible Spectrometer Site(s): BAURU 22.347 S 49.027 W 640 m Measurement Quantities: O3, NO2 Contact Information: -------------------- Name: Florence GOUTAIL Address: Service d'Aeronomie du CNRS, BP n¡3, 91371 Verrieres le Buisson, France Phone: 33 (0)1 64 47 42 89 FAX: 33 (0)1 69 20 29 99 Email: florence.goutail@aerov.jussieu.fr Reference Articles: ------------------- Pommereau, J.P. and F. Goutail, O3 and NO2 Ground-Based Measurements by Visible Spectrometry during Arctic Winter and Spring 1988, Geophys. Res. Lett., 891, 1988. Pommereau, J.P. and F. Goutail, Stratospheric O3 and NO2 Observations at the Southern Polar Circle in Summer and Fall 1988, Geophys. Res. Lett., 895, 1988. Hofmann, D.,J., P. Bonasoni, M. De Maziere, F. Evangelisti, A. Sarkissian, G. Giovanelli, A. Goldman, F. Goutail, J. Harder, R. Jakoubek, P. Johnston, J. Kerr, T. McElroy, R. McKenzie, G. Mount, J. P. Pommereau, P. Simon, S. Solomon, J. Stutz, A. Thomas, M. Van Roozendael, E. Wu, Intercomparison of UV/Visible Spectrometers for measurements of Stratospheric NO2 for the Network for the Detection of Stratospheric Change, J. Geophys. Res., 16, 765-16, 791, 1995. Vaughan G., H. K Roscoe, L.M. Bartlett, F.M. O'Connor, A. Sarkissian, M. Van Roozendael, J-C. Lambert, P. C. Simon, K. Karlsen, B. A. Kaastad Hoiskar, D. J. Fish, R. L. Jones, R. Freshwater, J-P. Pommereau, F. Goutail, S. B. Andersen, D. G. Drew, P. A. Hughes, D. Moore, J. Mellqvist, E. Hegels, T. Klupfel, F. Erle, K. Pfeilsticker, and U. Platt, An intercomparison of ground-based UV- visible sensors of Ozone and NO2, J. Geophys. Res., 102, 1411-1422, 1997. Goutail, F., J-P. Pommereau, C. Phillips, C. Deniel, A. Sarkissian, F. Lefevre, E. Kyro, M. Rummukainen, P. Ericksen, S.B. Andersen, B-A Kaastadt Hoiskar, G. Braathen, V. Dorokhov and V.U. Khattatov, Ozone depletion in the Arctic during the winters 1993-94 and 1994-95, J. Atm. Chem., 32, 281-314, 1999. Pfeilsticker, K. , Arlander, D. W. , Burrows, J. P. , Erle, F. , Gil, M., Goutail, F. , Hermans, C. , Lambert, J.-C. , Platt, U. , Pommereau, J.-P. , Richter, A. , Sarkissian, A. , Van Roozendael, M. ,Wagner, T. , Winterrath, Intercomparison of the influence of tropospheric clouds on UV-visible absorptions detected during the NDSC intercomparison campaign at OHP in June 1996, Geophys Res Lett., 26 / 8 , 1169, 1999 Lambert, J.C., Van Roozendael, M., Simon, P.C., Pommereau, J.P., Goutail, F., Gleason, J.F., Andersen, S.B., Arlander, D.W., Buivan, N.A., Claude, H., De La Noe, J., De Maziere, M., Dorokhov, V., Eriksen, P., Green, A., Karlsen Tornqvist, K., Kastadt Hoiskar, B.A., Kyro, E., Leveau, J., Merienne, M.F., Milinevsky, G., Roscoe, H.K., Sarkissian, A., Shanklin, J.D., Staehelin, J., Wahlstrom Tellefsen, C. and Vaughan, G., , Combined characterization of GOME and TOMS total ozone measurements from space using ground-based observations from the NDSC, Adv. Space Res., 26, 1931-1940, 2001. Instrument Description: ----------------------- The SAOZ is made of a commercial Jobin-Yvon CP200 flat field spectrometer equipped with a holographic grating and a Hamamatsu diode array uncooled detector, with an entrance slit allowing an average resolution of the order of 1 nm in the range 300-600 nm. They are two options: one is using a 200 gr/mm grating associated to a 512 diode array detector and a 25 micron entrance slit and the other is using a 360 gr/mm grating associated to a 1024 diode array detector and a 50 micron entrance slit allowing a better oversampling (2 instead of 1). The equipment which is ran in the outside, is placed in a dust-and-water proof container on the top of which a quartz window is mounted in order to look at the zenith sky with a total field of view of 10¡. The instrument is driven by a computer which records and analyses the spectra in real time. Measurements are performed from sunrise to sunset until a Solar Zenith Angle (SZA) of 94deg. The exposure time is adjusted automatically between 0.1s to 60s in order to optimize the signal and the spectra are co-added in memory during a 60s duty cycle. The dark current is measured each time the duration of exposure changes and subtracted. Averages of ozone and NO2 morning and evening vertical columns measured between 86 and 91 SZA are calculated and transmitted in real time to the laboratory through the ARGOS satellite data collection system or through INTERNET. Columns transmitted to NDSC data bank are reprocessed data, only possible after original spectra are received at the laboratory from the remote stations. Algorithm Description: ---------------------- The spectral analysis is described below. After a precise wavelength alignment with the use of the Fraunhofer solar absorption lines, actual spectra are divided by a reference spectrum recorded at high sun on a clear and unpolluted day. Monotonic large trends are then removed by subtracting the same spectrum smoothed at a broad bandpass (40 nm) resulting in an atmospheric differential spectrum, into which narrow features corresponding to absorption by ozone, nitrogen dioxide, O4 (oxygen dimer), water vapour, O2 and OClO, are remaining. Slant columns are then calculated by least squares fitting between the signal and the differential cross sections of each absorber in an iterative process in which the contributions of the various species are calculated and removed sequentially. Ozone is measured in the Chappuis visible bands (450-620 nm) where the cross sections are independent of the temperature; nitrogen dioxide in 410-530 nm range; O4 in two bands (465-484 nm and 556-584 nm); H2O in one band (440-600 nm)and O2 around 630nm. Expected Precision/Accuracy of Instrument: ------------------------------------------ Converting slant columns relative to a given reference spectrum into vertical columns requires the knowledge of the optical path of the light scattered at zenith, that is the Air Mass Factor (AMF) and the residual amount of constituent still present in the reference spectrum. The AMF is calculated by modelling the radiative transfer of the sunlight into the atmosphere. In the visible at 500 nm, the average atmospheric scattering layer at 90 SZA is located around 10-12 km, that is below the ozone and nitrogen dioxide peak concentration and above tropospheric clouds. The AMF in use in Real Time are the " Standard SAOZ AMF " identical for all stations and all seasons. At 90deg SZA they are respectively 16.59 for ozone and 17.77 for NO2. Here, for the NDSC re-processing, we are using O3 tropical AMF calculated from annual average composite profiles from SAGE II V6 + MOSAIC + SAOZ balloon sonde and for NO2 tropical AMF calculated from average summer evening composite profiles from HALOE V19 + SAOZ long duration balloon sonde. The AMF is calculated at the centered wavelength of the fitting band: at 525 nm for O3 and 470 nm for NO2(In the case of the old 512 pixels instrument the O3 AMF is calculated at 510 nm). At 90deg SZA the "Tropical" AMF are respectively 16.3 for ozone and 14.3 for NO2. The residual amount of constituent present in the reference spectrum is determined by a Bouguer-Langley plot (slant column versus AMF) extrapolated to zero air mass.They are respectively: 6.5e+18 and 5e+15 for ozone and NO2 for the first period (1995-2000). They are respectively: 4e+18 and 8e+15 for ozone and NO2 for the second period (2001-). The precision of the total column measurements at twilight (86 - 91 SZA) is 2 Dobson Unit for ozone and 1.5 10+14 mol/cm2 for NO2. The accuracy, including uncertainties of cross-sections and their temperature dependencies and that of Air Mass Factors (vertical profiles of the constituent, stratospheric temperature seasonal changes and photochemical changes for NO2) is: ± 4% for ozone (2% cross sections and 2% AMF) and 10% for NO2 (5% cross sections, 5% AMF). Instrument History: ---------- -------- starting date: 1995/11/21 spectrometer: Jobin Yvon CP200, grating: 200 gr/mm, 300-600nm, FWMH: 0.7nm detector: NMOS, 512 pixel entrance slit: 25 microns instrument nb:1 Analysis sofware: SAM V5 starting date: 2001/02/06 spectrometer: Jobin Yvon CP200, grating: 360 gr/mm, 270-630nm, FWMH: 0.9nm detector: NMOS, 1024 pixel entrance slit: 50 microns instrument nb:1 Analysis sofware: SAM V5