Atmospheric NO from space: the SCIAMACHY capabilities

Phys. Chem Earth (C). Vol. 26,No.l, pp. 545-548,2001 0 2001

Elsevier Science Ltd. All rights reserved 1464-1917/01/%- see front matter

Pergamon

PII: Sl464-l9l7(Ol)OOO44-7

Atmospheric C.Muller, Belgian

NO from Space: The Sciamachy Capabilities

J. C. Lambert, C. Lippens and M. Van Roozendael

Institute for Space Aeronomy, Avenue Circulaire,

3, B-l 180 Brussels, Belgium

Received 25 April 2000; accepted 27 February 2001

Abstract. The Scanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY (SCIAMACHY) has been proposed in 1988 as a payload of the ESA earth observation satellite ENVISAT 1, which is scheduled for launch in 2001 for a four-year mission. SCIAMACHY operates in eight channels covering the UV, the visible and two infrared regions. Recent developments in the testing of the instrument now enable not only the full use of channel .l (240 nm-314 nm) at a required high level of performance but in some special cases its extension to 220 nm. This instrumental improvement allows new objectives to be addressed in the upper stratosphere, on top of the already proposed mesospheric and thermospheric investigations of nitric oxide. Simulations show the instrument capabilities for these studies. These NO observations will be performed in solar occultation, lunar occultation and nadir. Previous NO results are reviewed with an emphasis on results obtained by the infrared solar occultation technique as exemplified by the SPACELAB grille spectrometer and other instruments. The capabilities of SCIAMACHY for mapping the total column of upper atmospheric NO is investigated as well as possibilities to infer NO vertical distribution and transfer properties between the different atmospheric regions.0 2001 Elsevier Science Ltd. All rights reserved

1. ENVISAT objectives. The ESA ENVISAT satellite is now (March 2001) scheduled for a launch in July 2001, the satellite and payload are undergoing integrated tests in the ESA ESTEC facilities in the Netherlands. Three instruments that have the study of atmospheric chemistry as their main objective are: the stellar occultation U.V.-visible instrument: GOMOS, the thermal infrared sounder: MIPAS and SCIAMACHY. SCIAMACHY (Burrows et al, 1988) was proposed to ESA as part of the first ENVISAT payload. It was accepted by ESA as an “Announcement of opportunity” instrument for the ENVISAT payload. SCIAMACHY is now a cooperative programme of Germany, the Netherlands and Belgium. The primary objective of SCIAMACHY is to determine vertical and horizontal distributions of important atmospheric constituents and parameters (ozone and other trace species, aerosols, radiance, irradiance, clouds, Correspondence

to: C. Muller

temperature and pressure) from measurements of radiance combining scattered, absorbed and reflected light from the and Earth’s surface. Radiance Earth’s atmosphere measurements will be performed in different viewing geometries: nadir, limb and solar and lunar occultation. These measurements will contribute to the better understanding of major climate and environmental issues: Tropospheric pollution including industrial emission and biomass burning Troposphere/stratosphere exchange processes Stratospheric ozone chemistry Climate change - chemistry interactions Volcanic eruptions Solar variability. The two other instruments aim at similar objectives, centred on the zones where an active biosphere interacts with the atmosphere.

2. Nitric oxide vertical distribution Nitric oxide has relevance in all atmospheric zones: in the troposphere, where it is a direct pollutant and a precursor of tropospheric ozone; in the stratosphere where it contributes to the ozone layer equilibrium and finally in the upper mesosphere and thermosphere where its photo ionisation by the solar Lyman a radiation leads to the formation of the ionosphere and thus influences radio Nicolet and propagation (Nicolet, 1945, 1965, Thermospheric NO was measured by its Aikeu1960). resonant fluorescent emissions in the y and 6 bands by rocket and space means since the middle of the sixties (Barth, 1964) by rocket and space borne instruments, its relation to solar activity was rapidly put into evidence, however, below 80 km, Rayleigh scattering dominates the NO emission and thus this technique did not bring any information on the NO situation in the stratosphere and mesosphere. The urgent necessity of proving the presence of nitrogen oxides in the natural stratosphere led to its first determinations in infrared solar occultation from balloons and high altitude aircrafts (Ackerman et al, 1973). This observation programme was continued from space by the SPACELAB payloads: ESA Grille and NASA ATMOS leading to the distribution shown on figure 1 (Laurent et al, 1985, Gunson and Irion, 2000).

546

C. Muller et al.: Atmospheric

NO from Space

1973 and which was used by the Grille spectrometer for its determination from SPACELAB 1 in 1983 (Laurent et al, 1985). GOMOS and SCIAMACHY have to rely on the nitric oxide y bands to access NO, unfortunately, the GOMOS spectral range begins only at 250 nm while the nominal SCIAMACHY range begins only at 240 nm, leaving out the more intense bands all situated between 200 and 230 nm.

Fig. 1: Observed nitric oxide (concentration in molec/cm3 versus altitude in km.) Comparison of the November 1983 Spacelab 1 Grille spectrometer result with the ATLAS 3 ATh4OS results obtained in similar conditions above the Southern polar regions, the ATh4OS results are from version 3 (Gunson and hion, 2000) and the grille results are from Laurent et al (1988) with supplemental points above 95 km originating from a solar CO spectrum obtained during the same solar occultation.

Figure 1 shows the main features of the NO distribution: a stratospheric maximum, a minimum at the stratopause and extremely variable conditions above 100 km, the maximum at the tropopause in the ATMOS data (Gunson and Irion, 2000) is still under investigation by the ATMOS team. Similar profiles in infrared occultation were obtained by the HALOE instrument on board UARS and confirm these findings despite a larger error for the thermospheric mesospheric part (Russell. et al, 1993) The infrared emission limb sounder CRISTA (covered essentially the upper part of the mesospheric distribution as well as the limb UV sounders: MAHRSI (Stevens et al, 1997), IS0 (Torr et al, 1995), SME and SNOE (Barth et al, 1999). The NO distribution reaches now the thirty years of high quality observations. However, three areas of insufficient coverage and accuracy can be identified: the troposphere, the upper stratosphere where the value of the NO minimum is actually not known as all remote sensing techniques are influenced by the lower and upper maximums and finally, despite all the existing work, the thermospheric part where small spatial scale variations seem to appear. Diurnal variations vary also considerably with altitude, from almost instantaneous equilibrium with NO, in the stratosphere to lifetimes of the order of one day in the thermosphere. Long term variations of the stratospheric maximum and its spatial distribution are, of among the nominal ENVISAT atmospheric course, objectives. 3. ENVISAT

and SCIAMACHY

capabilities.

At ENVISAT proposal time, MIPAS was the only payload instrument covering a specific spectral NO interval: the 5.3 pm infrared fundamental band which has several uncontaminated lines including the 1914.993 cm-l doublet in which it was first observed in the stratosphere in

The MIPAS observation will require careful retrieval in order to separate the stratospheric part from the much warmer thermospheric emissions, observations in the cold upper troposphere and lower stratosphere will probably prove to be extremely difficult. Stratospheric NO disappears entirely at night while thermospheric NO has a the measurement of diurnal much longer lifetime, variations in this range is one of the objectives of a specific ENVISAT observation proposals (Muller et al, 1999). However, MIPAS covers the v3 NOz band and as well as HNOs bands and will thus be able to perform’ perfectly its stratospheric NOy monitoring objective. As GOMOS and SCIAMACHY were by design excellent NO2 monitors in their visible range, the original spectral range did not include a possibility for NO During SCIAMACHY testing, the measurement. verification and suppression of straylight in the 240-300 nm range let to check the quality of the 218 to 240 nm corresponding to unused pixels of the detector. This interval is especially important because it includes the NO y band centred at 226 nm, which has high absorption by the non-excited nitric oxide and thus allows its observation in the stratosphere and troposphere. Unfortunately, atmospheric scattering prevents the use of this interval in the troposphere by any means except long path DOAS (Reisinger, 1999, cross-sections shown on fig.2), in the stratosphere, the surest way to assess NO signal will be by solar occultation where signal reappears already weakly at 40 km. of altitude to become comfortable above 50 km, the stratospheric NO maximum around 40 km of altitude would give a 20% absorption if the best spectral resolution is attained in flight ( fig 3.). This altitude region is a region of very low signal due to important Rayleigh absorption, but in the case of the SCIAMACHY instrument, an extensive testing of detectors will allow at least to give a try to stratospheric UV occultation measurements. The UV would be far more efficient for the study of the presently little known upper part of the NO stratospheric distribution between 50 and 60 km of altitude. With previous tecliniques, this region was often below the threshold of detection and thus the transport of NO between atmospheric regions could never have been put in evidence by observation. At higher altitude, in the mesosphere, a second maximum reappears between 80 and 120 km of altitude and is much easier to detect as NO is distributed among the upper level states and appears thus also in other bands which can then be detected in the nominal channel 1 range of SCIAMACHY, this mesospheric and thermospheric study is the subject of

C. Muller et al.:

specific A.O. proposals relating studies (Muller et al, 1999).

to airglow

Limtptransmisqion50, 60,95 km

NO: slant columns

AtmosphericNO from Space

and aurora1

I

of

1.~16andl.el7

-

50km

-

60km

-

65km

-I

0.6

0.4

0.2 w

0.0 200

I

I

I

I

210

220

230

240

541

band and could not be used below the stratopause, it is also slightly outside the possible SCIAMACHY instrumental range. As the entire gamma bands are included in the observed feature, pressure and temperature dependence can be neglected in a first approximation and the obtained slant columns can then be fitted to determine a vertical distribution of NO in the upper stratosphere and lower mesosphere. An alternate technique will involve the use of a full line-by-line retrieval and will be performed as a second step. The use of the limb emission data outside occultations will depend on the actual performance of the instrument in flight. The extension of the observation range to the 226 nm range is now included in SCIAMACHY nominal operations. This allows in the limb mode a global mapping of NO from the upper stratosphere to the thermosphere using a technique similar to the one described for occultation. SCIAMACHY has also a lunar occultation capability. This nighttime measurement will provide important information on the thermospheric NO absorptions and emissions and the way they perturb the observation of daytime stratospheric NO.

wavelength (nm)

Fig. 2: Modtrau 3-7 computation, the 50 km curve still receive significant signal due to the design backscattered radiation. with the cross-sections private communication,

I

1.0

T

;./ /‘!i JT I

I-

I

..___ _ 1

(

0.6

s ._

of the instrument which allows the detection of The transmission spectrum of NO is generated used in long path NO monitoring (Reisiuger, 1999).

’

Od

f

0.4

0.2

2

0.0

224

22s

226

227

wavcnumber(“In,

Fig. 3: spectrum of the y 1-O bands of NO computed for an optical path of 1.E 16 molecules of NO and for a temperature of 220 K, the resolution of Icm-I is 15 times better than the nominal SCIAMACHY resolution. The molecular data is derived from Steven (1995). This line by line simulation, when reduced in resolution confirms the results deduced from the data of Reisiuger (1999) as to the baud position, the actual SCIAMACHY resolution will be determined in flight in view of the observed signal in these critical regions of the upper stratosphere.

The interpretation of solar occultation will be based on the determination of slant columns using either the cross-section used in figure 2 (Reisinger, 1998, 1999) or more elaborate line by line determinations derived, for example, from the spectroscopic data used by Stevens (1995), a line by line simulation confirms the potential for occultation of the 226 nm and 215 nm bands (fig.3), unfortunately, the slightly more intense 215 nm band is even more affected by Rayleigh scattering than the 226 nm

The nadir data presents a more complicated problem; abundant thermospheric NO can be produced on small spatial and temporal scales by different energy deposition mechanisms ranging from solar flares to intrusions of magnetospheric filaments. This NO content will completely mask the lower altitudes both in absorption and in emission. This NO emission has been successfully observed during the SSBUV flights (MC Peters, 1989) and has shown to be related to various aspects of solar activity. Its modelling is important for the main SCIAMACHY objectives as this operation can improve the accuracy of the ozone retrieval algorithms. Due to the intensity of the thermospheric emissions, it is not hoped that accurate stratospheric columns will ever be determined by this technique; however, the thermospheric column will be retrieved using modelling techniques similar to the ones used by MC Peters (1989). This observation was also successively performed during the GOME flight but the necessity of integrating over several spectra and thus losing spatial resolution makes it difficult to use (Fig. 4), it is hoped that better performance of SCIAMACHY in this spectral range will allow to reduce the integration requirement and to enable a spatial mapping of these emissions. 4. Conclusions. While being able to continue and develop observations already well begun by SSBUV and a series of limb sounders exemplified by SME, SCIAMACHY will be original in its solar occultation mode by providing the upper part of the stratospheric maximum and the value of the minimum preceding the mesospheric-thermospheric maximum. This vertical distribution will determine from observational data if any nitric oxide can be transported from the mesosphere to the stratosphere or even, if any stratospheric in-situ source of nitrogen oxides could exist. The analysis of this profile will thus confirm or infirm the thirty years old theory (Crutzen, 1970) assigning the

C. Muller et al.: Atmospheric

548

photodissociation of nitrous oxide originating from the troposphere as the main stratospheric NOx source, in this respect, the NO study with SCIAMACHY fully fits the ENVISAT basic objectives.

-

NO gamma

bands deteded

in GOME

spedra

0.3

0.2

0.1

0.0

-0.1 210

220

230

240

250

260

270

280

290

wavelength (nm)

Fig. 4: Average over 54 nadir GOME spectra showing the position of they bands of NO present in the channel 1 spectra1 interval, these emissions originate in the lower thermosphere.

Acknowledgments: This work is part of the Belgian SCIAMACHY preparation program financed through PRODEX by the OSTC. (Federal office of science , technology and cultural policy)

References Ackerman, M., Frimout, D., Muller, C., Nevejans, D., Fontanella, J.C., Girard, A. and Louisnard, N., Stratospheric nitric oxide from infrared spectra, Nature, 245, 205-206, 1973. Barth, CA., Rocket measurements of the nitric oxide dayglow, J. GeophysRes., 69,3301-3303, 1964. Burrows J. P., K. V. Chance, P. J. Crutzen, H. van Dop, J. C. Geary, T. J. Johnson, G. W. Harris, 1. S. A. Isaksen, G. K. Moortgat, C. Muller, D. Pemer, U. Platt, J.-P. Pommereau, H. Rodhe, E. Roeckner, W. Schneider,

NO from Space

P. Simon, H. Sundqvist, and J. Vercheval 1988 “SCIAMACHY - A European proposal for atmospheric remote sensing from the ESA Polar Published by Max-Planck-lnstitut fur Chemie, 55 122 Mainz, Platform” Germany, July 1988. Barth, C.A., Bailey, S.M.,and Solomon, S.C., Solar-terrestrial salar soft x-rays coupling: and thermospheric nitric oxide, Geophys.Res.Let., 26, 125 1- 1254, 1999. Crutzen, P.J., The influence of nitrogen oxides on the atmospheric ozone content, Quart.J. Roy. Met. Sot., 96, 320-325, 1970. Kaufmann, M. and Vollmann,K., Thermospheric Grossmann,K.U., Nitric Oxide Infrared Emissions Measured by CRISTA , Adv. Space Res. vo1.19, pp. 591-594, 1997. Gunson,M.R., Irion,F.W. ATMOS version 3, Jet Propulsion Laboratory, Pasadena, California, http://remos.ipl.nasa.oov/atmosversion3/atmosversion3.html ,200O. Laurent, J., Lemaltre, M.P., Besson, J., Girard,A., Lippens,C., Muller,C., Vercheva1.J. and Ackerman,M., Middle atmospheric NO and NO2 observed by the SPACELAB-I grille spectrometer, NATURE, 315, 126-127, 1985. MC. Peters, Climatology of nitric oxide in the upper stratosphere, mesosphere and thermosphere : 1979 through 1986, J. GeophysRes., 94, 3461-3472, 1989. Muller, C., I. Aben, W.J. van der Zande and W.Ubachs, Uses of the ENVISAT payload for mesospheric and thermospheric investigations: the AALlM proposal, in Proc. European Symposium on Atmospheric Measurements from Space (ESAMS), ESA/ESTEC, The Netherlands, 1821 January 1999, ESA WPP-161, Vol. 2, 623-626, 1999. Nicolet, M., Contribution a l’etude de I’ionosphere, Mtm. Mus. Hist. Nat. Belg., 19, l24pp, 1945. Nicolet, M., Ionospheric processes and nitric oxide, J. Geophys. Res., 70,691-701, 1965. Nicolet , M. and Aiken, A.C., The formation of the region D of the ionosphere, J. Geophys. Res., 65, 1469-1483, 1960. Reisinger, A.R.; Fraser, G.J.; Johnston, P.V.; McKenzie, R.L.; Matthews, W.A. Slow-scanning DOAS system for urban air pollution monitoring. In: Proceedings of the XVIII Quadrennial Ozone Symposium, 959-962. Bojkov, R.D.; Visconti, G. (eds.) Parco Scientific0 e Technologico d’Abruzzio, L’Aquila, Italy, 1998. Reisinger, A.R., private communication, 1999. Russell, J. M. III, L. L. Gordley, J. H. Park, S. R. Drayson, D. H. Hesketh, R. J. Cicerone, A. F. Tuck, J. E. Frederick, J. E. Harries, and P. J. Crutzen: ‘Ihe Halogen Occultation Experiment, J. Geophys. Res., 98, 10.777-10.797, 1993. data available at : http://haloedata.larc.nasa.gov Stevens, M.H., Nitric oxide y band fluorescent scattering and self absorption in the mesosphere and lower thermosphere, J. GeophysRes., 100, 14735-14742, 1995. Stevens, M.H., R.R. Conway, J.G. Cardon, J.M. Russell III, MAHRSI Observations of Nitric Oxide in the Mesosphere and Lower Thermosphere, Geophys. Res. Let., 24,3213-3216, 1997. Torr, M.R., Torr, D.G., Chang, T., Richards, P., Swift, W. and Li, N., Thermospheric nitric oxide from the ATLAS 1 and Spacelab 1 missions, J. Geophys. Res., 100, 17389-17413, 1995.