Relationship between the ozone and water vapour vertical profiles on Mars observed by NOMAD-TGO
Arianna Piccialli, A. C. Vandaele, Royal Belgian Institute for Space Aeronomy, Belgium, S. Aoki, Graduate
School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan, F. Daerden, Y. Willame, C. Depiesse,
L. Trompet, L. Neary, S. Viscardy, J. Erwin, I. R. Thomas, B. Ristic, Royal Belgian Institute for Space
Aeronomy, Belgium, J.P. Mason, M.R. Patel, School of Physical Sciences, The Open University, Milton
Keynes, U.K., A. Khayat, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; Center for Research and Exploration in Space Science and Technology II, University of Maryland, USA; M. Wolff, Space
Science Institute, Boulder, CO, USA, G. Bellucci, Istituto di Astrofisica e Planetologia Spaziali, IAPS-INAF,
Rome, Italy, J.-J. Lopez-Moreno, Instituto de Astrofisica de Andalucia, IAA-CSIC, Granada, Spain.

Introduction:
Recently, [1] characterized the relation between
ozone and water vapor using SPICAM simultaneous
measurements of O3 and H2O column densities covering four Martian years. They found that O3 and
H2O columns are clearly anti-correlated at high latitudes while being uncorrelated at low latitudes.
In our study, we take advantage of the NOMAD
capability to measure simultaneous vertical profiles
of ozone and water vapor to characterize the O3 –
H2O relationship at different altitude ranges and latitudes.
Ozone and water vapor profile retrievals:
NOMAD (Nadir and Occultation for MArs Discovery) is a spectrometer composed of 3 channels: 1)
a solar occultation channel (SO) operating in the
infrared (2.3-4.3 μm); 2) a second infrared channel
LNO (2.3-3.8 μm) capable of doing nadir, as well as
solar occultation and limb; and 3) an ultraviolet/visible channel UVIS (200-650 nm) that can work
in the three observation modes [2,3].
The UVIS channel has a spectral resolution <1.5
nm. In the solar occultation mode it is mainly devoted to study the climatology of ozone and aerosols
content [4, 8]. NOMAD-UVIS spectra are simulated
using the line-by-line radiative transfer code
ASIMUT-ALVL developed at IASB-BIRA [5] using
the Optimal Estimation Method to derive the local
density profile in one go (on all transmittances of one
occultation observation).
Water vapor was observed by the infrared channel of the NOMAD SO. The results from a first
analysis can be found in [6], while an extended dataset is presented in a companion abstract [7]. Water
vapor and ozone are measured simultaneously, which
allows us to investigate the water-ozone correlation,
the key to address the atmospheric chemistry on
Mars.
The O3-H2O relationship:
We present correlation plots of O3 vs. H2O at
high latitudes (60°-90°, both hemispheres), and at the
equator (30°S-30°N). It is important to notice that
during a solar occultation experiment at the termina-

tor, ozone may exhibit rapid changes due to photolysis that are uncorrelated to water vapor. As an example, we show the 60°N-90°N latitude region (Figure
1): a clear anti-correlation is observed at lower altitudes, up to 40 km. O3 is roughly proportional to
(H2O)-1.0 up to 30 km and a variation with Ls seems
also present.

Figure 1: O3 (cm-3) vs. H2O (cm-3) vertical profiles
measured simultaneously by NOMAD-UVIS at high
latitudes in the Northern hemisphere (60°N-90°N).
(a) 10 – 20 km; (b) 20 – 30 km; (c) 30 – 40 km; (d)
40 – 50 km. Colours indicate the Ls interval. The
black line shows the function O3 =H2Ox, with x varying with the altitude range.
References:
[1]
Lefèvre,
F.
et
al.
10.1029/2021JE006838. [2] Vandaele, A.C., et al.,
Planetary and Space Science, Vol. 119, pp. 233–249,
2015. [3] Neefs, E., et al., Applied Optics, Vol. 54
(28), pp. 8494-8520, 2015. [4] Patel et al. (2021) [5]
Vandaele, A.C., et al., JGR, 2008. 113
doi:10.1029/2008JE003140. [6] Aoki et al., 2019,
Journal of Geophysical Research, Volume124, Issue12, Pg. 3482-3497, doi:10.1029/2019JE006109
[7] Aoki et al., Europlanet Science Congress 2021,
ID EPSC2021-153 [8] Khayat et al. 2021, DOI
10.1029/2021JE006834.