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2.2. STRATOSPHERIC RESEARCH GROUP 43
2.2.5 Photolytic lifetime of stratospheric N2O5
Lena Kritten (André Butz, Marcel Dorf, Sebastian Kreycy, Cristina Prados, Ulrike Reichl, Benjamin
Simmes, Frank Weidner, Klaus Pfeilsticker)
Abstract Time-dependent profiles of atmospheric radicals were measured in the upper troposphere
and stratosphere during the first international high-altitude balloon campaign in the tropics (Teresina,
Brazil, 5.1 ◦ S, 42.9 ◦ W). The observed diurnal variation of stratospheric NO2 [Weidner et al. , 2005]
in conjunction with photochemical modelling allows to infer the photolytic lifetime of N2O5.
Altitude / km
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25
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15
11 12 13 14 15 16
T ime / UT
11 12 13 14 15 16
T ime / UT
[10
17
8 molec/cm 3 ]
Figure 2.21: Measured (left side) and modelled (right side) concentration of NO2 inferred from DOAS
scanning limb observations on the LPMA/IASI payload on June 30, 2005.
Background The amount and partitioning of
stratospheric NOx (NO, NO2 and NO3) and NOy
(NOx, N2O5, HNO3, ClONO2, HO2NO2, and
BrONO2) largely govern ozone photochemistry
in the mid-stratosphere (25-40 km). During daytime,
the tropical NOx is mainly supplied by the
photochemical decay of the nighttime reservoir
N2O5. Monitoring the diurnal variation of NO2
thus provides information on the photolytic lifetime
of N2O5.
Methods and results Within the framework
of an international measurement campaign dedicated
to the ENVISAT/SCIAMACHY validation,
three stratospheric balloon flights of the
mini-DOAS scanning limb instrument were performed
aboard the MIPAS-B, LPMA/DOAS and
IASI balloon payloads in tropical latitudes near
Teresina, Northern Brazil. During all flights the
UV/Vis spectrometer recorded spectra of sunlight
scattered near the horizon in the atmosphere.
Scanning elevation angles range between 0 ◦ and
−6 ◦ with the balloons floating around 33 km altitude.
The spectral retrieval of the obtained skylight
spectra relies on the DOAS method. Pro-
NO 2
file information is then obtained using established
inversion techniques (optimal estimation
technique) in combination with a 3-D radiative
transfer model [Weidner et al. , 2005]. The obtained
profiles of O3 and NO2 are compared to
the outputs of a 1-D photochemical model, which
was initialized with trace gas observations of the
LPMA/DOAS and MIPAS payloads. From the
observed increase of stratospheric NO2 at daytime,
current estimates for the photolysis frequency
of N2O5 can be tested.
Outlook/Future work
Check the photolytic lifetime of N2O5.
Analysis of all three balloon flights at Teresina for
UV/Vis absorbing gases such as O3, NO2, BrO,
OClO, IO, OIO, and CH2O.
Preparation of, and participation in, future measurement
campaigns (at Kiruna in April 2007 and
at Teresina in Sept. 2007).
Funding comes through ESA, BMBF, DFG,
and the European Union.
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