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18 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
2.1.1 Long term measurements of reactive halogen species, trace gases and
aerosols by Multi Axis Differential Optical Absorption Spectroscopy
(MAX-DOAS)
Jessica Balbo (Udo Frieß, Ulrich Platt)
Abstract Two multi-axis DOAS instruments were set up at (1) the Global Atmospheric Watch
(GAW) site in Hohenpeissenberg, Germany, and (2) at the new SOLAS observatory on the island
of São Vicente, Cape Verde. The purpose of these long-term measurements is the investigation of
the tropospheric chemistry in polluted areas (Hohenpeissenberg) and in the remote marine boundary
layer (Cape Verde).
Figure 2.1: Mounting of Mini Max-Doas instruments on Hohenpeissenberg, Germany (left) and São
Vicente, Cape Verde (right)
Background Long-term observations of compounds
playing a key role in the atmospheric
chemistry are of great importance for the understanding
of the chemical processes occurring on
time scales ranging between minutes and years.
Anthropogenically emitted pollutants, such as
NOx and volatile organic compounds (VOCs)
have an impact on the tropospheric ozone budget
and can affect human health. On the other
hand, it is also important to study the remote
atmosphere in order to understand its chemical
behaviour in the absence of man-made emissions.
In recent years evidence has grown that halogen
compounds emitted by the ocean can have a severe
impact on the chemistry of the marine boundary
layer, and possibly also on the ozone budget and
thus climate on a global scale.
Methods and results Two multi-axis DOAS
instruments were installed with the purpose of
performing long-term measurements of atmospheric
trace gases. The first instrument has
been installed in August 2006 and is operated
in collaboration with the Deutsche Wetterdienst
at the Global Atmospheric Watch (GAW) Station
in Hohenpeissenberg, Germany (figure 2.1,
left). The GAW station is located about 60 km
south-west of Munich at an altitude of ≈ 1000 m.
Max-DOAS measurements performed at this location
will, depending on the wind direction, allow
to measure several important trace gases (NO2,
formaldehyde, nitrous acid) both in background
air and in polluted air masses originating from
Munich. The second long-term MAX-DOAS instrument
has been installed on the SOLAS observatory
on the island of São Vicente, Cape Verde
(figure 2.1, right). The main focus of these unique
measurements is the investigation of reactive halogen
chemistry in the subtropical marine boundary
layer based on measurements of BrO, IO, and possibly
OIO in a region where atmospheric measurements
are still very sparse.
Outlook/Future work The long-term measurements
in Hohenpeissenberg and on the Cape
Verde Islands are planned to be performed for
several years, allowing to investigate the tropospheric
chemistry both under polluted conditions
in central Europe and in the subtropical marine
boundary layer. The spectral analysis of the time
series from the two MAX-DOAS instruments is
currently under development and first results are
expected in early 2007.