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96 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
oxide radical in the troposphere, most likely in the free troposphere, which would significantly impact
the background photochemistry in this sensitive environment (see 2.6.4).
Although the mentioned domains appear to be very different they have striking similarities when
halogen release and cycling are considered. This makes it feasible to address the associated research
questions in one research group to benefit from synergies. Figure 2.54 shows schematically our research
topics, making the interconnections more obvious.
Methods Our research tools are numerical models. The main model is the one-dimensional model
of the marine boundary layer MISTRA [von Glasow et al. , 2002a,b; von Glasow & Crutzen, 2004]
that treats chemical processes in the gas phase, in and on aerosol particles, and cloud droplets. The
microphysical module includes the growth of particles due to water vapor and uptake of other gases
and a two-way feedback with radiation. Aqueous phase chemistry is calculated in sulfate and sea salt
aerosol and - if a cloud is present - in cloud droplets that grew on each type of aerosol. The chemical
mechanism comprises about 170 reactions in the gas phase and 270 reactions in and on aqueous
particles for each of the four chemical bins. For some applications the model is run in Lagrangian box
model mode where the relevant meteorological parameters (temperature, relative humidity, particle
radius and liquid water content) are adjusted to the problem under investigation.
We are developing an improved microphysical/microchemical module that will allow us to make
more detailed studies of the microphysical (mainly growth) and chemical interactions of a particle
population.
Furthermore we have been using the global three-dimensional model MATCH-MPIC [Lawrence
et al. , 1999; von Kuhlmann et al. , 2003] that uses meteorological data from numerical weather
forecast reanalyses and allows to adjust the chemical mechanisms for the question in mind.
Main activities All group members actively take part in model development and application.
Polar halogen chemistry is being investigated by Matthias Piot (see 2.6.2) focusing on the effects
of various chemical and meteorological parameters for the development of ozone depletion events.
The effects of esp. organic surfactants on sea salt aerosol on particle growth and chemical processes
like uptake or scavenging of gas phase compounds is the subject of Linda Smoydzin (see 2.6.3).
Susanne Pechtl (b. Marquart) has developed and applied a parameterization for the nucleation of
new aerosol particle from iodine vapors (see 2.6.1, Pechtl et al. [2005]). Data from a field campaign
in Brittany (see C. Peters, Peters et al. [2005]) has been analysed with our model MISTRA. Together
with Roland von Glasow she participated in a field campaign off the coast of New England on Appledore
Island to collect data for the ongoing comparison and interpretation with numerical models.
Currently, we are making comparisons focusing on iodine and chlorine chemistry and the effects on
ozone and new particle formation (together with J. Stutz and O. Pikelnaya, Univ. of California, Los
Angeles, W. Keene, Univ. Virginia, A. Pszenny, Univ. New Hampshire and other participants of the
Appledore campaign). She is also developing the core routines of the new microphysical/microchemical
model.
The first global assessment of bromine chemistry in the free troposphere has been made by von
Glasow et al. [2004] (see 2.6.4), showing that potentially very large sinks for ozone and DMS have
been observed in previous studies. First comparisons with measurements are being made to help chose
which model scenario fits best in the southern hemisphere (Schofield et al., in prep.).
Effects of surface reactions on sea salt aerosol had been proposed in the literature to be of potentially
great importance for the marine sulfur cycle, model results of Roland von Glasow showed,
however, that the effects had been overestimated and are unlikely to be of importance (von Glasow
2005, in prep.).
A volcanic plume version of MISTRA was developed by Roland von Glasow and compared with
measurements at Mt. Etna (see Bobrowski). With the help of Alessandro Aiuppa (Univ. of Palermo,
Italy) several potential sets of initial plume conditions have been evaluated, showing that measurements
of BrO and SO2 columns can very easily be reproduced by the model encouraging us to use
the model to interpret the plume chemistry in this regard. The column densities of chlorine oxides,
however, could not be reproduced satisfactorily, we did manage to reduce the mismatch from four
orders of magnitude to a still very large factor of 30 (Bobrowski et al., submitted, von Glasow, in
prep.).
Colleagues from the National Institute for Water and Atmospheric Research (NIWA) in Wellington,
New Zealand, initiated a collaboration to investigate if observed seasonal variations in the δ 13 C concentrations
as measured at their baseline station at Baring Head can be explained by known chlorine
chemistry. Roland von Glasow has visited their group twice, the final model runs and a publication
are in preparation.