We investigated chemical and microphysical processes
in the late winter in the Antarctic lower stratosphere,
after the first chlorine activation and initial ozone depletion.
We focused on a time interval when both further chlorine activation
and ozone loss, but also chlorine deactivation, occur.
We performed a comprehensive Lagrangian analysis to
simulate the evolution of an air mass along a 10-day trajectory,
coupling a detailed microphysical box model to a chemistry
model. Model results have been compared with in situ
and remote sensing measurements of particles and ozone at
the start and end points of the trajectory, and satellite measurements
of key chemical species and clouds along it.
Different model runs have been performed to understand
the relative role of solid and liquid polar stratospheric cloud
(PSC) particles for the heterogeneous chemistry, and for the
denitrification caused by particle sedimentation. According
to model results, under the conditions investigated, ozone depletion
is not affected significantly by the presence of nitric
acid trihydrate (NAT) particles, as the observed depletion rate
can equally well be reproduced by heterogeneous chemistry
on cold liquid aerosol, with a surface area density close to
Under the conditions investigated, the impact of denitrification
is important for the abundances of chlorine reservoirs
after PSC evaporation, thus stressing the need to use appropriate
microphysical models in the simulation of chlorine deactivation.
We found that the effect of particle sedimentation
and denitrification on the amount of ozone depletion is rather
small in the case investigated. In the first part of the analyzed
period, when a PSC was present in the air mass, sedimentation
led to a smaller available particle surface area and less
chlorine activation, and thus less ozone depletion. After the
PSC evaporation, in the last 3 days of the simulation, denitrification
increases ozone loss by hampering chlorine deactivation.
EPIC Alfred Wegener Institut