Measurements
of Antarctic ozone and polar stratospheric cloud profiles in a time of
decreasing atmospheric chlorine,
climate change, and fluctuations in polar vortex strength
National Science Foundation,
$885,472, April 2009 - April 2011, PI:
T. Deshler, CoI: J. Mercer, Location:
McMurdo Station,
Antarctica Submitted: 6
June 2008
In the final twenty years of the last century there was
a rapid decline in Antarctic stratospheric ozone in austral spring
resulting
from the halogens released into the atmosphere since the 1930s. In the
austral
polar stratosphere temperatures often dip below -80ºC, cold enough
to form
stratospheric clouds. The particles in these clouds provide surfaces
upon which
halogen bearing molecules interact, thereby converting inactive
chlorine into a
photo-labile species. Rapid, chlorine
induced, catalytic conversion of ozone to diatomic oxygen then occurs
as
sunlight returns in austral spring. The resulting ozone loss reached
unprecedented minimums in the late 1990s as stratospheric chlorine
peaked.
Ozone profile measurements during this period indicated 4-6 km vertical
regions
in the mid to lower stratosphere devoid of ozone. The dangers of
halogen
releases were published in the 1970s, 20 years after atmospheric
releases of
halogens became common. The dangers were confirmed in the mid 1980s and
the
first controls on halogen release were established with the Montreal protocol
in 1987. This protocol,
with its amendments, has significantly reduced halogen releases.
Records suggest
that stratospheric chlorine reached its maximum in the austral
stratosphere in
the late 1990s, early 2000s. Currently stratospheric chlorine may be
near 1995
levels with a faster than anticipated reduction. The response of ozone
to these
initial decreases in chlorine was anticipated to be minimal, since the
halogen
maximum had saturated ozone loss chemistry. Any of a number of
measurements of
ozone do not confirm these expectations. In 5 of the last 7 years ozone
has
remained well above the minimums observed in the late 1990s. While
these
results may be controlled primarily by variations in stratospheric
dynamics and
temperature, there is an anticipation that the first signs of ozone
recovery
may be clear soon.
We propose here to continue in situ balloonborne
ozonesonde measurements through 2011. These
ozone measurements, begun in 1986, documented the decline and minimum
in ozone
observed as chlorine increased and reached its maximum. The recent
measurements
show that most recent years (except for 2006) have not suffered as
severe an
ozone loss as in the late 1990s. The emphasis now is on maintaining the
measurements required to observe the first
signs of ozone recovery.
Ozonesondes are uniquely
capable of observing in the altitude range suffering the greatest
chemical
loss, and thus able to separate chemical and transport effects. Thus
these instruments
may be among the first to establish the ozone benefits resulting from
declining
chlorine. We will also continue laboratory investigations of the
chemistry
within electrochemical cell ozonesondes to establish a transfer
function for
data sets which include measurements with different ozonesondes and
different solution
strengths. This supports our WMO and NDACC involvement to establish
recommendations for ozonesonde operating procedures.
Polar stratospheric cloud (PSC) observations will be
continued with new instrumentation to address questions related to the
nucleation of nitric acid hydrates and the existence of large particles
within
Antarctic PSCs. For these measurements we will continue collaborating
with Dr. Marcel Snels, Institute of Atmospheric
Sciences and Climate of the National Research Council, Rome, on the
lidar
measurements from McMurdo, which help guide our PSC measurements.
The intellectual merit of this work lies in
obtaining and analyzing measurements which may lead to the first signs
of ozone
recovery, clarifying the electrochemistry occurring in ozonesondes,
investigating
the nucleation of nitric acid hydrate particles, and documenting the
existence
of large PSC particles in the Antarctic.
The broader impacts include maintaining measurements
which may help establish the first signs of ozone recovery, an
important
reassurance to the world community in support of the commercial
sacrifices
required to limit the release of chlorine into the atmosphere. Thus, in
addition to the scientific interest, there are broad social
implications
dependent on maintaining ozone measurements through the first decade
after
maximum chlorine has been reached in the stratosphere. This research
contributes to the training and education of a research scientist,
engineer,
technician, and graduate students. Three of the eight members of my
group are
women thus increasing the contribution of underrepresented groups in
science.