8 research outputs found
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Distribution of halon-1211 in the upper troposphere and lower stratosphere and the 1994 total bromine budget
Satellite confirmation of the dominance of chlorofluorocarbons in the global stratospheric chlorine budget
OBSERVED increases in concentrations of chlorine in the stratosphere1-7 have been widely implicated in the depletion of lower-stratospheric ozone over the past two decades8-14. The present concentration of stratospheric chlorine is more than five times that expected from known natural 'background' emissions from the oceans and biomass burning15-18, and the balance has been estimated to be dominantly anthropogenic in origin, primarily due to the breakdown products of chlorofluorocarbons (CFCs)19,20. But despite the wealth of scientific data linking chlorofluorocarbon emissions to the observed chlorine increases, the political sensitivity of the ozone-depletion issue has generated a re-examination of the evidence21,22. Here we report a four-year global time series of satellite observations of hydrogen chloride (HCl) and hydrogen fluoride (HF) in the stratosphere, which shows conclusively that chlorofluorocarbon releases - rather than other anthropogenic or natural emissions - are responsible for the recent global increases in stratospheric chlorine concentrations. Moreover, all but a few per cent of observed stratospheric chlorine amounts can be accounted for by known natural and anthropogenic tropospheric emissions. Altogether, these results implicate the chlorofluorocarbon s beyond reasonable doubt as dominating ozone depletion in the lower stratosphere
Stratospheric aerosol evolution after Pinatubo simulated with a coupled size-resolved aerosol–chemistry–climate model, SOCOL-AERv1.0
We evaluate how the coupled aerosol–chemistry–
climate model SOCOL-AERv1.0 represents the influence of
the 1991 eruption of Mt. Pinatubo on stratospheric aerosol
properties and atmospheric state. The aerosol module is coupled
to the radiative and chemical modules and includes comprehensive
sulfur chemistry and microphysics, in which the
particle size distribution is represented by 40 size bins with
radii spanning from 0.39 nm to 3.2 µm. SOCOL-AER simulations
are compared with satellite and in situ measurements
of aerosol parameters, temperature reanalyses, and ozone observations.
In addition to the reference model configuration,
we performed series of sensitivity experiments looking at different
processes affecting the aerosol layer. An accurate sedimentation
scheme is found to be essential to prevent particles
from diffusing too rapidly to high and low altitudes. The
aerosol radiative feedback and the use of a nudged quasibiennial
oscillation help to keep aerosol in the tropics and
significantly affect the evolution of the stratospheric aerosol
burden, which improves the agreement with observed aerosol
mass distributions. The inclusion of van der Waals forces in
the particle coagulation scheme suggests improvements in
particle effective radius, although other parameters (such as
aerosol longevity) deteriorate. Modification of the Pinatubo
sulfur emission rate also improves some aerosol parameters,
while it worsens others compared to observations. Observations
themselves are highly uncertain and render it difficult
to conclusively judge the necessity of further model
reconfiguration. The model revealed problems in reproducing
aerosol sizes above 25 km and also in capturing certain
features of the ozone response. Besides this, our results
show that SOCOL-AER is capable of predicting the most important
global-scale atmospheric effects following volcanic
eruptions, which is also a prerequisite for an improved understanding
of solar geoengineering effects from sulfur injections
to the stratospher
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