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Free keywords:
ozone; aerosol heterogeneous chemistry; nonlinear system; multiequilibrium; catastrophe
Abstract:
The impact of odd chlorine (Cly) and odd nitrogen (NOy) perturbations (resulting from
human activities) and of enhanced H2O-H2SO4 aerosol load (associated with volcanic
activity) on stratospheric ozone (25 km altitude, midlatitudes) is assessed by using a
chemical box model in which key heterogeneous reactions on the surface of sulfate aerosol
particles are taken into account. The model shows that if transport is ignored, the response
of the photochemical system to increased abundances of odd chlorine and odd nitrogen
and to enhanced aerosol surface area density is characterized by a multiequilibrium
regime. Catastrophic transitions may occur and may produce dramatic reductions in the
stratospheric ozone concentration. When the dissipative effects associated with transport
are taken into account, the system still exhibits a nonlinear response to external nitrogen
and chlorine sources but without multiequilibrium solutions or catastrophic transitions.
Over a sensitive interval, small external disturbances applied to model parameters can lead
to large changes in the state of the system. For example, the large drop in ozone derived by
the model when dissipative transport effects are taken into account corresponds to a
degeneracy of the multiequilibrium regime found when dissipative terms are
omitted.
