Being poorly known, the ion chemistry of the lower stratosphere is generally ignored, or treated as similar to that of the middle atmosphere, by the current chemistry-climate modes. Some recent achievements in atmospheric chemistry have motivated us to re-asses the ionization efficiency of galactic cosmic rays (GCR) and ion-molecular reaction initiated by them. We reveal that near to the maximum of the GCR absorption, the energetically allowed ionmolecular reactions form an autocatalytic cycle for continuous O 3 production in the lower stratosphere. The amount of the produced ozone is comparable to the values of the standard winter time O 3 profile. This is an indication that GCR are responsible for a greater part of the lower stratospheric ozone variability then is assumed currently.
Recent
experiments with chemistry–climate models reveal
that local ozone production at extratropical latitudes dominates its
transportation from the tropics (The
origin of ozoneGreweV.
Grewe, V.
Atmos. Chem. Phys.2006614951511), which contradicts
the popular idea that tropical photochemistry is the principle source
of stratospheric O3. Analysis of the efficiency of photochemical
reactions beneath the peak of the ozone layer shows that they could
hardly be the main source of O3, especially at winter high
latitudes. In this paper, I show that ion–molecular reactions,
launched in the layer of secondary electrons, itself generated near
the tropopause by galactic cosmic rays (GCR), could serve as a local
source of ozone at middle to high latitudes. Careful inspection of
the efficiency of the reactions reveals that an extremely dry atmosphere
above the tropopause favors the production of the short-lived tetraoxygen
ion O4
+, whose dissociation activates an autocatalytic
production of ozone. My modeling calculations show that the electron
impact production of O3 is comparable to its climatological
density near the maximum of the free electron layer. Moreover, statistical
analysis of the connectivity between GCR and ozone at 70 hPa divulges
the hemispherical asymmetry of the O3 response to GCR forcing.
This asymmetrical response is attributed to the hemispherically asymmetric
geomagnetic field, which controls the depth of penetration in the
atmosphere as well as the intensity and spatial distribution of precipitating
charged particles in the Earth’s atmosphere. The heterogeneously
distributed energetic particles and the ion–molecular reaction
triggered by them could explain the well-established hemispherical
and longitudinal asymmetry in the spatial distribution of ozone.
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