Hello everyone,

At least 3 cyclic mechanisms are known for the catalytic destruction of stratospheric ozone (cf. Crutzen, Molina, Rowland and others).

In the stratosphere, it is usually considered that water vapour is photochemically broken down by incoming UVs from the sun to produce hydroxyl radicals that can potentially destroy ozone in one of the catalytic cycles.

The stratosphere with a typical 2ppm water vapour is extremely dry so that a catalytic destruction of ozone due to the hydroxyl radicals is rarely considered as far as I know.

Presumably this is also related to the fact that a large water vapour injection leads to rapid condensation and early removal  of water vapour from the troposphere. Tabazadeh and Turco (1993)  illustrated this by modelling the Pinatubo 1991 eruption and suggested that only 1% of the injected water can reach the stratosphere, if my recollection is correct.

Rose and coworkers (1995, Nature) also illustrated that ascending water-rich volcanic plumes get rapidly glaciated and Durand and coworkers (2008) determined that ice can form on abundant ash nuclei during cloud ascent. Textor and others (1998, JVGR; 2004 JGR) also developped numerical models of eruption columns accounting for microphysics and enabling to assess impacts of volcanic éruptions  upon atmospheric chemistry.

Nonetheless, 1% of water vapour or so reaching the stratosphere remains a significant perturbation for the extremely dry stratosphere, where removal mechanisms are also considerably less rapid than in the troposphere.

I am wondering if anyone may have modelled the possibility for massive ozone loss in the stratosphere from massive injection of water vapour (and tiny ice Crystal generation on very fine ash) by large volcanic eruptions in the stratosphere ?

I have a number of potentially interesting scenarios in mind:

- The Toba super-eruption injected huge amounts of water vapour in the mid-stratosphere (up to above 45km or so) and such an injection may have been sustained for several days whereas low stratosphere water vapour injections may have been sustained for weeks to months. 

Has anyone modelled potential stratospheric catalytic ozone loss from hydroxyl radicals generated above icy dust-size-ash and whether this could account for a possible near-extinction of human populations at the time as a result of this super-disaster ?

- The Deccan Trapps Lava fountains (around 65 Ma ago) are thought to have been capable of convecting volcanic gases into the lower stratosphere (Self, Rampino, Thordarson and others). Here there is also the likelihood that this is repeated regurlarly over a period of half a million years or so.

Has anyone tried to model stratospheric water vapour inejection and the possibility that the mass extinctions may have been related to catalytic destruction of stratospheric ozone by hydroxyl radicals ?

- The AD 180 Taupo ultraplinian eruption (NZ) column occurred across a large 200m deep lake.

Has anyone tried to quantify how much water may have been entrained, vaporized, and injected to the estimated 50km height region of the atmosphere ? Also with the view of assessing potential ozone destruction by hydroxyl radicals from such an end-member explosive eruption ? 

- I am also wondering if chronic water vapour degassing above high volcanoes such as Erebus in Antarctica (low tropopause) may also contribute significantly to local stratospheric ozone depletion by continuously making the lower stratosphere significantly more "wet" than usual ?

I would be grateful for any insights.

With best wishes and kind regards to all,

Gerald