Just keeping this thread up to date with the relevant conversations happening on other threads.
So it would seem that there is a (very?) strong case for the NO2 theory. I've posted several links of objects or even no object at all! that are producing a plume of either black or orange "smoke" . Google image "ufo plume" or "ghost rocket" for these and more.
NO2 of course changes colour depending on temperature, getting darker as it gets hotter, more orange and more yellow as it cools down to it's boiling point of 21C - https://en.wikipedia.org/wiki/Nitrogen_dioxide
On contact with moisture NO2 slowly converts to nitric acid and this means that NO2 is poisonous for any creature that breathes air, the lungs slowly lose function as the conversion takes place. N.B in humans this happens slowly in some cases taking two days depending on the degree of exposure. Google "silo fillers disease". On contact with skin the nitric acid reacts with the keratin in the skin to turn it yellow and orange.
So the theory is that during a period of record geomagnetic storms (1958/1959) combined with ionisation from a powerful snow storm from the west, the western ridge of Kholat Syakhl demonstrated visual electro magnetic phenomena that attracted the DP group to camp nearby behind the north eastern ridge and this phenomena was photographed by Semyon, in particular the Plane 2 photo captures a large object illuminating the snow storm below it and the small section of the snow covered hill. The theory is then that they had sadly camped downwind of this area which began producing a plume of acrid NO2 which explains the sudden decision to leave the tent but stand some distance away before descending the hill to the forest lightly dressed unable to return to the tent.
And of course the above theory fits very well with the Chivruay incident. A difficult to understand decision to break camp, half of the group fell ill and found lying in a row on top of the tent 10 metres from the edge of the precipice! Clearly unable to move to a safer location? Simultaneously fell ill? And of course yellow skin. It's a strong fit for the above theory.
And then there's the photograph :-
There seems to be some very black smoke in that picture that imo isn't a dense snow cloud....
Are you talking geomagnetic storms created by solar activity? Or just aurora type storms? Or are tou talking geologically generated electric fields?
If there was a significant build of electrical charge and this charge was concentrated around a point or many many points, then there is a possibility that the charge can dissipate into the air and in doing so carry sufficient energy to cause chemical reactions and form ozone and possibly nitrogen dioxide. I have observed this effect myself using Piezo electric generators. The effect is quite interesting when observed in the dark. It creates a stream of illuminated (blue) charged particles that flow away from the point and you can smell the ozone.
If such a charge could be generated in geological structures and find a way for the charge to created ions in the air, then this could result in chemical reactions such as ozone and possibly nitrogen dioxide. It would also create a localised light show. This is suppose to have been observed during earth tremors.
It would be interesting to know what the geological make up of the area is?
I don't think the dark patch on the above photograph has anything to do with it though.