You don't need microwaves to create NO2 and hence nitric acid, simple electrical discharges will suffice.
So if the high winds, strong wind sheer and snow can continually produce lots of ionisation then you can have a lightning factory, producing NO2/HNO3 and the swirling storm mixing the gas into an acid aerosol/mist to be encountered by the group downwind.
Now the enclosed volume of the tent will offer some limited protection to the poisonous mist outside, unless you go outside to relieve yourself... So that gives an explanation for the asymmetry of exposure. YuriD dying quite early and others having a range of orange/brown colour, YuriD being substantially darker than Zinaida for instance. One witness noted in the morgue that Rustem's face seemed normal whilst Igor's had darkened.
However the acid is landing on the outside of the tent and weakening the weave, n.b. the canvas will be proofed and should not display bleaching but the wind will be forcing acidic water deeper into the weave, i.e. into the back of the fabric.... So it starts to tear and the air inside the tent is becoming more acrid. The group is starting to panic. YuriD is coughing and wheezing. Dyatlov pushes his jacket into one of the tears to try and seal it. But another opens up, more poisonous air. Strangely it's getting warm. Then there is a big "pulse" and the inside of the tent becomes intolerable, suffocating. People escape as fast as they can, no time to collect stuff they have to get away from this location to be able to breathe. Semyon and Nicolai are elsewhere on the ridge taking photos of the light show over at Kholat. They return via a different route avoiding this mist that smells strange.