SO3 is an acid anhydride gas.
It would function in this case as an oxidizing agent just
as the ozone does.
It's a whole lot easier to get and the 'acid` smell functions
as a safety warning so you don't breath it in for too long.
I believe the toxicity is higher than the ozone, (the gas goes
into solution on the moist surfaces in your lungs, O3 produces
hydrogen peroxide, SO3 - sulfuric acid), but the amount in
question would be small and the exposure short.

MadDog