[DSSM]

In grape/raisin production, dusting sulfur is applied to the foliage to suppress powdery mildew. The sulfur is usually applied using equipment as in the picture below. The sulfur is not treated heated by any means. Is there any chance that any of this could be converted into sulfur dioxide during application? Or is more likely that it could be found by means of improper testing? Temperature in the region can reach above 110°F.



http://ag.wilburellis.com/Products/Product%20Documents/PlantProtectLABELS/Wilbur-Ellis%20Dusting%20Sulfur_F-081313.pdf

[Arkcon]

So its not heated, it just happens to be sometimes at 44 °C.  Not really much difference beyond semantics.     Ok, so is there sulfur dioxide contamination -- that I don't don't know.  Unless you mean a trace?  Some noxious things are very detectible by humans senses, SO₂ is one of those.  Certainly a large pile of powdered sulfur has a acrid scent, which is probably SO₂.  I don't know if its significant for health, or even if its detectable in your average air sample.  You'll have to tell us more about what you're looking for.

[DSSM]

The concern of sulfur dioxide has more to with residue on the fruit. We had a customer say that their lab results came back showing sulfur dioxide being present at about 45 PPM. We are trying to determine what the cause of the residue could be since regular raisins are not treated with sulfur dioxide, only sulfur in its solid form.

[Arkcon]

OK, 45 ppm is not a trivial amount, that doesn't sound to me like something accidental.  Deliberately burning sulfur in air will generate a great deal of SO₂ and that has been used as a fumigant -- in storage places, in empty wine barrels, or even it deliberately exposing cut fruit to prevent browning when the fruit is dried.  Don't know if its accidental or a contamination in your case.