[theBCnut]

If it’s the wind, I’m thinking more along the lines of pollen or mold irritation, rather than a particle. That sort of irritation can last for days. If he’s pawing at it, it is irritating him. You might want to get some eye wash and use it.

Why not just seal up the current food and go ahead and change to the next one, then if it clears up, change back again and see if it comes back. That way you will know absolutely that it’s the food, or not.