I just returned from about 3 days of shooting at night when the temperatures would start around 50 F and would drop to 18 F leaving a frost on the ground. The lens hood did a decent job acting as a dew/frost protector, unfortunately over 4 night various portions of my 14mm lens ended up with bits of frost on the lens. Wherever a bit of frost attached itself to the lens it left a stain that does not seem to be affected by rubbing with a microfiber cloth and there are hundreds of these stains on my lens, each about 0.1 or 0.2 cm in diameter. Has anyone else experienced the same phenomena and does anyone know how you are supposed to remove these stains?
It sounds like you need to do wet cleaning. Use some lens cleaner fluid and either a lens tissue or a fine microfiber cloth to clean the surface of the lens' front element. Be sure to follow instructions provided with your lens cleaning fluid and apply a few drops of cleaner to the tissue/cloth before wiping the lens rather than applying the cleaner directly to the glass. Doing the latter will likely cause streaking and also may increase the risk of wet cleaner getting inside the lens, where it can leave deposits!
Wet cleaning will remove the deposits of dust that were present and were more or less glued to the surface of the lens by the moisture from the frost. Trying to remove such dried on deposits using dry cleaning methods such a dry microfiber cloth can damage the coatings on the lens.
Sounds like this are leftovers from water condensation. Try a few rounds of breathe-and-wipe cleaning with reasonably firm pressure and the stains should go away. Lens coatings these days are pretty durable and I don't think that they are destroyed by 18F temperature.