Looks like hard water to me, atleast from the image. I had hard water spots from out sprinkler system, used chemical guys heavy duty water spot remover. Worked like magic.
Definitely looks like a mix of hard water and dirty road water.. like everyone else said, try a 50/50 mix of water and vinegar and it should clear up all of the hard water spots. Look into a spray on ceramic wax to help keep things clean.