Praise be to Allah.
Instead of using an aerosol when fasting, it is enough to use the siwaak which the Prophet (peace and blessings of Allaah be upon him) encouraged us to use. If he uses an aerosol and nothing from it reaches his throat, then that is o.k. But it should be noted that the smell that comes from the fasting person’s mouth as a result of the fast is not something to be disliked, because it is the effect of obedience to Allaah. In the hadeeth it says that “the smell from the fasting person’s mouth is better in the sight of Allaah than the fragrance of musk.”