Looks to be most likely greasy spot; a better guess could be made if you post a photo of the underside of the leaf. I would say it could be edema; but that is almost exclusively found in indoor container plants.

John, here is the underside. Thanks!

Nope, don't think it is greasy spot fungus. Maybe an infestation of spider mites; take a close look with a 10X loupe. Still could be citrus edema (you can google it); but it is not common in outdoor plants.

Well I definitely have some mite issues going on. Looked at the leaves under my printer's loupe and saw very small, white (maybe clear) mites. Didn't see any webbing, so can't tell exactly what type of mites they are. I sprayed with Spinosad about a week ago but apparently it didn't do the trick. I'll see if there may be a "catch all' spray or oil to use.

Neem oil works better for mites. Just don't use it on days when the air temps are going to be 85*F or more. And you may need to treat a few times over a few weeks to get stragglers. Be sure to follow the label.

Spinosad works better on chewing type insects, so not so good for mites or aphid.