Just curious: ground-level ozone, where does that come from? How much does it take to damage a plant? I only notice ozone in the air when there are thunderstorms or if my laser printer's been working overtime, but I've never noticed black spots on the plants I keep indoors near the printer. Also isn't ozone a pretty strong oxidant, wouldn't it bleach a spot instead of turning it black?
I get black spots on some of my leaves but they seem to be caused by a mold, it's been hopelessly humid here this summer. In general my cats eat around the less-than-delectable spots no matter what the cause of the damage, or they move to a newer leaf. I have noticed that the females will lay eggs on some really crummy leaves even when relatively perfect ones are available nearby, though.
Certified Monarch Waystation #12
near Philadelphia, Pennsylvania