NOT medical advice: I'm 75 with some respiratory problems, in Chicago. I rode last week at 275 and 185, and had no problem at all--zero reaction. BUT the warning was for particulates, not ozone (ozone was about as low as usual, and I watch that one carefully, all the time, but if I followed it too carefully I'd never be able to ride), and I wore a well-fit KN95 mask, which should be more than enough for that. On the other hand, the 185 day I also walked two blocks to the store and back, no mask, and was coughing by the time I got home. I also ride with the mask in the winter since it keeps me breathing warm air and cold air can affect my lungs. It's better than a scarf and a lot tidier.
If the problem had been ozone I would not have ridden.
Last edited by mdarnton; 07-02-23 at 11:01 AM.