We have "Ozone alert days", here, quite often, because of our topography and the heat. Ours are rated green (good air day)yellow, orange(unhealthy for sensitive groups), red, and purple (nobody should breathe outdoors <img src="i/expressions/face-icon-small-wink.gif" border="0"> ). I may have to revise that after I go back and check, but basically, that's it. Reds are rare, and I have never seen a purple.
I has something to do with the ozone, but this is a ground level ozone, not "hole in the ozone layer" alert. It has to do with the quality of the air you are breathing. For example, when the wildfires in Georgia were blowing over here on us, we had yellow ozone alerts in the times when the smoke was thinner, and red when it was really bad. It does make a difference in how I feel if I spend a lot of time outside during these alert days.
If you have alert days, I would heed them. It really is about the effects of the "bad air" on your lungs and heart <img src="i/expressions/face-icon-small-wink.gif" border="0"> .
Oh, and we just got our "blinky boards" on the highways/interstates (took them 5 years I think to get them up and running right *rolls eyes* and about the only thing we see on them are the ozone warnings and forcasts for the next day. It is kinda aggravating to be stuck in traffic, looking at a bilboard that is telling you "Ozone Alert- reduce driving" instead of telling you where the traffic tie-ups are and why you are sitting in traffic! lol <img src="i/expressions/face-icon-small-wink.gif" border="0">