This thread is interesting.

I don't really mind bad air quality days so much. It's just my eyes that turn all red and itchy. I've had to race on code orange days, and I've done some training rides on code red days. I just try to take it easy (but obviously not in the race) and soak myself often. I must have humidity if it's hot. If it's cooler, say in the low 80s or below, low humidity is so nice. However, once it gets hot, I need the humidity or else I start feeling sick and get heat exhaustion symptoms quickly. I won't be able to keep up with the soaking, because the jersey will dry too quickly. I grew up in a hot climate with high humidity, and so my body is accustomed to working hard while soaking wet. Sure, sweat evaporating cools you better, but not if you're not used to it. If it's in the 90s or above with intense sun, there'd better be 50%+ humidity for me. Without it, I start feeling like I'm not sweating at all, so my body thinks it has shut down, I guess. Then I start getting the goosebumps and feel nauseated. Not good. Riding in the evenings usually isn't much better for temperatures, and then all the bugs start coming out.