The weather forecast said that today would be the hottest day of the heat wave, with temperatures expected to climb up to ninety-five degrees: just the kind of fall weather in which temperature inversions form. Sure enough, as I drove across the San Mateo Bridge this morning, I realized the air closest to the ground had a definite yellowish tinge; above a certain altitude, about a thousand feet there was an abrupt transition from that yellowish color to no color at all. The heat and sunlight was creating smog, and a temperature inversion was keeping the smog from dispersing upwards. My throat has felt a little raw since the hot weather, and the attendant temperature inversions, began two days ago, and now I could see the cause of the rawness: the nasty yellow-tinged smog I was breathing in.