Air Quality

My mom called me on the phone today to tell me that the air quality was going to be bad today between 1 and 4. First, I thought, why only between 1 and 4? If I go outside at 12 and then again at 1:30, will I be like, "Whoa! The air quality sure has deteriorated since the last time I was out here." And to be honest, I'm not even sure what air quality means. I guess it has something to do with pollution, but that seems to be the type of thing that wouldn't go away right before rush hour. Then, I thought, what a trivial thing to call me about. I mean, I could understand if it was just said in passing, but she called for the exact purpose of informing me about the air quality. Only a true air quality enthusiast would be excited by that news, and he would probably have known it anyway.