For my purposes just seeing a rough measure is good enough. Meteorology is a highly developed science, but I guess it doesn't surprise me that the formula for AQI isn't that great. But I thought I saw it was an average over 24 hours when I was trying to figure out why PM2.5 was so much higher than I thought AQI was. Since pollution goes down outside of business hours, it would tend to be lower than PM2.5 or other measurements that have a shorter time scale.