Solar Power Generation Going Down

There were no clouds in the sky today, but my solar system only generated 49 Kwh, down from a peak a few weeks ago of 52+ Kwh. The lower production might be related to shorter days and dust on the cells. We haven't had rain for a week or so, and dust could be a problem. Also, the ozone level is high, but I don't know if that affects the solar energy reaching my house.