I found something under "My Account >> Unit Measurements".
The last item on the list is Air Quality Index :: USA :: Edit
Follow the "Edit" link and it will take you to the pop-up page showing a variety of locations and an explanation off to the right. You can scroll through it.
From this, I don't think that there is a sensor, rather a look-up for the data. So far, it doesn't seem to be active.
Greg H.