I understand the process of UV absorption, but I am not sure about the Ozone scrubber, is it just a matter of comparison, like a blank for the final result of ozone concentration in air?
Such instruments are dual channel, with manganese peroxide used to scrub the ozone from one channel, so providing a reference zero for the other channel. The instrument can be arranged so that it switches the channels periodically too. So yes, it provides the blank you mention. If you do a google scholar or web of science search on authors M H Proffitt and R J MacLaughlin, you'll find the authoritative reference.