As we used to say in dispatch, there's an FAR for that....
§ 121.578 Cabin ozone concentration.
(a) For the purpose of this section, the following definitions apply:
(1) Flight segment means scheduled nonstop flight time between two airports.
(2) Sea level equivalent refers to conditions of 25 °C and 760 millimeters of mercury pressure.
(b) Except as provided in paragraphs (d) and (e) of this section, no certificate holder may operate an airplane above the following flight levels unless it is successfully demonstrated to the Administrator that the concentration of ozone inside the cabin will not exceed -
(1) For flight above flight level 320, 0.25 parts per million by volume, sea level equivalent, at any time above that flight level; and
(2) For flight above flight level 270, 0.1 parts per million by volume, sea level equivalent, time-weighted average for each flight segment that exceeds 4 hours and includes flight above that flight level. (For this purpose, the amount of ozone below flight level 180 is considered to be zero.)
(c) Compliance with this section must be shown by analysis or tests, based on either airplane operational procedures and performance limitations or the certificate holder's operations. The analysis or tests must show either of the following:
(1) Atmospheric ozone statistics indicate, with a statistical confidence of at least 84%, that at the altitudes and locations at which the airplane will be operated cabin ozone concentrations will not exceed the limits prescribed by paragraph (b) of this section.
(2) The airplane ventilation system including any ozone control equipment, will maintain cabin ozone concentrations at or below the limits prescribed by paragraph (b) of this section.
(d) A certificate holder may obtain an authorization to deviate from the requirements of paragraph (b) of this section, by an amendment to its operations specifications, if -
(1) It shows that due to circumstances beyond its control or to unreasonable economic burden it cannot comply for a specified period of time; and
(2) It has submitted a plan acceptable to the Administrator to effect compliance to the extent possible.
(e) A certificate holder need not comply with the requirements of paragraph (b) of this section for an aircraft -
(1) When the only persons carried are flight crewmembers and persons listed in § 121.583;
(2) If the aircraft is scheduled for retirement before January 1, 1985; or
(3) If the aircraft is scheduled for re-engining under the provisions of subpart E of part 91, until it is re-engined.
[Doc. No. 121-154, 45 FR 3883, Jan. 21, 1980. Redesignated by Amdt. 121-162, 45 FR 46739, July 10, 1980, and amended by Amdt. 121-181, 47 FR 58489, Dec. 30, 1982; Amdt. 121-251, 60 FR 65935, Dec. 20, 1995]
https://www.law.cornell.edu/cfr/text/14/121.578It's almost exclusively associated with colder than normal air masses and low tropopause heights so not a problem 3 seasons out of the year. I looked to see if there was a map of the southern hemisphere that would show a concentration but I don't see any upper air temps that would be so cold, or tropopause heights so low as to allow the ozone layer to dip into the 30-40 thousand foot range. It almost has to be what has become known as a "polar vortex" over the lower 48 of the United States to affect domestic traffic. The last few years I was dispatching it was more common than the first few years. The farthest south I remember seeing it on a map where it had to be avoided was the Ohio river on the Illinois Indiana State line down to about FL340. That was during a really cold winter around 2014-2015. But there were plenty of times spots over the northern border states had areas to be avoided.
I can't speak to all airlines but generally narrow bodies of all types, up to 757's do not have ozone scrubbers since the problem isn't encountered often enough to make them worthwhile. Wide bodies do as they are generally capable of flying more northerly and polar routes where you can expect to find large dips of ozone all winter long.
What's the point of an open door policy if inside the open door sits a closed mind?