This paper presents ozone removal efficiencies, measured over an extended period of time, inthree different settings: a test plenum, an air handler providing outdoor air to a Class 100cleanroom, and a plenum downstream of an air handler providing outside air to a second, smallerClass 100 cleanroom. In each of these settings, the initial ozone-removal efficiencies werecomparable. After 8 years of service, the charcoal filters servicing the first cleanroom wereremoving about 60% of the ozone in the airstream. After 7 years of service, the charcoal filtersservicing the second cleanroom were removing 70% of the ozone in the airstream. After 5 yearsof continuous operation, the charcoal filters in the test plenum were removing more than 90% ofthe ozone in the airstream. These results indicate that adequately sized charcoal filters have verylong service-lives for ozone removal, provided their active sites are not compromised byaccumulated sub-micron particles.