Abstract: Embodiments of the present invention relate to an apparatus for detecting ozone in ambient air, including an absorption cell with a bounded chamber for receiving air sample for analysis, a light source positioned to transmit light through absorption cell, a detector positioned to measure the attenuation of light passing through absorption cell, a pumping system for transporting ambient air into chamber and then reversing direction to transport ozone-free air into the absorption cell for purging the chamber, a scrubber positioned downstream from outlet port of the absorption cell to remove ozone from sample air exiting the absorption cell, a relative humidity (RH) equalizer for controlling humidity of sample air exiting absorption cell such that the sample entering scrubber has relatively the same humidity as ambient air, and a data system for digitizing and processing output from detector.