Southern Taiwan is suffering from O3 pollution due to intensive heavy industries and petroleum refineries there. The characteristics of O3 reservoir layers in Southern Taiwan were studied. The observed evolutions of O3 reservoir layers were divided into two stages. In the first stage, from evening to midnight, a deepened ozone reservoir layer initially formed from just above the ground to an altitude of 1000-1300 m. Then large decrease in O3 concentration occurred below 600-800 m from evening to midnight. As a result, a concentrated, elevated O3 reservoir layer formed at 800-1200 m by midnight. In the second stage, from midnight to next morning, the elevated O3 reservoir layer gradually decreased, finally reaching 500-900 m in the next mid-morning. Local circulations and nocturnal subsidence were responsible for the observed evolution. This is an abstract of a paper presented at the 103rd AWMA Annual Conference and Exhibition (Calgary, Alberta, Canada 6/22-25/2010).