During the southern spring, a break of the polar vortex over the Antarctic continent frequently occurs. This results in the advection of ozone-poor air mass (O3) to mid-latitudes, characterizing the secondary effect of the Antarctic ozone hole (SEAOH). We present some distinct characteristics the eight greatest reductions of the total O3 column (TOC) over the central region of Rio Grande do Sul (RS, 29.5°S, 54°W), southern Brazil, between August and November from 2012 to 2016 and develop a full scalar diagnostic index of O3 negative anomalies for South America. For developing the index, mean values of the absolute potential vorticity, geopotential height, and wind components were obtained over moving grids with positive and negative O3 anomalies. It was then possible to develop statistical methods to obtain a diagnostic index of the SEAOH (Subantarctic O3 Index), as well as a diagnostic index of incursions of ozone-poor air masses from the tropics (Subtropical O3 Index). The results show that TOC over the central region of RS, for the most intense O3 reduction episodes, is governed by a wide range of contributions from high and low isentropic levels. Significant interaction of air masses of polar and tropical origin via stratosphere–troposphere exchange was found. Finally, the Subantarctic O3 Index combined with the Subtropical O3 Index showed potential use for prediction centres and was skilful in detecting regions with the most negative O3 anomalies, mainly in the mid-latitude region, but also in the subtropical region.