Stratospheric ozone intrusions during the passage of cold fronts over central Chile

Abstract

This study analyzes tropospheric column ozone variability in the southern hemisphere as a function of ozone transport from the stratosphere to the troposphere and photochemical formation. Geographically, the study area was located in the mid-latitudes in South America (33 degrees S), to the west of the Andes mountain range, in an area highly susceptible to stratospheric intrusions. Monthly ozonesonde measurements were recorded in Colina to ascertain seasonal vertical ozone distribution from the surface to the stratosphere between September 2010 and May 2012. Vertical distribution of the tropospheric ozone was measured in Talagante for fronts crossing from west to east in central Chile, during two periods in September 2014 and March 2015. These periods were significantly different in terms of the stratospheric ozone annual cycle and height of the tropopause. Our results showed rapid increases of approximately 50% in the tropospheric column ozone at time intervals shorter than 1 week. At the surface level, unusually enhanced ozone levels up to 10 parts per billion volume (ppbv) were observed during nighttime. Additionally, stratosphere-troposphere exchange (STE) preferentially occurred in spring and winter, with higher contribution during spring when the tropospheric column ozone attained its maximum concentration. These results provide valuable information regarding tropospheric ozone, a major local and global climate pollutant, to decision makers. In addition, they provide the research community with experimental data from the southern hemisphere, which helps bridge knowledge gaps in a region that has been rarely studied by national and international scientific communities.