Abstract

We examine the appearance of the ozone hole over a populated area with more than 100,000 inhabitants. The largest population concentrations on the South American continent nearest the ozone hole region are Punta Arenas, Chile (53.0 degrees S, 70.9 degrees W) and Ushuaia, Argentina (54.5 degrees S, 68.0 degrees W), located close to the strait of Magallanes, opposite the Antarctic Peninsula. A special field mission was held in Punta Arenas, in September-October 1995 to investigate the vertical distribution of ozone during the appearance of the Antarctic ozone hole. Previous work has shown that the city of Punta Arenas is located at the edge of the hole area and is affected every year during a few days in the October period. The ozone trend near these locations is -0.5% per year using the yearly averages and -1.2% per year using the October means. This trend is 2 to 5 times larger than the global average. Several ozonesondes of the electrochemical concentration cell type were launched from Punta Arenas to determine the vertical distribution of ozone during ''normal'' and ''perturbed'' conditions. The ozone hole passed over Punta Arenas on October 12, 13 and 14, 1995. In addition to the sondes, which were launched once a day, ozone column amounts and UVB radiation were measured with a ground-based ozone Brewer spectrophotometer. The strongest ozone depletion over Punta Arenas in 1995 occurred on October 13, when the ozone column decreased from a ''normal'' value of about 325 Dobson Units (DU) to 200 DU; the vertical distribution of ozone on October 13 compared with October 6 shows depleted ozone roughly 50% less during hole conditions in the stratosphere. The UVB intensities have increased accordingly. The spectral ratio for October 13 to October 4 is 13 times larger at 297 nm.