OBSERVATIONS OF THE 1995 OZONE HOLE OVER PUNTA-ARENAS, CHILE

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 Punt a Arenas, Chile (53.0 degrees S, 70.9 degrees W) and Ushuaia, Argentin a (54.5 degrees S, 68.0 degrees W), located close to the strait of Mag allanes, opposite the Antarctic Peninsula. A special field mission was held in Punta Arenas, in September-October 1995 to investigate the ve rtical distribution of ozone during the appearance of the Antarctic oz one hole. Previous work has shown that the city of Punta Arenas is loc ated 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 i s -0.5% per year using the yearly averages and -1.2% per year using th e October means. This trend is 2 to 5 times larger than the global ave rage. Several ozonesondes of the electrochemical concentration cell ty pe were launched from Punta Arenas to determine the vertical distribut ion of ozone during ''normal'' and ''perturbed'' conditions. The ozone hole passed over Punta Arenas on October 12, 13 and 14, 1995. In addi tion to the sondes, which were launched once a day, ozone column amoun ts and UVB radiation were measured with a ground-based ozone Brewer sp ectrophotometer. The strongest ozone depletion over Punta Arenas in 19 95 occurred on October 13, when the ozone column decreased from a ''no rmal'' value of about 325 Dobson Units (DU) to 200 DU; the vertical di stribution of ozone on October 13 compared with October 6 shows deplet ed 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.