In 1960 A W Brewer developed his mast ozonesonde for measuring the ozone in the stratosphere. The device was heavier than the lightweight instruments carried in balloons to investigate the physical characteristics of the upper air. It therefore required a larger balloon than used before to reach the stratosphere, which is above the layers of the atmosphere normally studied in this way. This instrument was used in the European Arctic Stratospheric Ozone Experiment in 1992, during which scientists established that the amount of ozone in the northern stratosphere was decreasing.
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