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The first warning about the depletion of the ozone layer was given by NASA, from studies done between 1979 and 1986: the shield has been losing thickness and has a hole of 31 million square kilometers over Antarctica, equivalent to 15% of the area. terrestrial surface.
In February 1992, NASA identifies a second hole, this time over the North Pole reaching regions near the Arctic Circle.
In 1987, scientists identified chlorine present in chlorofluorocarbon (CFC) compounds as one of the pollutants responsible for the ozone layer.
It is used as a propellant in various types of sprays, aircraft engines, refrigeration circuits, plastic foam, porous plastic molds and trays, computer chips and solvents used by the electronics industry. With a lifespan of 75 years, it combines with oxygen, and makes up ozone molecules and forms chlorine gas.
The largest producers and consumers of CFCs live in the northern hemisphere. Developed countries manufacture on average 1 kg of CFC per person per year. In 1987 representatives from 57 countries in Canada signed the Montreal Protocol, pledging to halve CFC production by 1999. In June 1990 the agreement was ratified by the UN. It sets the phasing out of CFC production by 2010. More than 90 nations adhere to the agreement, including Brazil.
Although CFC emissions are highest in the Northern Hemisphere, it is on the South Pole that the first and largest ozone hole emerges. This is due to the circulation of air masses in the atmosphere. They circulate in overlapping layers - ranging from the poles to Ecuador at low altitude, and returning from Ecuador to the highest poles - and are able to carry pollutants thousands of miles from their place of origin.
In the Antarctic winter, from April to August, the region remains in darkness and pollutant winds spin in a circle, drawing in air masses from other parts of the earth. In September and October, sunlight returns to the region and stimulates ozone-depleting chemical reactions.
The hole is formed. In November the air arriving from other regions allows a partial recomposition of the Ozone Shield. The hole decreases in size but does not close completely.
We have acid rain, which is the burning of carbon and fossil fuels, and industrial pollutants that release sulfur dioxide and nitrogen into the atmosphere.
These gases combine with the hydrogen present in the atmosphere as water vapor. The result is acid rain: Rainwater, as well as frost, snow and fog, is charged with sulfuric acid or nitric acid. When they fall to the surface, they alter the chemical composition of soil and water, strike food chains, destroy forests and crops, attack metal structures, monuments and buildings.