The ozone hole is large, but it is mitigated by CFC reductions
The ozone hole is large, but it is mitigated by CFC reductions
the hole in the ozone layer that is formed over Antarctica every September and October was slightly higher than the average size in 2018, but smaller than expected for climatic conditions. Temperatures lower than the average in the Antarctic stratosphere created the ideal conditions to destroy ozone, said scientists at NASA and NOAA, but the decrease in the levels of ozone depleting chemicals prevented the hole from growing as much as it does 20 years.
"Chlorine levels in the Antarctic stratosphere have dropped about 11 percent since the peak year," said Paul A. Newman, chief scientist of Earth Sciences at NASA's Goddard Space Flight Center. "The cooler temperatures this year would have given us a much larger ozone hole if the chlorine was still at the levels we saw in the year 2000."
The ozone hole reached an average area of 22.9 square kilometers (8.8 million square miles) in 2018, almost three times the size of the contiguous United States. It is ranked 13th out of 40 years of NASA satellite observations.
The maps on this page show the state of the ozone hole on the day of its maximum depth; that is, the day on which the lowest concentrations of ozone were measured in those years. The maps at the top of this page show 2000 and 2018, when the ozone concentrations were 89 Dobson units and 102 Dobson units, respectively. The next series shows the day of Minimum concentration in each year. since 1979 (except 1995, when data were not available).
Stratospheric ozone is measured in units of Dobson (DU), the number of molecules needed to create a pure ozone layer of 0.01 millimeters thick at a temperature of 0 degrees Celsius and an air pressure of 1 atmosphere (the pressure in the Earth's surface) . The average amount of ozone in the Earth's atmosphere is 300 Dobson units, equivalent to a layer of 3 millimeters (0.12 inches) in thickness, approximately the height of 2 cents stacked together.
The ozone hole in 2018 was strongly influenced by a stable and cold Antarctic vortex, the stratospheric low-pressure system that flows clockwise into the atmosphere over the continent. These colder conditions, among the coldest since 1979, helped support the formation of more polar stratospheric clouds. The particles in such clouds activate forms of chlorine and bromine that destroy the ozone layer in the stratosphere.
The ozone hole was quite large in 2018 due to the cold conditions, but less severe than it could have been in previous decades. The difference is a long-term reduction of ozone-depleting substances (such as chlorofluorocarbons or CFCs) that were eliminated from commercial production by Montreal Protocol. Atmospheric levels of CFCs and similar compounds increased until the year 2000, but have slowly decreased since then.
The chemicals that deplete the ozone layer in the air are abundant enough to cause significant losses. According to NOAA scientist Bryan Johnson, conditions in 2018 allowed significant ozone removal in a deep layer of 5 kilometers (3.1 miles) above the South Pole. The South Pole saw a minimum of ozone of 104 Dobson units on October 12, which makes it the 12th lowest year of the 33 years of Ozone measurements where (balloon) at the pole.
"Even with the optimal conditions this year, the ozone loss was less severe in the higher altitude layers," Johnson said, "which is what we would expect given the decrease in chlorine concentrations we are seeing in the stratosphere."
Images from the NASA Earth Observatory by Joshua Stevens, using data courtesy of Ozone clock from NASA. Edited by Mike Carlowicz using a story by Ellen Gray, the Earth Science News Team at NASA, and Theo Stein, National Oceanic and Atmospheric Administration.
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