Nasa Reported Record Low Levels Of Ozone Over The Arctic
NASA researchers report an unprecedented depletion of the ozone layer over the Arctic. Analysis of satellite observations shows that the ozone level reached its lowest point of 205 Dobson units on March 12, 2020.
The stratospheric ozone layer, located between 11 and 40 kilometers above the Earth's surface, absorbs harmful ultraviolet radiation that can harm plants and animals and affect people, causing cataracts, skin cancer and suppressing the immune system.
NASA, together with the US National Oceanic and Atmospheric Administration (NOAA), monitors stratospheric ozone using satellites, including the NASA Aura satellite, the NASA-NOAA Suomi satellite, and the NOAA-20 joint polar satellite system. The microwave echo sounder on Board the Aura satellite also assesses stratospheric levels of ozone-depleting chlorine.
In contrast to Antarctica, where every year in September and October during the spring in the southern hemisphere there is a real ozone "hole," in relation to the ozone layer over the Arctic, NASA researchers prefer to use the term "depletion."
For comparison, ozone levels over Antarctica usually fall to about 120 Dobson units in the spring. In the Arctic, March values sometimes drop to 240 units. Similar low levels of ozone occurred in the upper atmosphere in the stratosphere, in 1997 and 2011. But this year the record was broken.
"Such a low level of Arctic ozone as this year happens about once a decade" — Paul Newman, chief Earth science specialist at NASA's Goddard space flight Center, is quoted in a NASA press release as saying. — This concerns the overall state of the ozone layer since Arctic ozone levels are usually high in March and April."
The March depletion of the ozone layer in the Arctic, according to scientists, was caused by a combination of factors that arose from unusually weak "wave" events in the upper atmosphere from December to March. These waves control the movement of air in the upper atmosphere, similar to weather factors that we observe in the lower atmosphere, but on a much larger scale.
Typically, these waves travel up from the lower atmosphere at mid-latitudes and disrupt the circuit of circumpolar winds that circulate the Arctic. At the same time, they bring with them ozone from other parts of the stratosphere, replenishing the reservoir over the Arctic, and also contribute to heating the Arctic air. Higher temperatures create unfavorable conditions for the formation of polar stratospheric clouds that emit chlorine, which is involved in ozone-depleting reactions.
From December 2019 to March 2020, stratospheric wave phenomena were weak and did not disrupt the polar winds. Thus, the winds acted as a barrier, preventing ozone from other parts of the atmosphere from replenishing its level over the Arctic. In addition, the stratosphere remained cold, resulting in the formation of polar stratospheric clouds that allowed chemical reactions to release reactive forms of chlorine, such as chlorofluorocarbons, and cause depletion of the ozone layer.
Recall that the use of chlorofluorocarbons in the industry was banned in the late 1980s, the Montreal Protocol on substances that Deplete the ozone layer.
"We don't know what caused the weak wave dynamics this year," Newman said. — But we know that if we hadn't stopped releasing chlorofluorocarbons into the atmosphere because of the Montreal Protocol, the depletion of Arctic ozone resources this year would have been much worse."