Why does the ozone layer deplete faster in winter months over the poles?

Why is the depletion of the ozone layer greater in the winter months over polar regions?


Is it because there is more release of $\ce{NO\_x}$ due to the increased use of fossil fuels in heating which depletes the $\ce{O3}$ layer?




As mentioned in the comments, "polar vortex" is one of the prime reason ozone layer depletes faster in winter months over the poles. This is beautifully explained here [1]:



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> Under normal conditions, the amount of stratospheric ozone depends on the amount of sunlight reaching a certain geographic area of the atmosphere. The seasonal variation is low in low latitudes because sunlight is fairly constant year-round. In high latitudes, sunlight goes way down in the winter months. Ozone typically "builds up" to higher values over the poles during the winter and early spring in each hemisphere. Because this season is offset by 6 months in the Northern and Southern hemispheres, the effect is seen at the North and South poles roughly 6 months apart.
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> [...] The air masses above the poles become isolated from the rest of the atmosphere during their winter and early spring seasons due to a phenomenon known as the "polar vortex". In simplest terms, this vortex is a spinning, funnel shaped region of the atmosphere that forms in late fall and early winter over a pole, allowing chemical reactions in the enclosed air mass to be enhanced due to the lack of mixing with other, lower latitude, air masses. The effect of the pollutants we have added to the atmosphere are thus enhanced in these isolated regions of the atmosphere. The Antarctic vortex over the South Pole is more effective at isolating this region of the atmosphere during the austral winter than is the corresponding arctic vortex. A second feature of the polar stratosphere that is unique and probably aids the polar ozone depletion is polar stratospheric clouds. These very high altitude clouds are composed of ice crystals, sometimes greatly enriched in nitrogen oxide species ("$\ce{NO\_x}$") that can enhance the ozone degradation reactions discussed above. These ice particles can react with various forms of Chlorine in the atmosphere and accumulate the molecule $\ce{ClONO2}$, which is a source of ozone depleting Cl radicals. Once spring time comes, this $\ce{ClONO2}$ decomposes and allows ozone degradation reactions can occur.
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One of the other reason is polar stratospheric clouds (PSCs).



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> The very low winter temperatures in the Antarctic stratosphere cause polar stratospheric clouds (PSCs) to form. Special reactions that occur on PSCs, combined with the relative isolation of polar stratospheric air, allow chlorine and bromine reactions to produce the ozone hole in Antarctic springtime.
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**References**:


1. <https://www.soest.hawaii.edu/GG/ASK/ozonehole.html>
2. <https://csl.noaa.gov/assessments/ozone/2010/twentyquestions/Q10.pdf>
3. <https://uk-air.defra.gov.uk/research/ozone-uv/moreinfo?view=antarctica-hole-explained>
4. <http://cimss.ssec.wisc.edu/wxwise/ozone/OZONE5.html>
5. <https://scied.ucar.edu/learning-zone/atmosphere/ozone-layer>


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