News: Smallest ozone hole in 2017

The ozone hole over Antarctica is very small this year.A recent report by NASA and NOAA shows that this year's ozone hole area has been the smallest since 1988  Fig. 1). According to NASA's data earlier of this month, the Antarctic ozone hole, which is nearly 1 million square miles smaller than that of 2016 (Fig. 2), will continue to shrink. However,    according to Dr Matt Tully, Director of the Bureau of Meteorology for the International Ozone Committee, this does not mean that the hole will soon disappear. Scientists think it is mostly caused by natural reasons rather than the human action. NASA regards the smaller ozone hole this year as a factor in natural change, not "a signal of rapid healing."

Figure 1. Maximum of daily ozone hole area (Source: NASA).

Figure 2. Antarctic Total Ozone of 2016 (left) and 2017 (right) (Source: NASA).

NASA announced that the reason for the smaller ozone hole this year was resulted from the warmer vortex over the Antarctic. The Antarctic vortex is a low-lying, low-pressure region rotating clockwise over the Antarctic. However, since the depletion of ozone occurs in cold environment (for a reference to previous blogs), the ozone hole reaches its annual maximum in September or October at the end of the southern hemisphere winter. This year, however, the system is warmer and more unstable than usual and contributes to reducing clouds in the lower stratosphere which is formed during the Antarctic winter. When the temperature drops below -78 degrees, nitric acid or sulfuric acid particles adsorb water droplets to form larger particles, resulting in large-scale polar stratospheric clouds. These clouds store ozone-depleting substances such as chlorine and bromine (Rowland, 1996). When Antarctic spring comes, the ozone depletion in these clouds will consume a large amount of ozone under UV catalysis. Thus, the warmer stratosphere this year weakened the formation of stratospheric clouds and, as a result, reduced ozone depletion.

Scientists expect that around 2070, the Antarctic ozone hole may recover to 1980 levels .