To sum up！

It is time to summarize, and it is time to answer the question. So "The Ozone Hole: Does it matter or not?". I still think that it does matter.

Looking back at our previous blogs, from the very beginning, we know that the ozone hole has developed and started to shrink. In this November we received news from NASA that the ozone hole had reached the lowest level since 1980. Everything seems to be moving in the right direction, as if humanity's efforts to protect the environment have achieved great success. But when we look at the principles of the formation, development and reduction of the ozone hole, we can no longer maintain a very optimistic attitude. The formation of ozone hole mainly attributes to chemical reasons (Freon, etc.), solar activity causes, the reasons for atmospheric movement and other natural activities (such as volcanic eruptions), a large part of which is beyond human’s control. Humans have limited some of the known major ozone consumption, but new short-lived ozone depleting substances have been discovered without norms and limitations of their use. The reason why the ozone hole is the smallest this year is the abnormal warming in the stratosphere. This means that the seemingly good aspects may only be temporary; while global warming which can be mutually reinforced with the stratospheric ozone hole, is not temporary. In other words, the ozone depletion will recover slowly if global warming cannot be stopped.

Therefore, the whole world should still firmly stand together and contribute to preventing the ozone layer from continuing to grow larger. Although volcanic eruptions or solar activity are beyond control, it is impossible to improve the process of global warming and limit newly-discovered ozone depleting substances.

Pacific Decadal Oscillation (PDO) may affect ozone hole

Pacific Decadal Oscillation (PDO) is a pressure pattern alternating over the Pacific with "warm" and "cold" phases (Newman, et al., 2016), each lasting between 20 and 30 years. For nearly 100 years, it has appeared in two complete cycles. The "cold phase" of two cycles occurred from 1890 to 1924 and from 1947 to 1976;while these of "warm phase" were from 1925 to 1946 and from 1977 to the late1990s.

During the rapid increase of the Antarctic ozone hole from 1978 to 2000, it was in the warm phase of the PDO phenomenon. During the rapid contraction of the Antarctic ozone hole in 1957-1976 and 2002-2004, it was in the cold phase of PDO phenomenon. It can be seen that the Antarctic ozone hole may have relation to the high air pressure flow, which is first and foremost a natural phenomenon.

Volcanic activity affects ozone hole

The mechanism by which volcanic eruption destroys the ozone layer is due to the release of a large amount of ashes (Stenchikov, et al., 2002). After the volcano erupts, ashes will be sent into the stratosphere ( Fig. 1). These ashes contain high concentrations of chlorine and bromine which may stay in the stratosphere for two to five years. During this period, stratospheric ozone is consumed continuously under the influence of solar radiation. It is estimated that volcanic aerosols below 17 km (11.5 mi) above sea level may account for about 18-20% to destroy the ozone layer.

Figure 1. How volcanoes influence ozone layer .

According to the analysis, the formation of the ozone hole over Antarctica in 1992 was caused by the eruption of Pinatubo volcano in the Philippines in 1991 (Fig. 2). Volcanic eruption brought 34-mm-thick plumes into the stratosphere, which had a significant impact on the ozone level. Tabazadeh said: "Both the El Chichon volcano in 1982 and the Pinatubo volcanic eruption in 1991 were sulfur-rich and produced volcanic clouds in the stratosphere for several years." NASA observed that Pinatubo eruptions on the Arctic. The area had widened the ozone layer.

Figure 2. Sulfur Dioxide Cloud over Pinatubo (Source: NASA).

In recent years, many studies show restoration signs of the Antarctic ozone layer. However, in October 2015, the potholes in the ozone layer of the Antarctic were refreshed to the peak of history, triggering doubts about the restoration.Some researchers pointed out that the 2015 figures may result from the Karbubo volcano eruption of Chile in April of that year. Large amounts of volcanic sulfur particles were released into the atmosphere, destroying the ozone layer. Researchers believe that if there is no volcanic eruption, the hole of ozone layer will continue to shrink.

Tabazadeh said: "Volcanic aerosols can cause heavier ozone destruction at warmer temperatures than polar stratospheric clouds do." According to Drdla, volcanic Arctic clouds of 15 to 25 kilometers above sea level (9 to 16 miles)  may increase the spring ozone loss in the Arctic by 70%. Tabazadeh pointed out: "The combination of thicker volcanoes at lower altitudes and natural polar stratospheric clouds at higher elevations could dramatically increase the possibility of Arctic ozone depletion in a cold year.

Climate change combined with large volcanic eruptions will result in ozone loss across the poles, indicating that ozone recovery is more complex than common thought.