Abstract
The 2024 Southern Hemisphere ozone hole lasted about five months, reached a minimum temperature of 180 K on 8 August, with an area of 22 x 106 km2 on 28 September, with a minimum O3 concentration of 107 Dobson units on 7 October.
The season's ozone hole, on the average, was 26th out of 45 ranked by area, 24th out of 45 ranked by depth, 24th out of 45 ranked by mass deficit, 27th out of 45 ranked by mean ozone concentration, and 24th out of 45 ranked by mean temperature.
By these measures, the past year was an average one over the satellite era.
The world is on track to return the Antarctic stratosphere to pre-1980 levels by approximately 2076, were the general trend of decline to continue.
Data Sources
Normally, I would not start out with this section, but NOAA and NASA are both under attack by the right wing in the current [mis]administration. NOAA monitors ozone-depleting substances worldwide. And NASA satellites monitor ozone. The future existence of the repositories of these data is in doubt. Thus is is not unlikely that, at some point in the not-too-distant future, a click here or there will result in a "404 error".
Introduction
This is a re-analysis of NASA Ozone Watch data for the Southern Hemisphere Ozone Hole. The 2024 antarctic ozone hole closed at the end of December, as is usual. The area (in 106 km2) of the ozone hole is shown in figure 1. As is readily observed, the hole emerged in the late Antarctic winter, mid-July and closed five months later by mid-December. The basic science of stratospheric ozone depletion is well understood.
...the primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction.
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Figure 1. SH Ozone hole area
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The ozone hole is usually characterized by its area, depth, and temperature. These properties are illustrated in the following set of figures.
Figure 2 shows the evolution of the ozone hole area over the years of the satellite era. NASA states "The minimum ozone is found from total ozone satellite measurements south of 40°S. No interpolation of missing values is performed. This means that the actual minimum value on a day may be estimated too high, especially in the polar night region."
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Figure 2. Ozone hole area near September maximum
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Figure three shows the mean amount of Antarctic stratospheric ozone in Dobson Units (DU).
The Dobson unit is defined as the thickness (in units of 10 μm) of that layer of pure gas which would be formed by the total column amount at standard conditions for temperature and pressure (STP). This is sometimes referred to as a 'milli-atmo-centimeter'. A typical column amount of 300 DU of atmospheric ozone therefore would form a 3 mm layer of pure gas at the surface of the Earth if its temperature and pressure conformed to STP.
The annual record is shown and compared with that over the satellite era. Note that the 2024 ozone hole was quite close to the satellite era mean, aside from a short-lived decrease in November 2024.
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Figure 3. The mean ozone, found from
total ozone satellite measurements south of 40°S. |
Figure three shows the mean amount of Antarctic stratospheric ozone in DU. Note the pronounced minimum at the Antarctic spring remains quite pronounced, reaching a low of 109 DU. In this author's opinion, this behavior is not that of an atmosphere healed from the damage of ozone depleting substances.
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Figure 4. The minimum ozone
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Figure 5 shows the temperature of the stratosphere at a pressure of 10 hPa, an altitude of approximately 30 kilometers, averaged around the polar cap for latitudes south of 60°S. NOAA states "This is a good measure of the overall temperature in the polar vortex." Note the temperatures for the formation of type I and type IIU
polar stratospheric clouds (PSC), "composed of mostly supercooled droplets of water and nitric acid and is implicated in the formation of ozone holes." Once again, these data are quite close to the mean over the satellite era.
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Figure 5. The 10 mPa temperature in Kelvin (K)
averaged for 55°S to 75°S. |
The ozone mass deficit is determined from total ozone satellite measurements. It combines the effects of changes in area and depth. It is the total amount of mass that is deficit relative to the amount of mass present for a value of 220 Dobson Units (DU).
This mass deficit reached a peak of 28.20 Megaton ozone in mid-September, slightly higher than the mean over the satellite era.
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| Figure 6. Mass deficit of antarctic stratospheric ozone (Megatons) |
The causes of stratospheric ozone depletion were deduced by Paul J. Crutzen, Mario J. Molina and F. Sherwood Rowland, who were jointly awarded
The Nobel Prize in Chemistry in 1995 "for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone."
When chlorine and bromine atoms come into contact with ozone in the stratosphere, they destroy ozone molecules. One chlorine atom can destroy over 100,000 ozone molecules before it is removed from the stratosphere. Ozone can be destroyed more quickly than it is naturally created.
Some compounds release chlorine or bromine when they are exposed to intense UV light in the stratosphere. These compounds contribute to ozone depletion, and are called ozone-depleting substances (ODS). ODS that release chlorine include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride, and methyl chloroform. ODS that release bromine include halons and methyl bromide. Although ODS are emitted at the Earth’s surface, they are eventually carried into the stratosphere in a process that can take as long as two to five years.
The ODGI is estimated directly from observations at Earth’s surface of the most abundant long-lived, chlorine and bromine containing chemicals whose production and consumption is controlled by the Montreal Protocol (15 individual chemicals). These ongoing, surface-based observations provide a direct measure of nearly all of the chlorine and bromine atoms in the lower atmosphere, or troposphere, contained in chemicals with lifetimes longer than approximately 0.5 yr. Because the lower atmosphere is quite well-mixed, these observations also provide an accurate estimate of the amount of chlorine and bromine entering the stratosphere from these chemicals.
The ODGI is shown in figure eight, "calculated for the Antarctic and mid-latitude stratosphere. As before, the ODGI derived directly from the Equivalent Effective Stratospheric Chlorine (EESC) determined from our atmospheric observations at remote surface sites". The mid-latitude index is seen to have peaked in 1997 and decreased to half its maximum in 2021, clear evidence of the success of the Montreal Protocols.
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| Figure 8. The Ozone Depleting Gas Index (ODGI) vs. time |
Figure nine,
also from NOAA, shows past and projected future changes in reactive halogen concentrations in the atmosphere.
Past concentrations are derived from NOAA measurements of both chlorine- and bromine-containing chemicals; “WMO scenarios” are from the WMO/UNEP 2018 Ozone Assessment, which are tied to NOAA observations in the past and, for the future, assume full adherence to controls on production and consumption of ODSs in the fully revised and amended Montreal Protocol (Carpenter and Daniel et al., 2022). Measured tropospheric changes are indicated with dashed curves and points, while inferred stratospheric changes are indicated as solid curves. Estimates are provided for different regions: the mid-latitude stratosphere and the Antarctic stratosphere. The down-pointing arrows represent the estimated dates that concentrations of stratospheric halogen will return to the benchmark levels present in 1980.
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Figure 9. Past and projected future changes in reactive
halogen concentrations in the atmosphere. |
Of course, the ultimate measure of the success of these policies and treaties is the improvement in human health. Here are some data from the
Ozone Secretariat of the United Nations Environment Programme:
The Montreal Protocol has prevented large increases in surface UV-B radiation, with greatest benefits at high latitudes. Modelling studies indicate that without the Montreal Protocol, at northern and southern latitudes of less than 50° the ultraviolet index (UVI), which indicates the intensity of UV radiation with respect to sunburn, would have increased by 10-20% between 1996 and 2020. This would have increased by 25% at the southern tip of South America and by more than 100% at the South Pole in springtime.
In the United States, full implementation of the Montreal Protocol is expected to prevent approximately 443 million cases of skin cancer, 2.3 million skin cancer deaths, and 63 million cases of cataracts for people born in the years 1890–2100, according to the US Environmental Protection Agency.
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