The Science Behind Ozone Layer Protection and Space

In a region far above the clouds, in a space invisible to anyone looking down below, there’s a thin shield that protects humans from being fried by cosmic rays. That shield — referred to as the ozone layer — protects us from harmful radiation emitted by the sun, without which, Earth would have been inhospitable for plant and animal life alike. But just what is this enigmatic blanket – and how does it connect to the boundless cosmos that lies beyond Earth?

It is a tale of scientific inquiry, environmental disaster and international cooperation. It requires grappling with intricate chemical reactions hundreds of miles above our heads, acknowledging how humanity is affecting whole planetary systems and caring enough to try to save that which allows life to thrive. And as we push outward into space and create new technologies, our interaction with this shield becomes even more important to comprehend.

Here we take a look at the exciting science of the ozone layer, its relationship with space, the challenges it has encountered and how we are working to protect it. We’ll take a look at how this invisible layer functions, why it’s important for exploring both Earth and space and what lies ahead in the future of protecting the ozone layer in a time of climate change and as humans venture further away from our own atmosphere.

What It Is That Makes Ozone So Special

It’s not a hard wall or floor above us. Rather, it’s Earth’s stratosphere, some 15 to 35 kilometers above the surface, where ozone molecules are present in greater quantities than anywhere else in the atmosphere. To appreciate the significance, we must first make sense of what ozone really is and how it’s created.

Ozone is a molecule composed of three atoms of oxygen bound together, and is commonly written in chemical equations as O₃. It isn’t like the oxygen we breathe, which has two oxygen atoms in it (O₂). Ozone, however, is present only in trace amounts across the atmosphere. Although oxygen constitutes approximately 21% of air at Earth’s surface, ozone forms only a fraction of that. The concentration of ozone is greatest in the stratosphere, but even there it accounts for only a few parts per million of the air.

Ozone is naturally produced in the stratosphere by a photochemical reaction powered by solar radiation. When these ultraviolet (UV) rays from the sun reach the upper atmosphere, they bombard oxygen molecules and split them into individual atoms of oxygen. These independent oxygen atoms then collide with other oxygen molecules, and in the right conditions they react together to form ozone. This process of creating and destroying ozone molecules simultaneously living and dying has a delicate stability tens of millions of years in the making.

The Ozone Formation Cycle

This life–death dance is what makes this protective shield so effective. Ozone molecules, the study explains, simply absorb UV radiation and dissociate for a time – the damage is turned into heat. New molecules of ozone are then formed to take the place of those that were destroyed, resulting in a self-renewing protective system.

The Menace of Cosmic Rays: How Space Kills

Space is no empty, peaceable void as it may seem. Our sun irradiates the solar system with radiation of various types, some dangerous to life forms. Knowing about these life-threatening menaces makes us realize how vitally important the ozone layer is to the earth’s inhabitants.

The sun radiates energy over a spectrum of wavelengths that includes everything from radio waves to gamma rays. Much of this radiation is benign or even beneficial — visible light helps us see and infrared light feels warm. But ultraviolet falls into a pernicious class of radiation that can harm biological molecules, especially DNA.

There are three categories of ultraviolet radiation, determined by wavelength: UVA (315-400 nanometers), UVB (280-315 nanometers) and UVC (100-280 nanometers). UVC radiation, which is the most harmful, thankfully never reaches the Earth’s surface since it is entirely absorbed by oxygen and ozone in our atmosphere. The ozone layer absorbs 95 percent of the UVB, but some still reaches the earth. While UVA radiation also penetrates through the atmosphere, it is less harmful than UVB.

Without the ozone shield, there would be full effect of UVB and UVC radiation upon Earth’s surface. The consequences would be catastrophic. High-energy rays can break chemical bonds in DNA molecules, resulting in mutations that are precursors to cancer. They are capable of destroying proteins and other cellular structures, interfering with regular biological processes. Plants would find it nearly impossible to photosynthesize, marine life could vanish as phytoplankton died off, and animals would experience record rates of skin cancer and cataracts.

The relation between the ozone layer and space is even more compelling if we take space exploration into account. For astronauts who leave Earth’s protective atmosphere, exposure to solar and cosmic radiation is unavoidable. The International Space Station orbits some 400 kilometers up, high above the ozone layer and therefore outside of the protective effects that shield crew members. As humans begin to prepare for missions to the Moon and Mars, learning how to replicate the protection that the ozone layer provides will become essential in both spacecraft design and habitat construction.

The Discovery That Changed Everything

Millions of years passed before anyone ever knew the planet was enveloped in an ozone layer, but this story of discovery and understanding turned out to be critical to the evolution of environmental science.

Ozone in the atmosphere was first discovered by scientists in the 1800s, but it wasn’t until the 1920s that researchers started to appreciate its protective function. The basic ideas of the chemistry were laid down finally by an Englishman named Sydney Chapman, who came up with an argument for how ozone might form and decompose in the stratosphere to yield this layer that we still carry with us. For years scientists assumed this natural balance would last forever.

That assumption was shattered in 1974 when the chemists Mario Molina and F. Sherwood Rowland published a seminal paper. They hypothesized that chlorofluorocarbons (CFCs) — artificial chemicals used in refrigerators, air conditioners, aerosol sprays and foam insulation — could ravage ozone molecules in the stratosphere. It was, at the time, a nearly implausible hypothesis. How could emissions released at the earth’s surface impact a layer of atmosphere so distant and lofty?

The reason is the extraordinary stability, not to mention staying power, of CFCs. They are not readily degraded in the lower atmosphere. Instead, they just rise slowly into the stratosphere over a period that can last years. And there, strong UV radiation at last splits apart those CFC molecules to free the chlorine atoms. And then each chlorine atom can destroy many thousands of ozone molecules in a catalytic cycle — meaning it doesn’t use up the chlorine to destroy the ozone, but you can do this over and over again.

Scientists were initially skeptical of the hypothesis by Molina and Rowland, but their predictions have been tragically borne out. It was in 1985 that British scientists conducting research in Antarctica discovered to their horror a huge hole in the ozone layer over the South Pole, during the Antarctic spring. Satellite images provided evidence that the ozone had declined by greater than 50 percent in places, leaving an opening that was even larger than the entire continent of Antarctica.

Life Inside the Ozone Hole

The Antarctic ozone hole has offered scientists a natural laboratory in which to study what takes place when no ozone shielding is available. These unusual conditions over the Antarctic winter and spring are a recipe for ozone destruction.

In the very cold Antarctic winter, stratospheric clouds are created. These polar stratospheric clouds (PSCs) are surfaces on which normal, stable chlorine compounds can be converted into catalytically active forms. These reactive chlorine compounds quickly rip apart ozone when springtime comes and sunlight reaches the region, leading to the “hole” — really a dramatic thinning, not an empty space— in the ozone layer.

Ozone Layer Thickness Comparison

The ozone hole is normally developed in September to October (Antarctic spring) and recovers by December when the temperatures become warmer and atmospheric circulation currents spread the ozone again. But upside down, the hole leaves the Antarctic continent and its surrounding ocean bathed in unprecedented levels of UV radiation.

The ozone hole has been found to cause areas of local high UV on the ground beneath, with observations at research stations in Antarctica showing that not only is this responsible for levels above those typically experienced at lower latitudes, but they exceed what is outside of the hole. Effects on phytoplankton, the tiny organisms that make up the base of ocean food chains, have been documented by marine biologists. Susceptible to UV radiation, these small creatures can also affect an entire ecosystem if the population of phytoplankton is diminished, with ramifications for fish, seals, penguins and whales.

The ozone hole also alters atmospheric circulation patterns, which affect weather and climate around the world, far more than just in Antarctica. Modifications in stratospheric ozone disturb the temperature gradient inducing wind changes. Researchers have connected ozone depletion to shifts in the jet stream of the Southern Hemisphere, alterations in rainfall patterns over Australia and South America and even trends toward warmer temperatures across Antarctica.

Chemical Villains in the Atmosphere

Though CFCs got most of the attention as ozone destroyers, they are not alone. To understand the complexity of the problem and the breadth of the solutions required, one must appreciate this menagerie of ozone-depleting substances.

There are numerous chlorofluorocarbons, which have different chemical structures and potentials of ozone-depletion. CFC-11 and CFC-12 were the most common, present in nearly all refrigerators and cooling units made before the 1990s. They were miracle chemicals when initially created —non-toxic, non-flammable, and extremely stable. And, unfortunately, their stability kept them in the atmosphere for decades or even centuries where they slowly released ozone-killing chlorine atoms.

Halons, also used as fire extinguishants, contain bromine rather than chlorine atoms. Bromine is more efficient than chlorine at destroying ozone and each bromine atom can destroy multiple molecules of ozone. Used in lower quantities than CFCs, halons still made a large contribution to ozone depletion especially when it was used as an agent in the Northern Hemisphere where most fire suppression systems operated.

Other ozone-depleting substances (ODS) have been carbon tetrachloride (used in solvents and in chemical production), methyl chloroform (used for cleaning metal parts and other industrial uses) and methyl bromide (used as a fumigant and pesticide). Each of these substances has a different atmospheric lifetime and ozone impact, making prediction or modeling of an ozone layer recovery difficult.

Common Ozone-Depleting Substances

The realization that a man-made molecule could ruin such a vital system was a wake-up call for civilization. It was a vivid example that what humans do, even for good or relatively safe purposes, has unintended effects throughout the world. This insight would help to birth the modern science of environmentalism, as well as the idea that we are stewards of this planet.

Global Action Saves the Day

The scope of the international response to an escalating ecological crisis, according to overwhelming evidence of its occurrence. The reaction to ozone layer depletion is a classic example of an environmental success story, and one of the most successful instances of global environmental governance.

In 1987, in Montreal, Canada, representatives from two dozen countries came together to sign a treaty that would alter the course of environmental history. Under the Montreal Protocol on Substances that Deplete the Ozone Layer, countries were supposed to eliminate both production and consumption of CFCs and other ozone-depleting substances. Key elements of the pact were timetables, even tougher demands from industrial nations and money for developing countries to switch to alternative technology.

What made the Montreal Protocol so successful was both its flexibility and scientific basis. There were elements of the agreement that allowed for regular review based on new scientific knowledge. Periodically, as knowledge of ozone depletion grew and alternatives to CFCs were developed, the protocol was amended. States also agreed on an accelerated timetable for the elimination of ozone-depleting chemicals, to include new substances and increased funds for transfer of technology.

The protocol also acknowledged that different countries needed to address different challenges. Affluent countries that had used CFCs for decades and could readily afford to move to alternatives had agreed to much faster phase-outs. Developing countries were given more time and financial assistance to make the shift. It accepted historical responsibility but with a mechanism of international participation.

The industries contributed significantly to the success of the protocol. Chemical firms created replacements for CFCs, including hydrofluorocarbons (HFCs) and other substances that don’t deplete the ozone. The refrigerators, the air conditioners and all kinds of other equipment were redesigned to function with these new refrigerants. In some cases companies found ways to reject certain chemicals entirely, using mechanical or other alternative processes.

By 2010, production and consumption of the primary ozone-depleting substances had been reduced by over 98% from peak levels in the late 1980s. The Montreal Protocol was the first international environmental treaty to be universally ratified, with all nations on Earth becoming parties. If not for the protocol, scientists say, the ozone layer would still be diminishing and there would be a possible global hole in the ozone layer by 2050, with disastrous levels of UV rays across much of globe.

Measuring Success from Space

Outer-space satellites are the principal weapons in our arsenal for gauging the health of Earth’s ozone layer. These space-based instruments provide a global view that would not be possible from terrestrial stations alone, retrieving data from all over the planet every day.

NASA’s Aura satellite, which was launched in 2004, has a number of instruments for observing atmospheric chemistry. By recording the UV radiation reflected from Earth’s surface and its atmosphere, the Ozone Monitoring Instrument (OMI) enables measurement of total ozone concentrations with unprecedented accuracy. The Microwave Limb Sounder (MLS) offers profiles of ozone that show how its content changes with altitude.

Sentinel-5P has been the most advanced in a series of atmospheric monitoring satellites developed by ESA, and was launched in 2017. Its instrument TROPOMI is able to measure ozone and other trace gases at an unbeaten spatial resolution, in effect providing us with detailed maps of our atmosphere’s composition that are refreshed daily. This ability facilitates scientific attribution of localized ozone loss, monitoring of the transport of ozone-depleting substances and validation of compliance with international agreements.

It was also complemented by in-situ monitoring stations, which records data from the ground to be stored for many decades. The global network of Dobson spectrophotometers and Brewer spectrometers located around the world measure total column ozone, or the quantity of ozone in a vertical column of the atmosphere, from Earth’s surface to the edge of space. Some of the stations have been running on and off since the 1950s, offering a long-term baseline for studies of changing conditions.

Scientists also measure amounts of ozone at various altitudes as a balloon ascends the atmosphere, using ozonesondes (ozone sondes carried aloft by balloons). These in situ observations serve as a reference to validate satellite retrievals and yield detailed information on ozone distribution within the stratosphere. Specialized instruments are also on board some research aircraft that occasionally fly through the stratosphere, providing complementary data about atmospheric chemistry.

The reams of data from satellites, ground stations and other surveillance instruments leave no room for doubt: The ozone layer is healing. Readings indicate that gases which destroy the ozone layer reached their peak in the late 1990s and it has been going down since then. The Antarctic ozone hole, while continuing to form each spring, has stopped growing bigger and more depleted — a sign of its very slow trajectory back to full health. According to computer models, the layer should recover to its 1980 levels—before scientists discovered an Antarctic ozone hole—around the middle of this century.

For more information about the Montreal Protocol and its success, visit the United Nations Environment Programme’s Ozone Secretariat.

Space Weather and Ozone Interactions

The interaction of space with the ozone layer is not limited to radiation protection. Cosmic rays, solar activity and other space weather events interact with Earth’s atmosphere in complicated ways that impact ozone levels.

The sun has an 11-year cycle of activity that peaks at what is known as solar maximum (high activity), and tapers off to its low point which is solar minimum. At solar maximum, there is more UV radiation from the sun which creates ozone in the stratosphere. But solar activity also creates intense solar flares and coronal mass ejections — giant explosions of plasma from the sun’s surface.

Once those solar flares reach the Earth, they can strike our atmosphere in a number of different ways. Solar storm high-energy particles can boost the production of nitrogen oxides in the upper atmosphere. These nitrogen oxides can then fall into the stratosphere where they destroy ozone by catalytic chemical reaction, just as does chlorine and bromine. Temporary ozone depletions have been observed after large solar storms, but these are mostly short-lived and local phenomena.

Other particles known as cosmic rays, which come from outside the solar system at high energies, also can interact with Earth’s atmosphere. Cosmic rays hitting air molecules result in cascades of secondary particles and ions. A few researchers have also suggested that cosmic ray ionization could have an influence on cloud formation and some aspects of atmospheric chemistry, such as possibly including the amount of ozone, although there are still open questions about these ideas.

The Earth’s magnetic field acts as a shield, keeping out radiation from the sun, cosmic rays and other external sources. But near the magnetic poles, lines come together and bend down toward the surface, allowing more energetic particles to burrow down below. This helps to account for why the ozone hole is most intense over Antarctica, as well as the Arctic experiencing significant ozone loss during winter and spring.

Climate Change and Ozone Recovery

The Montreal Protocol applies to ozone depleting substances, but a new problem has arisen: the relationship between healing the ozone layer and climate change. These two environmental challenges, while separate, overlap in unexpected ways that researchers continue to decode.

Many of the chemicals that were created to substitute CFCs, and especially hydrofluorocarbons (HFCs), do not deplete ozone. But they are powerful greenhouse gases — thousands of times more efficient than carbon dioxide at trapping heat. As the use of HFCs boomed in developing countries that increasingly sought air conditioning and refrigeration, worries rose about their role in global warming.

In 2016, they approved the Kigali Amendment to the Montreal Protocol, which called for a phasedown in production and use of HFCs. The amendment is a relatively unusual demonstration of international climate action taking place within an already established and effective treaty structure. If countries fully implemented the Kigali Amendment, they could avoid as much as 0.5°C of warming by the end of this century without compromising ozone protection, scientists estimate.

And then, of course, climate change itself impacts the ozone layer in a bunch of different ways. Growing greenhouse gas levels warm the lower atmosphere but in fact cool the stratosphere. Colder temperatures in the stratosphere can also increase ozone depletion in the polar regions by leading to the development of polar stratospheric clouds. That sets up a feedback cycle where ozone depletion increases the amount of UV reaching the surface and alters atmospheric chemistry, circulation patterns that may end up changing climate.

Modifications in atmospheric circulation produced by climate change can also influence how ozone is circulated around the globe. The Brewer–Dobson circulation, a giant scale pattern of atmospheric circulation transports air from tropical lower atmosphere to the tropical upper atmosphere and then toward the poles. The intensification or weakening of this meridional circulation could change the amount of ozone in several latitudinal regions, which may affect UV levels at ground level in populated areas.

Preserving the Shield For Generations To Come

While the Montreal Protocol has worked, it is an ongoing challenge and we must always be vigilant and continue conducting research studies to combat this problem through international collaboration.

However, illegal manufacture and use of CFCs continue in several countries. In 2018, scientists recorded unexpected surges in emissions of CFC-11 that indicated unreported production somewhere on the planet. International investigations linked the emissions to eastern China, where some companies that made foam insulation continued using the banned chemical. That episode underscored the importance of having monitoring and enforcement systems in place to catch infringements.

Fresh threats to the ozone develop with advancing technology. Even when rockets aren’t launching, they inject different types of chemicals into the upper atmosphere — water vapor, carbon dioxide and occasionally chlorine compounds. That is why scientists are now studying whether activities like space tourism and launching satellites could have effects on the ozone layer. The present pace of launches does not seem to have serious consequences, but further increase in space activity deserves some attention.

Geoengineering plans—active large-scale interventions with the Earth’s climate system—could have inadvertent effects on the ozone. And some of the proposed methods, like shooting sulfate particles into the stratosphere to reflect sunlight and cool the planet, could change the chemistry of the stratosphere in ways that would interfere with ozone. Scientists warn against any geoengineering strategies, stressing the importance of understanding potential impacts on the ozone layer and other atmospheric processes.

Public education and awareness continue to be of great importance for preventing damage to the ozone layer. Though the Montreal Protocol effectively eliminated most ozone-depleting substances, products with this chemical are still around in older equipment. The correct disposal, and recycling in the case of old refrigerators, air conditioners and fire extinguishers, helps keep these chemicals from entering the atmosphere. Technicians who service refrigeration equipment must learn how to work safely with refrigerants and switch to climate-friendly alternatives.

The View from Space Stations

Working and living on the International Space Station, astronauts witness first-hand the vital need to protect Earth’s atmosphere. From their viewpoint 400 kilometers above the planet, they can see the delicate blue line of air — a thin film resting on just 1 percent of Earth’s radius — against the blackness of space.

Astronauts looking back at Earth from space have described this as the sensation of gaining a new appreciation for their planet’s fragility. That atmosphere, which appears huge from the ground, looks incredibly thin-curtain like-from space. The full habitable zone of our planet — the region with all weather, all life and all the ozone that exists to protect it from space radiation — shows up as a delicate film encircling the globe.

Crew members on the space station conduct scientific experiments to help researchers understand such atmospheric processes as that involved in ozone chemistry. The space station offers a singular environment for testing how materials and biological systems react to higher levels of UV radiation. These analyses are relevant not only to the understanding of ozone protection, but also to technology development for space exploration in future.

As we humans plan to send missions farther from Earth, studying the ozone layer is more relevant than ever. That’s something future Moon bases and Mars habitats will need: Radiation shields to protect inhabitants from the worst of solar and cosmic rays. Knowing more about the chemical and physical processes that make ozone an effective barrier to radiation can inform engineers designing protective systems for spacecraft and extraterrestrial outpost habitats.

Frequently Asked Questions

Can’t we just produce more ozone to replace what was lost?

Scientists can make ozone in a lab but producing a quantity sufficient to refill the stratospheric ozone layer would be impossible — and impractical. The ozone layer is a very large collection of ozone at high altitude all across the planet. Ozone generated at the surface would, in fact, interact with other pollutants to break down long before reaching the stratosphere. The only feasible solution to this problem is to protect the natural ozone-forming process by banning substances that destroy it.

The ozone hole is not the same as global warming, but the two are related.

No, these are different environmental problems — although they also influence each other. The ozone hole is a seasonal thinning of stratospheric ozone, largely caused by human-made chemicals including chlorofluorocarbons. Global warming happens when greenhouse gases, such as carbon dioxide or methane, trap heat in the atmosphere. But some chemicals affect both — CFCs depleted ozone and also acted as greenhouse gases, while some replacements for CFCs protect the ozone layer but exacerbate warming.

Will it ever completely recover?

Mathematical models suggest the world and Southern Hemisphere ozone layers will have returned to 1980 levels (pre-peak depletion), globally by about 2070, with substantial recovery above Antarctica occurring by 2060–2070. Nonetheless, recovery hinges on sustained compliance with the Montreal Protocol and may be influenced as well by climate change, new technologies, and other unknowns. Regular surveillance and scientific study is still necessary.

Is the ozone hole connected to weather and climate?

Yes, stratospheric ozone depletion affects circulation systems in the atmosphere, where temperature and weather occur. The Antarctic ozone hole is associated with altering the Southern Hemisphere jet stream flow, modifying rainfall patterns and temperature trends over Antarctica. There are expectations that some of the effects will decrease as the ozone layer recovers, but it is difficult to predict due to interactions with other agents of climate change.

Are we still vulnerable to UV light?

Recovery of the ozone layer, however, is uneven and regional depletions persist. The level of UV radiation is greatest closer to the equator, at higher elevations and in summer. You need to continue to take sun protection such as sunscreen, protective clothing and avoid overexposure during peak hours.

Do other planets have ozone layers?

Potentially, yes. Such chemical reactions can also lead to an ozone layer on any planet with oxygen in the atmosphere and enough ultraviolet light. Mars has some, but orders of magnitude less than on Earth due to its thin atmosphere and a scarcity of abundant oxygen. Venus has an atmosphere with sulfur compounds that give it a slight UV shield, even though there is no ozone layer. The hunt for ozone on exoplanets would suggest the existence of oxygen and, possibly, life.

Looking Toward Tomorrow

The tale of saving the ozone layer provides hope — and crucial lessons for tackling other global environmental problems. It shows that when presented with unequivocal scientific evidence of a threat, nations can take actions to address it, even if those actions entail large economic and technical transition costs.

It worked because it contained several important elements: good science, flexibility to evolve in the face of better knowledge, recognition of different circumstances among nations and means for monitoring and enforcement. These principles might inform responses to climate change, biodiversity loss and ocean acidification, among other planetary-scale problems confronting humanity.

As we increasingly venture into space and develop more sophisticated technology, our knowledge of Earth’s atmosphere and the role of the ozone layer will grow. Missions to other worlds in the future could uncover atmospheric processes unfamiliar on Earth, adding to our understanding of how planetary atmospheres work and what they can evolve into. This insight could help to protect the breathable atmospheres of Earth and develop life support system for space colonization.

The ozone layer is a reminder that on an extraordinary planet, we get to exist because some of its systems happen to balance out properly. Yet that thin band of ozone molecules meandering through the stratosphere—virtually invisible as it gobbles up life-threatening radiation from space—is just one piece in a complex jigsaw puzzle of interacting forces that ensure our planet is hospitable for us. It’s not only an environmental duty to save these systems; it’s a down payment on humanity’s future, whether that future is based here on Earth or includes settlements among the stars.

The healing of the ozone layer is an encouraging example of what can be done when science, policy and public will converge for a common good. The knowledge gained to preserve the shield of Earth from space radiation is being carried forward in our efforts to meet the environmental challenges of the 21st century; lessons for a sustainable relationship with our home planet and its universe.