The Ozone Layer
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50 free The Ozone Layer trivia questions with answers — science & nature quiz, new questions added Oct 2026.
The ozone layer is one of the few environmental stories with a hopeful ending. A thin band of gas high in the upper atmosphere screens out most of the Sun's harmful ultraviolet light, and in the 1970s and 1980s scientists found that everyday chemicals were eating it away. What followed was a scientific detective story and an international agreement that actually worked. This quiz covers the whole arc. There are questions on what ozone is and where it sits, how it forms and what it blocks, and why the same gas is a shield overhead and a pollutant at street level. Others follow the science of ozone depletion: the chemicals involved, the discovery of the ozone hole, the researchers who raised the alarm, and the treaty that phased the culprits out. A few look at the numbers that matter and the odd corners of the story, from early inventors to other planets. It suits students revising atmospheric science or environmental studies, teachers who want a ready-made classroom round, and anyone curious about how a global problem was identified and turned around. Every answer comes with a short explanation.
30 of 50 questions with answers and explanations. Play the quiz
Q 01If all of Earth's ozone layer were compressed to sea-level air pressure, roughly how thick a band would it form?
3 millimetres
3 millimetres is all it would make, about an eighth of an inch, because ozone is never more than about 15 parts per million of the air around it.
Q 02Over which continent does a hole in the ozone layer open each year, as British scientists first reported in 1985?
Antarctica
Antarctica gets the hole because its winter air turns cold enough for ice clouds to form, and reactions on those clouds prime CFC leftovers to attack ozone once the Sun returns.
Q 03Thomas Midgley, who helped develop the first CFCs, had earlier put which toxic metal into gasoline to stop engine knock?
Lead
Lead went into petrol in the 1920s thanks to Midgley, and both it and his CFCs were later banned from common use for the harm they did to health and the environment.
Q 04The name ozone comes from a Greek verb describing which of the senses, because of how the gas was first noticed?
Smell
Smell is the root: chemist Christian Schönbein took the name from the Greek ozein after noticing the same sharp odour that hangs in the air following a lightning strike.
Q 05Which layer of the atmosphere, sitting directly above the one where weather happens, holds about 90% of Earth's ozone?
Stratosphere
Stratosphere temperatures rise with height because the ozone there soaks up ultraviolet energy, and long-haul airliners cruise in the layer's lower reaches.
Q 06Which city gave its name to the 1987 treaty that phased out CFCs, later revised in London, Copenhagen and Beijing?
Montreal
Montreal hosted the signing on 16 September 1987, a date the United Nations now marks each year as the International Day for the Preservation of the Ozone Layer.
Q 07Under which DuPont trademark, which became a generic word for refrigerant gases, were the first CFCs sold?
Freon
Freon was launched in 1930 by a joint venture of General Motors and DuPont as a safe replacement for dangerous refrigerants such as ammonia.
Q 08The ultraviolet light that gets past the ozone layer lets the human body make which nutrient, vital for healthy bones?
Vitamin D
Vitamin D is made in the body under the longest wavelengths of the Sun's burning rays, the fraction that ozone does not fully screen out.
Q 09Which household products did the US, Canada and Norway bar from using CFCs in 1978, before any ozone hole was known?
Aerosol sprays
Aerosol sprays were already losing favour: American sales had fallen by half before the law took effect, while CFCs stayed legal in fridges and for cleaning circuit boards.
Q 10The US EPA credits the ozone layer treaty with preventing hundreds of millions of American cases of which disease?
Skin cancer
Skin cancer is the main human cost of extra ultraviolet light, and the same estimate counts more than a million American deaths from it avoided.
Q 11Which element, freed when ultraviolet light breaks up CFCs, destroys ozone in a chain reaction without being used up?
Chlorine
Chlorine acts as a catalyst: each atom is set free again after every ozone molecule it breaks, ready to attack the next one.
Q 12Which chemical formula belongs to ozone, the gas that shields life on Earth from the Sun's ultraviolet rays?
O3
O3 means three oxygen atoms in one molecule, an arrangement so unstable that ozone near the ground soon falls back into ordinary O2.
Q 13Near the ground, ozone formed from traffic fumes and sunlight is a key ingredient of which summer air pollution?
Smog
Smog-forming ozone is the same molecule that shields the planet higher up, but breathed in at street level it reduces lung function and makes deep breaths harder.
Q 21Besides Earth, which planet did a European orbiter find in 2011 to have its own thin ozone layer?
Venus
Venus keeps its thin ozone layer about 100 kilometres above the surface, roughly four times higher than Earth's, where the Venus Express probe detected it.
Q 22Which band of ultraviolet light, the main cause of sunburn, is mostly but not wholly absorbed by the ozone layer?
UV-B
UV-B is filtered so well that at one wavelength it is 350 million times weaker at ground level than at the top of the atmosphere, yet enough still gets through to burn.
Q 23Which scientist's name is on the unit for the total ozone overhead, a scale on which 300 is a typical reading?
Dobson
Dobson units honour Gordon Dobson, who in the 1920s built the first instrument able to measure total ozone from the ground, the same design that later revealed the ozone hole.
Q 14More ultraviolet light under thin ozone raises the risk of which eye condition, the world's top cause of blindness?
Cataracts
Cataracts cloud the lens of the eye, and studies link the kind that forms in the lens's outer layer to long exposure to the Sun's burning rays.
Q 15In which season of the southern hemisphere's year does the ozone hole open each year?
Spring
Spring sunlight supplies the energy for the ozone-destroying reactions, so the hole is deepest in September and October rather than in the depths of the polar night.
Q 16Halons, ozone-depleting bromine compounds, protected aircraft and computer rooms as the agent in which safety equipment?
Fire extinguishers
Fire extinguishers filled with halon stop a flame's chain reaction at low concentrations, but their bromine destroys ozone even more efficiently, atom for atom, than what CFCs release.
Q 17Which daily forecast scale, running from 0 to 11+, did Canadian scientists create in 1992 amid worry about ozone loss?
UV index
UV index readings were adopted worldwide by the World Health Organization in 1994, and values beyond the original top of the scale now occur where ozone has thinned.
Q 18Roughly how high above the ground is the middle of the ozone layer, well above the cruising height of airliners?
25 km
25 km up is the middle of a band running from about 15 to 35 kilometres, more than twice the height at which passenger jets cruise.
Q 19Which British prime minister, once a research chemist, was instrumental in ratifying the treaty that phased out CFCs?
Margaret Thatcher
Margaret Thatcher studied chemistry at Oxford before entering politics, and in office she also helped found the Hadley Centre for climate research.
Q 20Even tiny traces of ozone in the air cause cracking in which material, used for fuel lines, seals and gaskets?
Rubber
Rubber cracks because ozone attacks the double bonds in its molecular chains, a fault that was once very common in tyres until makers took preventive measures.
Q 24The ring of winter winds that seals off polar air, letting the ozone hole form, is known as the polar what?
Vortex
Vortex winds trap and chill the air inside them, and the ozone hole lasts until the ring breaks apart around mid-December.
Q 25A single atom of the ozone-destroying element in CFCs can break down roughly how many ozone molecules on average?
About 100,000
About 100,000 is the average tally, because each atom works as a catalyst and is released to strike again until some other reaction finally locks it away.
Q 26Most of Earth's ozone is produced over which region before high-altitude winds spread it around the globe?
The tropics
The tropics get the strongest sunlight for splitting oxygen, yet the ozone layer ends up thinner there than near the poles because circulation keeps exporting what is made.
Q 27Which chemicals replaced CFCs in fridges without harming ozone, only to be curbed in 2016 as potent greenhouse gases?
HFCs
HFCs leave the ozone layer alone but can trap thousands of times more heat than carbon dioxide, so countries pledged to cut their use by more than 80% over 30 years.
Q 28The 1987 treaty protecting the ozone layer became the first in United Nations history to achieve which milestone?
Universal ratification
Universal ratification means 198 parties, 197 states plus the European Union, have bound themselves to the treaty, something no earlier UN agreement had managed.
Q 29In March 2020, record cold in the upper atmosphere opened a rare ozone hole over which region, far from the usual one?
The Arctic
The Arctic is rarely cold enough for this, but that March instruments carried aloft there measured a drop of about 90% in ozone at the height where it normally peaks.
Q 30Rogue emissions of the banned gas CFC-11, rising since 2013, were traced by researchers mainly to which country?
China
China's north-east was identified as the main origin, and scientists warned that, left unchecked, the leak could delay the ozone hole's recovery by a decade.