50 Fun Facts About The Ozone Layer

If all of Earth's ozone layer were compressed to sea-level air pressure, roughly how thick a band would it form?

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.

Over which continent does a hole in the ozone layer open each year, as British scientists first reported in 1985?

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.

Thomas Midgley, who helped develop the first CFCs, had earlier put which toxic metal into gasoline to stop engine knock?

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.

The name ozone comes from a Greek verb describing which of the senses, because of how the gas was first noticed?

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.

Which layer of the atmosphere, sitting directly above the one where weather happens, holds about 90% of Earth's ozone?

Stratosphere temperatures rise with height because the ozone there soaks up ultraviolet energy, and long-haul airliners cruise in the layer's lower reaches.

Which city gave its name to the 1987 treaty that phased out CFCs, later revised in London, Copenhagen and Beijing?

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.

Under which DuPont trademark, which became a generic word for refrigerant gases, were the first CFCs sold?

Freon was launched in 1930 by a joint venture of General Motors and DuPont as a safe replacement for dangerous refrigerants such as ammonia.

The ultraviolet light that gets past the ozone layer lets the human body make which nutrient, vital for healthy bones?

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.

Which household products did the US, Canada and Norway bar from using CFCs in 1978, before any ozone hole was known?

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.

The US EPA credits the ozone layer treaty with preventing hundreds of millions of American cases of which disease?

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.

Which element, freed when ultraviolet light breaks up CFCs, destroys ozone in a chain reaction without being used up?

Chlorine acts as a catalyst: each atom is set free again after every ozone molecule it breaks, ready to attack the next one.

Which chemical formula belongs to ozone, the gas that shields life on Earth from the Sun's ultraviolet rays?

O3 means three oxygen atoms in one molecule, an arrangement so unstable that ozone near the ground soon falls back into ordinary O2.

Near the ground, ozone formed from traffic fumes and sunlight is a key ingredient of which summer air pollution?

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.

More ultraviolet light under thin ozone raises the risk of which eye condition, the world's top cause of blindness?

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.

In which season of the southern hemisphere's year does the ozone hole open each year?

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.

Halons, ozone-depleting bromine compounds, protected aircraft and computer rooms as the agent in which safety equipment?

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.

Which daily forecast scale, running from 0 to 11+, did Canadian scientists create in 1992 amid worry about ozone loss?

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.

Roughly how high above the ground is the middle of the ozone layer, well above the cruising height of airliners?

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.

Which British prime minister, once a research chemist, was instrumental in ratifying the treaty that phased out CFCs?

Margaret Thatcher studied chemistry at Oxford before entering politics, and in office she also helped found the Hadley Centre for climate research.

Even tiny traces of ozone in the air cause cracking in which material, used for fuel lines, seals and gaskets?

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.

Besides Earth, which planet did a European orbiter find in 2011 to have its own thin ozone layer?

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.

Which band of ultraviolet light, the main cause of sunburn, is mostly but not wholly absorbed by the ozone layer?

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.

Which scientist's name is on the unit for the total ozone overhead, a scale on which 300 is a typical reading?

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.

The ring of winter winds that seals off polar air, letting the ozone hole form, is known as the polar what?

Vortex winds trap and chill the air inside them, and the ozone hole lasts until the ring breaks apart around mid-December.

A single atom of the ozone-destroying element in CFCs can break down roughly how many ozone molecules on average?

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.

Most of Earth's ozone is produced over which region before high-altitude winds spread it around the globe?

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.

Which chemicals replaced CFCs in fridges without harming ozone, only to be curbed in 2016 as potent greenhouse gases?

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.

The 1987 treaty protecting the ozone layer became the first in United Nations history to achieve which milestone?

Universal ratification means 198 parties, 197 states plus the European Union, have bound themselves to the treaty, something no earlier UN agreement had managed.

In March 2020, record cold in the upper atmosphere opened a rare ozone hole over which region, far from the usual one?

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.

Rogue emissions of the banned gas CFC-11, rising since 2013, were traced by researchers mainly to which country?

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.

Which campaign group took up an ozone-safe fridge in 1992 that is cooled by a mix of propane and butane?

Greenpeace named the German design Greenfreeze, and from 2004 companies including Coca-Cola, Carlsberg and IKEA joined a coalition to promote it.

Which medical devices kept an essential-use exemption to go on using CFCs after other uses were phased out?

Asthma inhalers relied on CFCs to push each dose out of the canister, and makers were given extra years to switch to an ozone-safe propellant.

Which gas, released largely from fertilised farm soils, had become the biggest ozone-depleting human emission by 2009?

Nitrous oxide, the laughing gas of the dentist's chair, is made by soil microbes digesting nitrogen fertiliser, and unlike CFCs it is not covered by the ozone treaty.

Which Philippine volcano's huge 1991 eruption cooled the planet by half a degree and temporarily worsened ozone loss?

Pinatubo produced the second-largest eruption of the 1900s and released about 20 million tonnes of sulfur dioxide.

Pure ozone gas, unlike the colourless oxygen it forms from, has which faint tint that deepens when it is liquefied?

Pale blue ozone gas condenses to a dark blue liquid and then a violet-black solid, and in concentrated form it can decompose explosively.

Christian Schönbein, who identified ozone, also discovered which explosive, reportedly after a spill in his kitchen?

Guncotton is said to have revealed itself when Schönbein mopped up spilled acids with a cotton apron, hung it by the stove to dry and watched it vanish in a flash.

Charles Fabry and Henri Buisson, who discovered the ozone layer in 1913, were physicists from which country?

France's Fabry and Buisson noticed that sunlight reaching the ground was missing its shortest ultraviolet wavelengths and traced the gap to ozone high overhead.

Which British scientist, famous for the Gaia hypothesis, built the detector that first tracked CFCs in the air?

James Lovelock invented the electron capture detector, and on a voyage to the Antarctic he found CFCs in all 50 air samples he took, yet judged them no conceivable hazard.

Paul Crutzen, a Nobel laureate for his ozone research, later popularised which name for a proposed geological epoch?

Anthropocene describes an age in which human activity reshapes the planet, a term Crutzen spread after sharing the 1995 chemistry prize with two fellow ozone researchers.

Mario Molina, who shared a Nobel Prize for showing that CFCs threaten the ozone layer, was born in which country?

Mexico City was his birthplace, and Molina became the first Mexican-born scientist to win the Nobel Prize in Chemistry.

Roughly how long can a CFC molecule survive in the atmosphere, which is why the ozone layer heals so slowly?

About a century is the upper range, with lifetimes running from 50 to more than 100 years, so gases released in the 1970s are still at work overhead.

Which African capital gave its name to the 2016 amendment that extended the ozone treaty to climate-warming coolants?

Kigali hosted the treaty's 28th meeting of the parties, where seven years of negotiation ended in a deal that came into force at the start of 2019.

Which European city hosted the 1985 convention that set the framework for the later treaty banning CFCs?

Vienna's convention contained no legally binding targets for cutting CFCs, but it supplied the framework on which the binding treaty was built two years later.

Methyl bromide, an ozone-depleting gas, was widely used by strawberry and almond growers to do what before planting?

Growers used the gas to sterilise the soil before planting, and it was added to the ozone treaty's list of controlled substances at a 1992 meeting.

Which NASA satellite series, whose seventh craft launched in 1978, carried the TOMS instrument that mapped ozone daily?

Nimbus 7 and the later Meteor-3 craft together gave a complete daily record of global ozone from November 1978 to December 1994.

Which American chemist led the 1986 National Ozone Expedition that confirmed how CFCs carve out the ozone hole?

Susan Solomon headed the expedition alone and was the only woman on the team, and she had already proposed that reactions on icy cloud particles drive the losses.

Joe Farman's team revealed the ozone hole in which journal, which had also carried the first CFC warning in 1974?

Nature ran the paper in May 1985, and it shocked researchers because the drop in polar ozone was far larger than anyone had anticipated.

Before CFCs were blamed, scientists in the early 1970s feared ozone damage from the exhaust of which planned aircraft?

Supersonic transports would have cruised inside the ozone layer itself, and Paul Crutzen and Harold Johnston warned that a fleet of a few hundred Boeing 2707s could erode it.

Which British scientist worked out in 1930 how sunlight both makes and destroys ozone, in a cycle now named after him?

Sydney Chapman, a mathematician and geophysicist, showed that ultraviolet light splits oxygen molecules into atoms, which then join intact molecules to form ozone.

Which UN Secretary-General called the 1987 ozone treaty perhaps the most successful international agreement to date?

Kofi Annan's praise has held up: by 2003 the rate of ozone loss had slowed markedly, and a gradual trend toward healing was reported in 2016.