60 Fun Facts About Atmosphere

By volume, roughly 78% of dry air is which gas?

It became the dominant component of Earth's 'second atmosphere' about 3.4 billion years ago, long before oxygen showed up.

About what percentage of dry air is oxygen?

That share is not fixed forever: it has swung over the past 600 million years and once peaked around 35%, high enough to feed giant dragonflies.

After the two dominant gases, what is the third most abundant gas in dry air?

At 0.93% it outweighs CO2 more than twenty to one. Neon, helium and krypton are also present in trace amounts.

CO2 makes up roughly what fraction of dry air by volume?

Small as it is, that trace of CO2 with water vapor keeps the surface roughly 33 °C warmer than it would otherwise be.

At what altitude is the Kármán line, the conventional edge of space?

Theodore von Kármán actually calculated an aeroplane flight limit of 83.8 km; the round-number line above it was fixed in the 1960s and has no distinct physical significance.

Which record-keeping body's Kármán line definition separates aeronautics from astronautics?

The Fédération Aéronautique Internationale counts anything below the line as an air sport and anything above it as astronautics; international law still has no legal definition of where space begins.

Which is the lowest layer of the atmosphere, where nearly all weather happens?

It holds roughly 80% of the atmosphere's mass and nearly all its water vapor, and it is the only layer propeller aircraft can reach.

The ozone layer sits within which layer of the atmosphere?

Because ozone absorbs solar UV there, this is the one layer where temperature rises with altitude, which makes it very stable and almost cloud-free.

Which layer of the atmosphere is the coldest place on Earth and where most meteors burn up?

Its top averages around −85 °C. It is too high for jets and balloons and too low for orbiting spacecraft, so it is mostly studied with sounding rockets.

The International Space Station orbits within which layer of the atmosphere?

Enough air remains at 400 km that the station needs regular reboosts to counter drag, otherwise its orbit would decay.

What is the outermost layer of Earth's atmosphere called?

It is so tenuous that particles travel hundreds of kilometres without colliding, and some scientists count it as interplanetary space rather than atmosphere.

The name of the lowest atmospheric layer comes from the Greek word tropos, meaning what?

The name refers to the constant vertical mixing driven by warm surface air rising and cooler air sinking.

Temperature rises with height in the ozone layer because ozone absorbs what?

That inversion suppresses turbulence, which is why airliners cruising at the bottom of this region get such a smooth ride.

What phenomenon, in which shorter wavelengths scatter more than longer ones, makes the sky look blue?

The same effect reddens sunsets: with a longer path through the air, most of the blue has been scattered away before the light reaches you.

Without greenhouse gases, what would Earth's average surface temperature be?

The actual average is about 15 °C. Water vapor and CO2 absorb and re-emit infrared while letting visible sunlight through.

Which two French physicists discovered the ozone layer in 1913?

They noticed sunlight reaching the ground was missing everything below about 310 nm and matched the absent spectrum to a single known chemical.

The Dobson unit, used to measure ozone overhead, honors G. M. B. Dobson, who was what?

He built a simple spectrophotometer and, between 1928 and 1958, set up a worldwide network of ozone monitoring stations that still operates.

Roughly what share of the Sun's medium-frequency UV light does the ozone layer absorb?

That band, roughly 200 to 315 nm, is the part that damages DNA; the layer itself only holds 8 to 15 parts per million of ozone.

In what year was the Montreal Protocol on ozone-depleting substances agreed?

It entered into force on 1 January 1989 and has been amended eight times since, most recently in Kigali (2016) and Quito (2018).

What distinction does the Montreal Protocol hold among treaties?

All 197 states plus the European Union have ratified it, and Kofi Annan called it perhaps the single most successful international agreement to date.

The UN's International Day for the Preservation of the Ozone Layer falls on which date?

It marks the day the Montreal Protocol was agreed. April 22 is Earth Day and June 5 is World Environment Day.

Springtime ozone losses of up to 70% over Antarctica were first reported in which year?

Joseph Farman and colleagues published the finding; reactions on polar stratospheric clouds explain why the hole is deepest over Antarctica.

What did Paul Crutzen, Mario Molina and Sherwood Rowland jointly receive in 1995 for their work on ozone?

Rowland and Molina's 1974 CFC hypothesis was denounced by DuPont's chairman as 'a science fiction tale ... utter nonsense'.

Which manufactured chemicals were the main cause of ozone depletion?

CFCs were used as refrigerants, solvents, propellants and foam-blowing agents; halons and HCFCs are also on the banned list.

The common green colour of an aurora is emitted by which excited species?

Red auroras come from the same atoms higher up, at 630 nm, and need stronger solar activity to be visible; blue and purple come from other molecules lower down.

The word 'aurora' comes from the Roman goddess of what?

She travelled from east to west announcing the coming of the Sun. 'Borealis' and 'australis' come from the gods of the north and south winds.

Which scientist used the term 'aurora borealis' in his writings about the lights in 1619?

Pierre Gassendi, who had read Galileo, popularized it in a 1649 description of a display seen all over France; the term entered English in 1828.

Noctilucent clouds, the highest clouds in the atmosphere, are made of what?

They form near 76 to 85 km and can only be seen in twilight, when the ground is dark but the clouds are still lit by the Sun.

Noctilucent clouds were first recorded in 1885, two years after the eruption of which volcano?

Whether the eruption created them or simply had more people staring at spectacular sunsets is still unclear.

What does 'noctilucent' roughly mean in Latin?

They are too faint to see in daylight and are mostly spotted in summer between latitudes 50° and 70°.

Who is usually credited with inventing the barometer in 1643?

He was Galileo's assistant in the last months of Galileo's life and argued that the weight of the air, not a vacuum's pull, held the mercury up.

What is standard sea-level atmospheric pressure in hectopascals?

That equals 760 mmHg or 14.7 psi. Weather reports in the US still use inches of mercury (29.92 inHg).

The lowest non-tornadic air pressure ever measured, 870 hPa, was recorded in 1979 inside which storm?

A reconnaissance aircraft took the reading in the western Pacific; Tip was also the largest tropical cyclone on record by diameter.

The record 1,084.8 hPa sea-level-adjusted pressure was measured in 2001 in which country?

The reading came from Tosontsengel during the Siberian High, which routinely pushes winter pressures above 1,050 hPa.

Roughly what share of the atmosphere's mass lies below 16 km (52,000 ft)?

Half of it is below 5.6 km, so a climber on Everest's summit is already above about a third of the air.

The Great Oxidation Event about 2.4 billion years ago is credited to oxygen produced by which organisms?

Free oxygen was toxic to most life at the time, which is why the event is also called the Oxygen Catastrophe.

Atmospheric oxygen peaked at about 35% around 280 million years ago, during which geological period?

That oxygen-rich air is one explanation for the era's giant insects, including dragonflies with wingspans over 60 cm.

What is the speed of sound in air at sea level?

It depends on temperature, not pressure, so it drops to about 290 m/s in the −60 °C air where airliners cruise.

In which direction do the jet streams flow?

They form where the Hadley, Ferrel and Polar cells meet, around 9,100 m up, and are strongest in winter; that is why flights from the US to Europe are faster than the return.

In which language did Wasaburo Oishi publish his 1920s jet stream discovery, leaving it largely unnoticed?

He tracked pilot balloons near Mount Fuji. Real understanding of jet streams is often credited to WWII bomber crews hitting 100 mph tailwinds.

Venus's atmosphere is 96.5% which gas?

The remaining 3.5% is almost all one other gas, under decks of sulfuric-acid cloud that hid the surface from telescopes until radar mapping.

Surface pressure on Venus, about 93 bar, equals the pressure at roughly what depth under water on Earth?

Combined with a surface temperature of 467 °C, that is why Soviet Venera landers survived only minutes to a couple of hours.

Venus spins very slowly (a sidereal rotation is 243 times longer than Earth's), yet its upper atmosphere laps the planet in roughly what time?

This 'super-rotation' means winds blow at up to 60 times the planet's spin; on Earth the fastest winds are only 10 to 20% of rotation speed.

The average surface pressure on Mars is roughly what fraction of Earth's?

At about 610 pascals it is too thin for liquid water to persist on the surface, and a quarter of it freezes onto the polar caps each winter.

Which moon is the only natural satellite in the Solar System with an atmosphere denser than Earth's?

Its surface pressure is about 1.5 bar. Triton is the only other moon with enough atmosphere to drive weather.

Titan's surface pressure allows which substance to exist as a liquid on its surface?

Its orange haze is thought to come from tholins, tar-like organic compounds formed from the same gas.

Edward Appleton won the 1947 Nobel Prize in Physics for confirming which region of the atmosphere?

His 1927 radio-sounding work explained how shortwave signals bounce around the curve of the Earth, as Marconi's 1901 transatlantic transmission had shown they could.

How much hydrogen does Earth lose to space every second?

Helium leaks at about 50 grams a second. The particles escape from the outermost layer along ballistic paths without ever colliding.

How early Earth stayed warm enough for liquid water when the Sun was 30% dimmer is a puzzle known as what?

Much higher levels of greenhouse gases in the early atmosphere are the leading explanation.

Which noble gas is unexpectedly scarce in the atmosphere, a mystery known as 'the missing X problem'?

Proposed hiding places include iron oxides in the lower mantle and reactions with iron and nickel in the core.

Near sea level, air pressure drops by roughly how much for every 100 metres of altitude?

The decrease is exponential: pressure falls by a factor of e roughly every 5.5 to 6 km, so it halves about every 5.5 km.

How hot can the thin gas of the atmosphere's second-highest layer get?

Molecules there travel about a kilometre between collisions, far too sparse to conduct meaningful heat to skin or spacecraft.

Mirages occur because the refractive index of air changes with which property?

Steep temperature gradients bend light rays; the same effect can let ships' observers see objects beyond the horizon.

Earth's first atmosphere, in the Hadean eon, was made primarily of which gas?

Simple hydrides such as water vapour, methane and ammonia probably accompanied it, as on the gas giants today.

The troposphere is about 9 km deep at the poles; roughly how deep is it at the Equator?

Its average height is around 12 km, and 90% of the atmosphere's water vapour sits in its lowest part.

What name is given to the well-mixed lower atmosphere, up to about 100 km, where gas ratios stay constant?

Above it, in the heterosphere, composition changes with altitude because particles rarely collide.

About 3.4 billion years ago, which gas had become the main component of Earth's stable 'second atmosphere'?

Free oxygen would not accumulate until the Great Oxidation Event around 2.4 billion years ago.

What is the approximate density of air at sea level?

Density is not measured directly but calculated from temperature, pressure and humidity using the ideal gas law.

At roughly what altitude does ozone reach its peak concentration of 15 parts per million?

Even at its peak, ozone is a tiny fraction of the air compared with the main constituents.

What is the region of the atmosphere in which the barometric law applies, from the ground to the thermopause, called?

Above it, fast atoms and molecules can escape into space, so the velocity distribution is no longer Maxwellian.