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Absorption and emission of EM radiation: 5. The super 'greenhouse effect' of the mainly carbon dioxide atmosphere of the planet Venus

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EMR shorthand for electromagnetic radiation

INDEX of physics notes: Absorption & emission of EM Eradiation by materials - temperature and surface factors


5. The super 'greenhouse effect' of the mainly carbon dioxide atmosphere of planet Venus


Venus is the 2nd planet from the Sun and is named after the Roman goddess of love and beauty - perhaps because it shone the brightest of the five planets known to ancient astronomers - but looks can be deceptive, Venus has no love for the human body!

The surface temperature of Venus is up to 465oC.

The surface atmospheric pressure is 90 atm (90 x that on Earth).

The lower atmosphere is mainly carbon dioxide (96.5% CO2) and nitrogen (3.5% N2).

[in the lower atmosphere and upper clouds there may be small amounts of sulfur dioxide (SO2), oxygen (O2), water (H2O), noble gases - helium (He), neon (Ne) & argon (Ar), carbon monoxide (CO), sulfuric acid (H2SO4), basalt rock particles and iron(III) chloride (FeCl3)]

The surface area and volume are about 0.9 x that of Earth.

On Venus it rains sulfuric acid, but this evaporates before reaching the very hot surface

The surface of Venus is dry because it is too hot for liquids to condense on

The surface of Venus is relatively flat but very volcanic with still some active volcanoes.

The dense lower carbon dioxide atmosphere is encased in 80 km thick clouds of mainly sulfuric acid (H2SO4) and some sulfur dioxide (SO2) - these clouds reflect 90% of sunlight - which is why it seems so bright, as well as being closer to the Sun than the Earth.

This reflection of sunlight would tend to make the planet cooler - a global dimming effect.

BUT, the hot surface of over 460oC is a powerful emitter of infrared EM radiation.

This thermal radiation is absorbed by the lower carbon dioxide rich atmosphere (96.5% CO2).

This produces a super greenhouse effect compared to planet Earth (0.04% atmospheric carbon dioxide).

Little (if any?) infrared radiation escapes from the planet's atmosphere.

So the surface temperature is kept at a much higher temperature than if the infrared could escape and the net effect completely overrides the dimming effect of the outer reflective clouds.

Note:

(a) Compared to Earth the surface temperature is much hotter - a much stronger emitter of infrared EM radiation AND the atmospheric carbon dioxide concentration is 2400 x that of Earth! - 2400 x the greenhouse effect of carbon dioxide gas on Earth!

(b) The greenhouse effect on Venus is different to that on Earth in one respect - it doesn't actually involve the absorption and remission of infrared radiation - the infrared source on Venus is only from the hot surface.

 

INDEX physics notes: Absorption and emission of EM radiation by materials


Keywords, phrases and learning objectives for absorption and emission of radiation

Be able to describe and explain the super 'greenhouse effect' of the high concentration of carbon dioxide atmosphere of planet Venus which produce a much higher surface temperature.


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INDEX physics notes: Absorption and emission of EM radiation by materials

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