Hydrogen has a high energy density and is clean - burning to leave only water vapour.
As the air rises, it expands and cools, and water vapour condenses, releasing even more heat.
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Such particles act as nuclei for the condensation of water vapour into the droplets of which clouds are composed.
They fill the container with pure air made by evaporating liquid nitrogen and liquid oxygen, and add water vapour and some trace gases.
The idea is to test the effects on the atmospheric window of various pollutants, and also of water vapour, by releasing them into the building.
Fuel cells which produce electricity from the combination of hydrogen and oxygen, would supplement other energy sources and release only water vapour into the environment.
Without such particles, clouds would be rare: the air would need to be freakishly saturated with water vapour or strangely cold for condensation to occur.
These are boxes containing air that is super-saturated with water vapour.
One depends on the idea that the water vapour which forms clouds condenses initially around tiny particles known as aerosols (many of which are produced by algae).
Just a fortnight ago, astronomers using the Hubble space telescope identified water vapour in the atmosphere of an exoplanet, albeit a gaseous exoplanet some 150 light years away.
Venus's weather system involves sulphur, carbon monoxide and water vapour.
The consequent condensation of the water vapour it is carrying heats the air further (the change of state from gas to liquid sheds latent heat), causing it to continue rising.
Much of it resulted from volcanoes blasting out gases like carbon dioxide and water vapour, which allowed ice (also a mineral) to form near the poles of Earth, and possibly on Mars too.
These data will provide invaluable information about Antarctic atmospheric dynamics, of the origin of water vapour over the oceans and how it is ultimately deposited as snow on the surface of the ice sheet.
Finally, Declan looked at the BMW Hydrogen 7 - its only emission is water vapour but the technology for this type of green car is still being developed and currently, there are no models on sale.
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Since rising air causes clouds to form (the risen air eventually cools to the temperature of its elevated surroundings, and any water vapour it contains thus condenses), the result would be more rain than would fall in the absence of the artificial aerosols.
He thus put together a collection of apparatus that would not have disgraced the set of a mad-scientist horror film, and filled it with a mixture of methane, ammonia, hydrogen and water vapour that matched contemporary ideas of what the primitive terrestrial atmosphere had been composed of.
Sources of doubt that have seemed plausible in the past, such as a mismatch between temperatures measured by satellites and temperatures measured at the surface, and doubts about the additional warming that can be put down to water vapour, have been in large part resolved, though more work is needed.
When water velocity is high, the pressure within the liquid drops to below the vapour pressure of water, allowing tiny air bubbles to expand.
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