Science Questions

Could a straw be used to suck greenhouse gases into space?

Sun, 11th Apr 2010

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Question

James Hamlin asked:

Hi, Chris

 

I have heard the term "vacuum of space" if this is the case, can we use this pressure to rid our atmosphere of unwanted greenhouse gases or smoke?

 

Answer

Dave -   That sounds like a lovely idea.  The problem is, there's nothing actually around the Earth holding the atmosphere in.  There's not like a great big greenhouse holding the atmosphere in.  If you keep on going up, you just hit the vacuum of space anyway.  So what's holding the atmosphere down?  It's just gravity.  The Earth has got enough gravity to hold even the tiny molecule of oxygen down on it.  And the reason why there's so much air pressure pressuring on us now is all of the air above us is getting pulled down by gravity and it's pushing down on us about 10 tons per square meter.  So, if you put a big straw up into space, all you would do is have a straw with air in the bottom and there wouldn't be any air at the top.  I guess you could possibly pump the air out.  But you'd have to push it a long way up for it to get blown away.

Chris -   If you could make a straw 50 miles high, you presumably have got the technology to deal with it another way would be my argument, wouldn't it?

Dave -   And it would probably take more energy than not burning the fuel in first place.

Chris -   But an impressive sight, though, wouldn't it?

Dave -   It would.

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James Hamlin asked the Naked Scientists: Hi, Chris I have heard the term "vacuum of space" if this is the case, can we use this pressure to rid our atmosphere of unwanted greenhouse gases or smoke? Like a straw in a balloon. We may need to wait for carbon nano-tubes. And with that, could we also use these "tubes" as pnuematic space elevators? Such as at the bank drive up teller.  What do you think? James Hamlin , Fri, 9th Apr 2010

Hi James. Unfortunately such a system can't work. What you think of as "sucking" is really the higher pressure side "pushing". A vacuum is the absence of anything pushing back! The earth's atmosphere has pressure as the result of gravity acting on all the air molecules. The gravity also keeps the atmoshere on the earth. As you go higher the pressure gradually gets lower until there is a negligible amount of atmosphere. Having a pipe extending into space would behave exactly as the air outside the pipe. The pressure inside the pipe would be the same as outside and reduce in the same way as you went higher. In the same way as the air outside the weight of air inside the pipe would produce the same pressure gradient.

I hope this explains it. graham.d, Fri, 9th Apr 2010

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