Naked Science Forum

Life Sciences => The Environment => Topic started by: melaniejs on 16/03/2020 17:30:28

Title: As methane is less dense than air, does it float out of atmosphere?
Post by: melaniejs on 16/03/2020 17:30:28
Philip asks:

Accepting that Methane is a "worse" Greenhouse Gas than CO2, as its density is about 0.6 that of Air, won't it "float"? to the upper atmosphere& ultimately Space(?) avoiding a problem?

Anyone know?
Title: Re: As methane is less dense than air, does it float out of atmosphere?
Post by: Kryptid on 16/03/2020 20:03:34
Ultimately, virtually all gas in our atmosphere will eventually be lost to space. There is a distribution of particle velocities in a gas, with most of them falling around some mean value. There is also a percentage of outlier molecules that move much more quickly than the mean value. Some of those molecules will be moving faster than the Earth's escape velocity. Those molecules will, of course, be capable of escaping the Earth's gravitational pull. This is one fact that drives atmospheric loss over time.

Lighter molecules have a higher average velocity than heavier molecules, and are lost more easily as a result. This is one reason the Earth does not have a significant amount of hydrogen or helium in its atmosphere. Jupiter, with its much stronger gravitational field, can hold on to those light gases much more effectively. Its lower temperature also helps with this (cold gases have lower molecular velocities than hot ones).

Another factor causing atmospheric loss is solar wind. The Earth's magnetic field deflects much of it, and as such has retained a thick atmosphere over time. Compare this to Mars, which has a weak magnetic field and thus has suffered much more severe atmosphere loss. Its lower gravity may have contributed to this as well.

Methane, being lighter than oxygen or nitrogen, would indeed be lost more quickly. It is also important to keep in mind that methane reacts with oxygen to form carbon dioxide and water vapor. This would also contribute significantly to decreasing the methane content of the atmosphere over time. Methane is also being continually produced by biological processes.

More information here: https://en.wikipedia.org/wiki/Atmospheric_escape
Title: Re: As methane is less dense than air, does it float out of atmosphere?
Post by: Bored chemist on 16/03/2020 21:42:14
I rather suspect that most methane is oxidised before it gets a chance to leave.
Title: Re: As methane is less dense than air, does it float out of atmosphere?
Post by: nicephotog on 15/04/2020 08:31:57
Ultimately, virtually all gas in our atmosphere will eventually be lost to space. There is a distribution of particle velocities in a gas, with most of them falling around some mean value. There is also a percentage of outlier molecules that move much more quickly than the mean value. Some of those molecules will be moving faster than the Earth's escape velocity. Those molecules will, of course, be capable of escaping the Earth's gravitational pull. This is one fact that drives atmospheric loss over time.

Lighter molecules have a higher average velocity than heavier molecules, and are lost more easily as a result. This is one reason the Earth does not have a significant amount of hydrogen or helium in its atmosphere. Jupiter, with its much stronger gravitational field, can hold on to those light gases much more effectively. Its lower temperature also helps with this (cold gases have lower molecular velocities than hot ones).

Another factor causing atmospheric loss is solar wind. The Earth's magnetic field deflects much of it, and as such has retained a thick atmosphere over time. Compare this to Mars, which has a weak magnetic field and thus has suffered much more severe atmosphere loss. Its lower gravity may have contributed to this as well.

Methane, being lighter than oxygen or nitrogen, would indeed be lost more quickly. It is also important to keep in mind that methane reacts with oxygen to form carbon dioxide and water vapor. This would also contribute significantly to decreasing the methane content of the atmosphere over time. Methane is also being continually produced by biological processes.

More information here: https://en.wikipedia.org/wiki/Atmospheric_escape
Goes in my mind I have never heard of rain being considered linked to meteorite activity by methane ignition neither forecast mm or inches from upward lightning.