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Thread: Venus clouds may be less acidic that we thought

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    Venus clouds may be less acidic that we thought

    I've just been looking a paper from Cornell University, written in January this year, about the quantities of SO2 (sulfur dioxide) and H2O (water vapor) at various levels of the atmosphere of Venus. The researchers note that considering the quantities detected near the surface, the quantities in the cloud level are anomalously low. They suggest several different hypotheses to explain this anomaly.

    One hypothesis involves SO2 being absorbed into the sulfuric acid droplets. This wouldn't work if the droplets were pure sulfuric, but would work if they also contain hydroxide salts. These salts would mean higher pH -- i.e. less extreme acidity. The paper finds (page 31) that the acidicity implied by this hypothesis is "within the range where known acidophiles can thrive". Though the acidophiles might still be prevented for thriving by the low concentration of H2O, an issue distinct from pH.
    Last edited by Colin Robinson; 2021-Apr-02 at 05:13 AM.

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    If the SO2 was oxidised to SO3, it would then be absorbed by sulphuric acid. This is the Contact Process for manufacturing the acid.

    Where are these alkaline salts coming from, on a planet surface exposed to sulphuric acid for millions of years?

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    Quote Originally Posted by kzb View Post
    If the SO2 was oxidised to SO3, it would then be absorbed by sulphuric acid. This is the Contact Process for manufacturing the acid.
    Yes and it's understood that some SO2 in the atmosphere of Venus does get oxidised to SO3 and H2SO4. The limiting factor is low level of atmospheric O2.

    Where are these alkaline salts coming from, on a planet surface exposed to sulphuric acid for millions of years?
    The basaltic minerals on the surface of Venus contain substantial calcium oxide (CaO), magnesium oxide (MgO), and potassium oxide (K2O), all of which are alkaline.

    Surface minerals are unlikely to be directly exposed to sulfuric acid, since high temperature near the surface breaks down the sulfuric into SO2, O2 and H2O — the reverse reaction to the one you mentioned.

    Even so, the co-existence of acidic sulfur compounds in the atmosphere and alkaline oxides on the surface is something of a puzzle.

    One theory is that the current amount of atmospheric SO2 and sulfuric acid is a comparatively new state of affairs, due to recent volcanic activity on a massive scale.
    Last edited by Colin Robinson; 2021-Apr-13 at 12:09 AM.

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    The terrestrial bacterium Acidithiobacillus ferrooxidans lives in a very acidic environment - the Venusian clouds are composed of corrosive sulfuric acid. This persistent baby absorbs carbon dioxide and nitrogen from the air, and receives energy by oxidizing iron, hydrogen and sulfur - there is plenty of all of this in the atmosphere of Venus. Other microorganisms are also known that, in theory, would not have disappeared over the neighboring planet. Some of them are so severe that in difficult conditions they themselves produce sulfuric acid - and nothing.

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    Quote Originally Posted by cannongray View Post
    Other microorganisms are also known that, in theory, would not have disappeared over the neighboring planet.
    Disappeared? We have no evidence they were ever there.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Colin Robinson View Post
    Yes and it's understood that some SO2 in the atmosphere of Venus does get oxidised to SO3 and H2SO4. The limiting factor is low level of atmospheric O2.
    .
    Is it possible for the reaction

    CO2 + SO2 = SO3 + CO

    to occur in the Venus atmosphere, exposed to UV and high temperature?

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    Quote Originally Posted by kzb View Post
    Is it possible for the reaction

    CO2 + SO2 = SO3 + CO

    to occur in the Venus atmosphere, exposed to UV and high temperature?
    Interesting point...

    I've just had another look at the paper by the Cornell University people (linked in the opening post of this thread).

    They mention reactions like that — CO2 giving up oxygen atoms, which oxidise SO2 leading to formation of H2SO4. But they make the point that formation of H2SO4 in this way is limited by availability of water molecules.

    However, formation of SO3 (as distinct from H2SO4) presumably doesn't require water molecules.

    To see if that's what is happening, you'd have to look at questions like the stability of SO3 (as distinct from H2SO4 ) in Venus atmospheric conditions, how detectable is it, and what levels are detected?

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    Quote Originally Posted by Colin Robinson View Post
    Interesting point...

    I've just had another look at the paper by the Cornell University people (linked in the opening post of this thread).

    They mention reactions like that — CO2 giving up oxygen atoms, which oxidise SO2 leading to formation of H2SO4. But they make the point that formation of H2SO4 in this way is limited by availability of water molecules.

    However, formation of SO3 (as distinct from H2SO4) presumably doesn't require water molecules.

    To see if that's what is happening, you'd have to look at questions like the stability of SO3 (as distinct from H2SO4 ) in Venus atmospheric conditions, how detectable is it, and what levels are detected?
    There's LOTS of CO2 available.

    Also there is 17ppm of CO in the atmosphere, perhaps this is where it comes from.

    SO3 is absorbed by concentrated sulphuric acid in the contact process, there is no "extra" water required in addition to what was needed to form H2SO4 in the first place. But I suppose we then have to ask can "oleum" be detected?

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    Quote Originally Posted by kzb View Post
    There's LOTS of CO2 available.
    True...

    Also there is 17ppm of CO in the atmosphere, perhaps this is where it comes from.
    17 ppm of CO...

    As the paper mentions, the measured concentration of SO2 at 40 km above the surface is above 100 ppm, but 80 km above the surface it is several orders of magnitude lower — between 1 and 100 ppb (note: parts per billion, not parts per million).

    So what happens to SO2 molecules diffusing upwards?

    If most of them get oxidised by the reaction CO2 + SO2 -> SO3 + CO, the resulting CO concentration would logically be a lot more than 17 ppm, surely?

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    Quote Originally Posted by Colin Robinson View Post
    True...



    17 ppm of CO...

    As the paper mentions, the measured concentration of SO2 at 40 km above the surface is above 100 ppm, but 80 km above the surface it is several orders of magnitude lower — between 1 and 100 ppb (note: parts per billion, not parts per million).

    So what happens to SO2 molecules diffusing upwards?

    If most of them get oxidised by the reaction CO2 + SO2 -> SO3 + CO, the resulting CO concentration would logically be a lot more than 17 ppm, surely?
    Is it ppm by volume or mass? The molecular mass ratio is 68/28.

    Anyhow, I was just wondering out loud if these planetary scientists have heard of the contact process.

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    Quote Originally Posted by kzb View Post
    Is it ppm by volume or mass?
    I think it means ppm by volume, as this is the usual measure for concentrations of gases in an atmosphere.

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