Is there sulfuric acid rain on Venus?

[m1omg]

Is there any sulfuric acid rain on Venus?It imo could, because there are large storms and if the boiling point of sulfuric acid under 1 atmosphere, then using this boiling point calculator;http://www.trimen.pl/witek/calculators/wrzenie.html I calculated that boiling point of H2SO4 under pressure of the atmosphere on the surface of Venus (91 atm.) is 775 degress Celsius (under 1 atm. it is 338 degress), but this is above critical temperature so real boiling point is about 663 degress I dont know critical pressure in Wikipedia it is only ?, but on the surface of Venus there is a temperature of about 450 degress so sulfuric acid can be liquid and so there can be rain of sulfuric acid, is that right or I am wrong at this?

[grant hutchison]

You need to be a little careful using calculators like that: extrapolating from one atmosphere to 91 atmospheres is a serious leap. In particular, a phase-change calculation using only pressure, temperature and latent heat is often made on the assumption that the volume change associated with the phase change is constant; this is certainly far from true when dealing with vaporization across a 90-fold variation in pressure! The fact that you're getting an answer above the critical temperature is also a flag telling you that your answer is unphysical.

I've no idea what the detailed thermodynamics are in this case, but I know that sulphuric acid rain on Venus is said to form virga, rain that evaporates before it reaches the surface. For instance, John Lewis writes in Physics and Chemistry of the Solar System (Revised Ed.) that sulphuric acid rain falls into regions at which it evaporates (this needn't involve temperatures that exceed the local boiling point), after which the gaseous H2SO4 decomposes thermally into H2O and SO3.

Grant Hutchison

[m1omg]

Why it evaporates before reaching the surface it the temperature doesnt exceed the boiling point of H2SO4 ?What is the precise boiling point of H2SO4 at 91 atm.?It at last must reach the tops of the highest mountains.

[grant hutchison]

Why it evaporates before reaching the surface it the temperature doesnt exceed the boiling point of H2SO4 ?Why does water evaporate on Earth, at temperatures far below its boiling point?
If the vapour pressure of the gas phase is lower than the saturated vapour pressure for the ambient temperature, the liquid will evaporate until the saturated vapour pressure is reached. So if H2SO4 liquid falls into regions where the H2SO4 "humidity" is low, the liquid will evaporate. And because H2SO4 gas breaks down thermally at temperatures that prevail some distance below Venus' clouds (but some distance above its surface), the partial pressure of the H2SO4 gas phase in the mid-atmosphere can never rise high enough to prevent the descending liquid drops from evaporating while they are still falling. The clouds are at ~50km altitude, and the evaporation of the raindrops is predicted to be complete by ~25km altitude, according to a diagram in Lewis' book.

Grant Hutchison

[m1omg]

But should at least some drops fall on the highest points of the Venus's surface?

[m1omg]

And is there at least some sulfuric acid in the lower layer of the atmosphere?If it is,does at least some fog form?

[m1omg]

Why does water evaporate on Earth, at temperatures far below its boiling point?
If the vapour pressure of the gas phase is lower than the saturated vapour pressure for the ambient temperature, the liquid will evaporate until the saturated vapour pressure is reached. So if H2SO4 liquid falls into regions where the H2SO4 "humidity" is low, the liquid will evaporate. And because H2SO4 gas breaks down thermally at temperatures that prevail some distance below Venus' clouds (but some distance above its surface), the partial pressure of the H2SO4 gas phase in the mid-atmosphere can never rise high enough to prevent the descending liquid drops from evaporating while they are still falling. The clouds are at ~50km altitude, and the evaporation of the raindrops is predicted to be complete by ~25km altitude, according to a diagram in Lewis' book.

Grant Hutchison

Ok, thank you, I understand that now, it is because the clouds are enough high and temperature high enough to eveporate them before reaching the surface.

But what about H2SO4 fog?

[grant hutchison]

But should at least some drops fall on the highest points of the Venus's surface?The highest points don't reach the 25km altitude mention in Lewis' book. You're of course welcome to speculate about unusual conditions during Venusian cloudbursts.

And is there at least some sulfuric acid in the lower layer of the atmosphere?If it is,does at least some fog form?No sulphuric acid: it breaks down thermally under surface conditions, if we believe Lewis (and I do). Fog is just cloud at surface level: it requires high relative humidity, and in the absence of gaseous sulphuric acid you won't see condensation of liquid droplets.

Grant Hutchison

[m1omg]

So no fog or haze on the surface of Venus?
And if there is some volcanic eruption nearby?

[grant hutchison]

So no fog or haze on the surface of Venus?Not of water or sulphuric acid, no.

And if there is some volcanic eruption nearby?I'm missing the connection with fog.

Grant Hutchison

[m1omg]

Or haze.Or shouldn't volcanic eruption temporarily raise the concentration of H2SO4 near the surface locally?

[grant hutchison]

Or haze.Or shouldn't volcanic eruption temporarily raise the concentration of H2SO4 near the surface locally?According to Lewis, it's sulphur oxides and hydrogen sulphide that are expected to come out of Venusian volcanoes. The sulphuric acid forms in the high clouds and is destroyed when it falls back towards the surface.

Grant Hutchison

[m1omg]

Ok so no H2SO4 fog at the surface.But is there at least some sort of haze?

[grant hutchison]

You seem to have some sort of vested interest in generating fog or haze at Venus' surface. Maybe you should try a Google search using these terms. You might turn up some exotic chemical process that'll meet your requirements.

Grant Hutchison

[Noclevername]

Ok so no H2SO4 fog at the surface.But is there at least some sort of haze?


There's no evidence of such, that I'm aware of. Just a little dust blowing, which is probably very sluggish. Are you asking if it's possible, or if it actually happens?

[neilzero]

According to my hand book SO3 melts at 18 degrees c and boils at 44 degrees c. The boiling point is likely much higher at 91 atmospheres. The acid droplets have plenty of time to evaporate as the terminal velocity of the falling droplets may be less than one kilometer per hour in the thick atmosphere at an altitude of 25 kilometers.
Should I conclude that the atmosphere of Venus is several parts per million of water vapor at an altitude of 25 kilometers, because of decomposing H2SO4? Does it take seconds or hours for a large drop of sulphereic acid to lose it's water at an altitude of 10 kilometers, if any falls that low? Does sulpheric acid vapor decompose quickly, in spite of the large amount of heat needed to separate the water? SO3 is sulpher trioxide. Neil

[cran]

I seem to recall mention of a lead sulphide "snow" on the higher peaks ...
that was some years ago, something to do with highly reflective surfaces ...

I don't suppose that would suit?

perhaps some kind of lead compound (or silicon compound) could exist as a hazy vapour near the surface?

I've not heard of any, though ...

[grant hutchison]

I seem to recall mention of a lead sulphide "snow" on the higher peaks ...
that was some years ago, something to do with highly reflective surfaces ...Some more on the likely compounds involved appears here (http://solarsystem.wustl.edu/heavy%20metal%20snow%20on%20Venus.pdf) (pdf).

Grant Hutchison

[Swift]

There's no evidence of such, that I'm aware of. Just a little dust blowing, which is probably very sluggish. Are you asking if it's possible, or if it actually happens?
This website (http://www.mentallandscape.com/Venus_Venera.htm) has some impressively reprocessed photos taken by the Russian landers. Though the photos don't show a lot of distance (they are more looking down at the ground), there is no evidence of haze (at that particular place and time). Until someone revisits, we probably won't know more.

[JESMKS]

It should be feasible to design, construct and place a balloon in the Venusian atmosphere that would float below the cloud level. The Russian pictures look like it is fairly clear below the clouds. Such a balloon could provide detailed surface pictures, wind information, climate information and many other observations.

[beech]

The critical point of water is 374.15C at 22120 kPa. If the sulfuric acid is 10%, this might be 25 degrees higher. In this case, the mixture can only exist as superheated vapour. Above the critical temperature AND critical pressure a pure substance exists as a FLIUD. Fliud water might exist, coming from "smokers" more than two miles deep in the Atlantic ocean ridge.

The composition of the substance has to be known, before you can even speculate about misting or precipatation.