In this question about the amount of sulfuric acid in the atmosphere of Venus it is calculated that the amount of water in it's atmosphere is $9.6 \times 10^{15} \text{ kg }$ H$_2$O.
But the calculation didn't account for the difference in molar mass between water and CO$_2$, the main constituent of the atmosphere, so the amount above needs to be multiplied by a factor 18/44, giving a total amount of $3.93 \times 10^{15} \text{ kg }$ H$_2$O instead.
It should be noted that water vapor measurements by entry probes below the clouds have provided conflicting results, but that a consensus has emerged toward a mixing ratio of 30 +/- 10 ppm, approximately constant in the whole 0-45 km range. (Composition of the atmosphere of Venus below the clouds, chapter 9)
Thus the total amount of water would then become about $5.9 \times 10^{15} \text{ kg }$.

In one of the answers to that question it is calculated that there is a total of $9 \times 10^{13} \text{ kg }$ H$_2$SO$_4$ in the clouds of Venus.
Assuming that at least 75% by weight of the droplets is sulfuric acid, this means that no more than $2.25 \times 10^{13} \text{ kg }$ H$_2$O is in those clouds.

So almost all of the water must be outside the clouds !

The figure on page 14 of the dissertation of Yeon Joo Lee shows that beneath the cloud layers there is a thin haze region which has a thousandfold less mass loading than the clouds above it, so the amount of water there is negligible.

So almost all of the water must be above the clouds !

Is this true or must there be some miscalculations ?

Is there any publication that can confirm the question ?

  • 1
    $\begingroup$ Could the water not simply be vapour rather than clouds of droplets? $\endgroup$ May 26, 2018 at 18:33
  • $\begingroup$ @SteveLinton Yes, could be, i don't know. So i've changed the question again ! $\endgroup$
    – Cornelis
    May 26, 2018 at 19:14

1 Answer 1


No !

The conclusion that the amount of water in the haze region is negligible is false !

Figure 4 of the article The Recent Evolution of Climate on Venus from Bullock and Grinspoon shows the abundances of H$_2$SO$_4$ and H$_2$O in the cloud region of the atmosphere of Venus.

Fig. 4 Bullock & Grinspoon 2001 Venus aerosols

The dashed line for H$_2$O there shows that above the H$_2$SO$_4$ production region there is less than 4 ppm H$_2$O, gradually growing to above 26 ppm below the lower cloud boundary.

So there's much less water above than below the clouds whereas the conclusion in the question that most of the water in the atmosphere is outside the clouds looks justified.

So almost all of the water in the atmosphere of Venus must be below the clouds !

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    $\begingroup$ Minor point. $\text{H}_2\text{SO}_4$ gas appears mislabeled. Seems to be $\text{H}_2\text{SO}_4$ vapor in the predominantly $\text{CO}_2$ gas. $\endgroup$ Sep 18, 2020 at 15:20
  • $\begingroup$ @OscarLanzi Yes, with a concentration above 80 %, the sulfuric acid will loose no water with the measured pressure and temperature there, and will be still in the liquid phase. See Fig. 6 of this paper: personal.psu.edu/mrh318/Gmitro-Vermeulen-AICE-1964.pdf $\endgroup$
    – Cornelis
    Sep 19, 2020 at 10:20

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