Under any pressure conditions is it possible ? If not then is there no water vapour present in places where temperature drops to -10 degree celcius ?

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    $\begingroup$ Yes it is possible, albeit to a little extent. $\endgroup$ – Ivan Neretin Aug 31 '18 at 6:21
  • $\begingroup$ Welcome to Chemistry.SE! Questions are the central focus of this site, but we ask that questions demonstrate an attempt to solve/understand the question to maintain quality. Please take a minute to look over the help center and tour page to better understand our guidelines and question policies. $\endgroup$ – A.K. Aug 31 '18 at 11:04

As @Ivan Neretin comments just a little. At $-10$ C the vapour pressure is $\approx 260 $ Pa (Pascal) where $1\text{ atm} = 101325$ Pa. Even at $-100$ C there is some absolutely minute amount, $0.0014$ Pa.

The reason is that there is still some energy around even at these low temperatures. The chance (probability) that there is enough energy to propel a molecule into the gas phase, decreases, of course, as the temperature falls. It does so very rapidly as it is given by the Boltzmann distribution which decrease exponentially with energy at any fixed temperature.; $prob(E)\sim \exp(-E/(k_BT))$ where $E$ is the energy/ molecule needed to put the molecule into the gas phase and $k_B$ the Boltzmann constant.


Snowflakes are ice crystals that are formed directly from water vapor present in the air when the ambient temperature is below 0 Celsius. So it is quite common to have water vapor present in the air at below-freezing temperatures. Snow formation occurs on a gigantic scale every day, somewhere in the world.

Sometimes you can observe ice and snow slowly disappear even during a cold snap in winter when temperatures remain below freezing over a long period of time. In this case, the ice sublimes directly into the vapor phase. You could also observe this process in the laboratory on a small scale by placing ice in a vacuum chamber and pumping on it to a high vacuum.


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