Evaporation can occur at any pressure, but the rate at which it takes place is influenced by the pressure exerted on the liquid. Evaporation is the process by which molecules at the surface of a liquid gain enough kinetic energy to transition into the gas phase. As temperature increases, the average kinetic energy of the liquid molecules increases, resulting in more frequent and energetic collisions that can overcome intermolecular forces and escape from the liquid surface.
At higher pressures, the partial pressure of the gas above the liquid increases, which can hinder the escape of vapor molecules from the liquid surface. This can reduce the rate of evaporation. Conversely, at lower pressures, the partial pressure of the gas above the liquid decreases, allowing for easier escape of vapor molecules and thus increasing the rate of evaporation.
However, it's important to note that evaporation can occur even at low pressures, such as in a vacuum, where the pressure is significantly below atmospheric pressure. In fact, in a vacuum, the boiling point of a liquid is lowered, and evaporation can happen more readily.
So, while the pressure can influence the rate of evaporation, evaporation itself can occur over a wide range of pressures, from high to low, depending on the temperature and the specific conditions of the system.