The total pressure is the sum of the partial pressures, acetone and the atmosphere. If a compound is heated to its boiling point, then its vapor pressure can equal the system pressure.
If acetone is in a closed bottle, then an equilibrium will be formed so the vapor pressure and atmospheric pressure will reach an equilibrium. If the bottle is opened, then some of the acetone vapors will disperse and upset the equilibrium. As a result, more molecules can evaporate to balance the equilibrium. The evaporation takes energy from the liquid and the liquid temperature will fall. As a result, a new temperature and new equilibrium will attempt to form.
Acetone and ethanol evaporate because the vapors that form are being swept away. Compounds with high vapor pressures will evaporate more quickly in trying to maintain its equilibrium because more moles are in the vapor phase to be swept away.