What will happen if there are air bubbles are introduced into the barometer tube?
The height of the mercury column will decrease.
Mercury barometer works on the principle: The atmospheric pressure is equal to the pressure due to the mercury column.
If air bubbles are introduced to the tube, they exert some pressure. In this case, the atmospheric pressure will be equal to sum of the pressures due to air inside the tube and the mercury column.
Since atmospheric pressure is constant at a place, the height of the mercury column decreases as air is added to the barometer tube.
Mercury does not react violently with air under normal conditions.