Sulfur dioxide is composed of one sulfur atom and two oxygen atoms. Each oxygen is conected to the sulfur by a double covalent bond.
The pink atoms represent the oxygen and the purple atom represents the sulfur. The molecular geometry of sulfur dioxide is bent.
Oxygen is highly electronegative.
Sulfur is much less electronegative.
This results in polar bonds between the oxygen atoms and sulfur atom.
Because of the molecule's bent shape and the electronegativity difference between sulfur and oxygen, SO2 is a polar molecule.