Why does air rise at the equator but sink at the poles?

The Earth tilts on its axis which causes major differences to the amount of light that reaches the poles and extremes of Northern and Southern latitudes. The equatorial region is virtually unaffected by the seasonal tilt of the Earth and as such receives a large amount of light all year round.

Due to this the polar regions are significantly colder than the equatorial regions.

When a substance is heated the particles of that substance receive more kinetic energy; move more rapidly; move further apart; and therefore expand. When substances expand like this there are less particles per unit area and therefore the substance becomes less dense.

A less dense substance will float on top of a more dense substance.

Air is heated at equatorial regions and therefore rises due to decreased density.

Air is cooled at polar regions and therefore sinks due to increased density.