Land and water differ into the absorption and releasing of heat, the land heats up quicker than the water, and the land also cools off quicker than the water. So when the air is hotter over the land (during the day), then the air masses are moving from the sea to the land cause they are cooler and heavier. When the air is cooler over the land (during the night), then the air masses move from the land towards the water.
