In the daytime, land heats rapidly, which heats the air above it. The water temperature remains relatively constant. The air over the heated land surface rises producing low pressure compared with the pressure over water. The resulting pressure gradient produces a surface flow off the water toward land. This circulation can extend to a considerable distance inland. Initially, the flow is onto the land, but as the breeze develops, the Coriolis force gradually shifts the direction so that the flow is more parallel to the land mass. After sunset and several hours of cooling by radiation, the land mass is cooler than the water temperature. Then, the reverse flow pattern develops, resulting in a wind off the land. During a stagnating high-pressure system when the transport and dispersion of pollutants are reduced, this short-period, afternoon increase in airflow can prevent the critical accumulation of pollutants.
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