In this chapter, the effects of meteorology on air pollution are discussed. The concentrations of gases and aerosol particles are affected by winds, temperatures, vertical temperature profiles, clouds, and the relative humidity. These meteorological parameters are influenced by large-and small-scale weather systems. Large-scale weather systems are controlled by large-scale regions of high and low pressure. Small-scale weather systems are controlled by ground temperatures and small-scale variations in pressure. The first section of the chapter examines the forces acting on air. The second section examines how forces combine to form winds. The third section discusses how radiation, coupled with forces and the rotation of the Earth, generates the global circulation of the atmosphere. Sections 6.4 and 6.5 discuss the two major types of large-scale pressure systems. Section 6.6 discusses the effects of such pressure systems on air pollution. The last section focuses on the effects of local meteorology on air pollution.

FORCES

Winds arise due to forces acting on the air. Next, the major forces are described.

Pressure Gradient Force

When high air pressure exists in one location and low pressure exists nearby, air moves from high to low pressure. The force causing this motion is the pressure gradient force (PGF). The force is proportional to the difference in pressure divided by the distance between the two locations and always acts from high to low pressure.