The careful observer will notice that during spring and summer, in the absence of a shower, a thunderstorm, a cold front or some other sort of disturbance in the atmosphere, the air will often become wonderfully calm right around sunset. This happens because of a cooling of the air in the lowest 200-300 feet of the atmosphere.
During the day, sunlight heats the air very inefficiently, but it is very effective in heating the ground. The ground gets warm and heats the air near the ground. When the sun gets low in the sky, this heating is lost and the lower atmosphere cools at a more rapid pace, often becoming cooler than the air above. This is called a temperature inversion. Once an inversion forms, the air in this layer is separated from the forces that were producing the wind during the day, so the air becomes calm, helping to create a peaceful time at the end of the day.