Sometimes it does. It depends on weather and geography. For example, if you live in a valley, smoke settles after sunset when cool air drops down from higher elevations. This cool, dense air carries smoke from outdoor fires and woodstoves, and accumulates near the valley bottom. Although some smoke may escape through valley openings or gaps and spread to another area, most of the smoke remains trapped until the sun has warmed the ground. Then, the warm air rises and may carry the smoke out of the valley. In the winter, the days rarely warm up enough to carry away the smoke, and more smoke gets added each day. Even on summer nights, smoke can reach unhealthy levels before being cleared out the following day.