In some ways, air pollution is kind of a part of life. There are roughly 200 regulated hazardous air pollutants in the United States, many with names I can barely pronounce. But they’re obviously not all gone, because that secondary benefit of air quality turned into the primary benefit as environmental rules about air pollution became stricter. There are really just two major transport processes for air pollution. Gravity also affects air pollution, but it doesn’t have a significant effect except on heavier-than-air particulates.