As early as we've cultivated the earth and lit fires, we have been impacting air. Taking away the earth's plant cover exposes the soil to increased wind erosion.
Fires create more particles.
Depending on what we burn and how well it is burned, varying amounts of nitrous oxides, sulfur oxides, carbon dioxide and carbon monoxide are formed. And, in 1257, the Queen of England had to leave London because of poor air quality. It is not hard to imagine, then, as population densities continued to grow and the industrial revolution with its advances in technology occurred, more burning and increased production led to more of a load for the air to carry away. Of special concern is this pollutant load during temperature inversions. These inversions are natural weather events that trap warmer air next to the earth with a blanket of colder, heavier air.