Credit: Adapted from diagrams created by the Environmental Protection Agency
| Figure 1. Formation of particulate matter. The top diagram shows particles that are directly emitted into the air. They come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood. The bottom diagram shows how other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes. |