North Carolina has about 150 asphalt plants, and about five new facilities are permitted each year. Many asphalt plants are portable, so they can be moved to different locations based on needs for new highways and other construction projects. Before a company can build or operate an asphalt plant, it must obtain an air quality permit and in some cases may need water quality permits. Asphalt is a paving material made from crushed rock and asphalt cement, which is a mixture of petroleum compounds produced by oil refineries.
Asphalt plants heat the asphalt cement in enclosed tanks and then combine it with crushed rock.
The asphalt is then conveyed to storage silos, where it is loaded onto trucks for delivery to construction sites for highways, parking lots and residential areas. Air emissions are created at several stages during asphalt production. Most of the emissions come from an asphalt plant's main stack. Fumes from asphalt storage and loading areas account for the remaining air emissions, collectively referred to as fugitive emissions. Asphalt production, like any process in which materials are heated or burned, can produce a range of air emissions.