Black buildup is a term used to describe the accumulation of SOOT, which is a black or dark gray powdery or flaky substance made up of carbon particles. It is often found in areas where there is a lot of burning of fossil fuels, such as in industrial areas or near power plants. SOOT can also be created by burning wood or other organic materials. Black buildup can cause air pollution and health problems, and it is important to reduce its presence in the environment.