A colorless, flammable liquid with the formula C₉H₁₂. It occurs naturally in coal tar and petroleum crude oil and therefore ends up in gasoline. It is a major component (typically 40%) of a petroleum refinery distillation fraction known as the C9 aromatic fraction. Oil refineries produce large amounts of this substance each year. Most of the C9 fraction is usually added directly to gasoline. Exposure to 1,2,4 trimethylbenzene can occur in the workplace or in the environment following releases to air, water, land, or groundwater. Vehicle emissions are a major anthropogenic source of 1,2,4-trimethylbenzene, due to its widespread occurrence in gasoline. Once in air, it breaks down and contributes to photochemical smog when it reacts with other volatile substance. This compound is also used by industries as chemical raw materials, paint thinners, and solvents.