Asphalt (bitumen) may contain very high vapor phase concentrations of hydrogen sulfide (H₂S). H₂S concentrations can easily exceed 20,000 ppm in the headspace of asphalt storage tanks; these concentrations present an immediate danger to personnel exposed through transport or handling of this product. This high concentration is due to the concentration of sulfur compounds in asphalt feedstock, such as vacuum tower bottoms, elevated storage temperatures, and the propensity of H₂S to leave the liquid phase of asphalt in favor of the vapor phase. Moreover, unlike finished fuels such as gasoline and diesel, asphalt does not go through any sweetening processes during production. 

High production and storage temperatures limit the choices for effective H₂S scavengers for asphalt. Nalco Water has more than 20 years of experience successfully producing and applying metal-based scavengers for asphalt. These metal-based additives have an increased capacity to scavenge H₂S versus conventional scavengers and can be applied at the elevated temperatures typical of asphalt production and storage. The Nalco Water patented H₂S scavengers for asphalt have been shown to have no detrimental impact on finished asphalt performance grade specifications.