<u>Lead</u><u> </u>is a naturally occurring metal found in the environment as well as manufactured in products. The major source of this metal has historically been fuels in on-road motor vehicles such as cars and trucks, and industrial sources.
<h3>Lead: An Air Pollutant</h3>
Both naturally occurring in the environment and used in manufactured goods are the metal lead. In the past, industrial sources and fuels used in on-road motor vehicles (such as cars and trucks) have been the main sources of lead emissions. Lead emissions from the transportation industry rapidly reduced by 95% between 1980 and 1999 thanks to regulatory measures in the U.S. to remove lead from gasoline for on-road motor vehicles, while lead levels in the air decreased by 94% over the same period. The areas closest to lead smelters typically have the greatest airborne lead concentrations today. Today, the processing of ores and metals as well as piston-engine aircraft using leaded aviation gasoline are the main sources of lead emissions into the atmosphere.
Carbon-12 is an isotope of carbon. The atomic mass of carbon-12 atom is equal to . The atomic mass of carbon in the period table is not 12.00 amu but is 12.01 amu.
