Areas in Maryland that do not meet the 8-hour ozone standard have not yet been identified. Ground-level ozone is formed from the chemical reaction of volatile organic compounds and nitrogen oxides in the presence of sunlight. The primary sources of these pollutants are motor vehicles, utilities and industries, and numerous small sources such as gas stations, and farm and lawn equipment. Sulfur dioxide is mostly emitted from industrial and utility sources. Particulate matter comes from industrial processes, motor vehicles, wood burning, and dust from roads, stockpiles, construction, and agricultural sites.
Nitrogen dioxides mostly result from burning fuels in utilities, industries, and motor vehicles.
Lead is emitted by transportation sources using leaded fuels, coal combustion sources, and smelters. Lead emissions have dramatically decreased since 1980 due in large part to the elimination of the sale of leaded gasoline to the general public.