Which option correctly lists the six common criteria air pollutants regulated under the U.S. Clean Air Act and a major source for each?

• A. Ground-level ozone — vehicle exhaust and other VOC/NOx sources; Particulate matter (PM) — construction and combustion; Carbon monoxide — motor vehicles; Sulfur dioxide — coal-fired power plants and oil refineries; Nitrogen dioxide — vehicle emissions; Lead — legacy lead in old paint and some industrial processes.
• B. Ground-level ozone — industrial solvents; PM — agriculture; Carbon monoxide — residential wood burning; Sulfur dioxide — natural sulfur emissions; Nitrogen dioxide — lightning; Lead — volcanic ash.
• C. Ground-level ozone — NOx and VOCs; PM — windblown dust; Carbon monoxide — airplanes; Sulfur dioxide — natural volcanic emissions; Nitrogen dioxide — soil gases; Lead — plastics contamination.
• D. Ground-level ozone — vehicle exhaust; PM — construction; Carbon monoxide — motor vehicles; Sulfur dioxide — volcanic emissions; Nitrogen dioxide — industrial emissions; Lead — natural background.

Answer: (A)

The question tests knowledge of the six common criteria air pollutants and typical sources that contribute to them under the Clean Air Act. Ground-level ozone is a secondary pollutant formed in the presence of sunlight from nitrogen oxides and volatile organic compounds, so a major source is vehicle exhaust and other VOC/NOx sources. Particulate matter comes directly from activities like construction and combustion processes, making those good representative sources. Carbon monoxide is produced mainly by incomplete combustion, with motor vehicles as a primary source. Sulfur dioxide mainly results from burning sulfur-containing fuels, especially in coal-fired power plants and oil refineries. Nitrogen dioxide is formed in combustion, with vehicle emissions being a leading source. Lead today largely comes from legacy lead in older paint and certain industrial processes. This combination aligns with how these pollutants are regulated and where emissions typically originate, which is why this option is the best fit.