Final answer:
Decreased air pollutants since 1970 are due to more pollution controls, technological advancements, and environmental policies, despite population and economic growth. Air quality improvements stem from initiatives including technology to scrub emissions and shifts to nonpolluting energy sources.
Step-by-step explanation:
Air pollutants have decreased significantly since 1970 primarily due to the implementation of more pollution controls. Despite an increase in population and economic growth, the United States has seen a notable decline in emissions of key air pollutants. This reduction can be attributed to a variety of anti-pollution policies, which include the adoption of better technology to scrub emissions from sources like coal-fired power plants and a shift in manufacturing capacity to other countries, albeit raising concerns about global impacts.
It is also relevant to mention that improved technologies and increased environmental awareness have played a role in reducing air pollution. Furthermore, initiatives to curb air pollution have included transitioning to nonpolluting energy sources and conservation measures to use less energy, contributing to the overall reduction in emissions.