Other programs create requirements for vehicle fuels, industrial facilities, and other technologies and activities that impact air quality.

Newer programs tackle specific problems, including acid rain, ozone layer protection, and climate change.

Although many parts of the statute are quite detailed, others set out only the general outlines of the law's regulatory programs, and leave many key terms undefined.

Initially, EPA did not list lead as a criteria air pollutant, controlling it through mobile source authorities, but it was required to do so after successful litigation by Natural Resources Defense Council (NRDC) in 1976 (43 FR 46258).

L. 101–549 Title III) codified EPA's list, and required creation of technology-based standards according to "maximum achievable control technology" (MACT).

[9] The 1990 amendments (adding CAA § 112(d-f)) also created a process by which EPA was required to review and update its NESHAPs every eight years, and identify any risks remaining after application of MACT, and develop additional rules necessary to protect public health.

Under Title VI, EPA runs programs to phase out ozone-destroying substances, track their import and export, determine exemptions for their continued use, and define practices for destroying them, maintaining and servicing equipment that uses them, identifying new alternatives to those still in use, and licensing technicians to use such chemicals.

The federal government has regulated the chemical composition of transportation fuels since 1967, with significant new authority added in 1970 to protect public health.

[25] One of EPA's earliest actions was the elimination of lead in U.S. gasoline beginning in 1971,[26] a project that has been described as "one of the great public health achievements of the 20th century.

It required large businesses to address pollutants released into the air, measure their quantity, and have a plan to control and minimize them as well as to periodically report.

The agency has also proposed a two-phase program to reduce greenhouse gas emissions for medium and heavy duty trucks and buses.

The law recognizes that states should lead in carrying out the Clean Air Act, because pollution control problems often require special understanding of local conditions such as geography, industrial activity, transportation and housing patterns.

[53] The federal government also assists the states by providing scientific research, expert studies, engineering designs, and money to support clean air programs.

However, in September 2019, President Donald Trump attempted to revoke this waiver, arguing that the stricter emissions have made cars too expensive, and by removing them, will make vehicles safer.

[56] In March 2022 the Biden administration reversed the Trump-era rule, allowing California to again set stricter auto emissions standards.

At the time, the primary federal agencies interested in air pollution were the United States Bureau of Mines, which was interested in "smoke abatement" (reducing smoke from coal burning), and the United States Public Health Service, which handled industrial hygiene and was concerned with the causes of lung health problems.

[61][60] This enabled the federal government to increase its activities to investigate enforcing interstate air pollution transport, and, for the first time, to perform far-reaching ambient monitoring studies and stationary source inspections.

To implement the strict amendments, EPA Administrator William Ruckelshaus spent 60% of his time during his first term on the automobile industry, whose emissions were to be reduced 90% under the new law.

The 1977 Amendments primarily concerned provisions for the Prevention of Significant Deterioration (PSD) of air quality in areas attaining the NAAQS.

Other revisions included provisions regarding stratospheric ozone protection, increased enforcement authority, and expanded research programs.

The provisions aimed at reducing sulfur dioxide emissions included a cap-and-trade program, which gave power companies more flexibility in meeting the law's goals compared to earlier iterations of the Clean Air Act.

[66] Further amendments were made in 1990 to address the problems of acid rain, ozone depletion, and toxic air pollution, and to establish a national permit program for stationary sources, and increased enforcement authority.

Reviewing his tenure as EPA Administrator under President George H. W. Bush, William K. Reilly characterized passage of the 1990 amendments to the Clean Air Act as his most notable accomplishment.

The Inflation Reduction Act, the budget reconciliation bill signed by President Joe Biden in August 2022, amends the Clean Air Act to allow the EPA to administer $27 billion in grants to green banks nationwide, through a competitive funding mechanism to be called the Greenhouse Gas Reduction Fund.

[75] According to a 2022 review study in the Journal of Economic Literature, there is overwhelming causal evidence that shows that the CAA improved air quality.

[79] Mobile sources including automobiles, trains, and boat engines have become 99% cleaner for pollutants like hydrocarbons, carbon monoxide, nitrogen oxides, and particle emissions since the 1970s.

[97] Research shows that the leading air pollutant in the region is known as PM 2.5, or fine particulate matter, and causes health issues in pregnant women exposed to it, such as more severe asthma, decreased FEV1, compromised immunity, and an increased risk of premature birth.

[99] Other symptoms that come from exposure to PM 2.5 include chronic bronchitis, reduced lung function in children, and heart and lung-related hospitalizations that can potentially lead to premature death especially if the individual has previous health concerns.

Organizations such as the California Air Resources Board (CARB) have recommended that more sufficient regulations be implemented in the San Joaquin Valley to reduce toxic emissions into the atmosphere.

[105] High levels of exposure to air pollution is linked to several health conditions, including asthma, cancer, premature death, and infant mortality, each of which disproportionately impact minority and low-income communities.