Environmental Guidance Documents

NEPA Process Guidance for Federal Aid Projects

Air Quality

Clean Air Act

The Clean Air Act, signed into law in 1963, was designed to control air pollution on a national level.  The US Environmental Protection Agency (USEPA) is the federal agency that oversees the enforcement and development of air quality regulations.  The Clean Air Act of 1970 expanded the federal directive, requiring comprehensive federal and state regulations for both stationary (industrial) pollution sources and mobile sources (transportation). The Clean Air Act was last amended in 1990; the amendment included the regulation of toxic emissions from transportation projects.  The State of Arizona has implemented the federal air quality control standards and enacted control measures that are specific to the state.  Three local governments; Maricopa County, Pima County and Pinal County have their own air pollution control programs and operate pursuant to an agreement with the Arizona Department of Environmental Quality (ADEQ).  In addition, the Gila River Indian Community has tribal authority for air quality planning and management, and several other Arizona tribes have air quality programs.

National Ambient Air Quality Standards

The USEPA set National Ambient Air Quality Standards (NAAQS) (40 CFR part 50) under authority of the Clean Air Act (42 USC 7401) for pollutants considered harmful to public health and the environment.  The Clean Air Act identifies two types of NAAQS, Primary and Secondary.  Primary standards provide public health protection, including protecting the health of sensitive populations such as people with respiratory ailments, children, and the elderly.  Secondary standards provide protection for the good of the public, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.  An area that meets a given standard is referred to as an attainment area and an area that does not meet a given standard is referred to as a nonattainment area. Maintenance areas are former nonattainment areas that meet the NAAQS but must demonstrate continuing attainment through a maintenance plan and control measures.

Mobile Source Air Toxics

In 2001, USEPA issued its first Mobile Source Air Toxics Rule, which identified 21 mobile source air toxic (MSAT) compounds as being hazardous air pollutants that required regulation. Then in February 2007, USEPA issued a second MSAT Rule which supported the findings in the first rule and provided additional recommendations on compounds having the greatest impact on public and environmental health. Further information regarding MSAT evaluation, conducted during project development and alternative analysis, can be found in FHWA’s Interim Guidance on Air Toxic Analysis in NEPA Documents.

NEPA Process

EPG evaluates ADOT projects to ensure that all projects and operations comply with federal, state and local air quality laws and regulations.

During project planning, air quality analysis begins to determine if the project will cause or contribute to a violation of the NAAQS. Specialized air modeling may be conducted for those projects in nonattainment or maintenance areas that increase traffic capacity or have changes in the vertical and/or horizontal alignment.  The results of the air quality analysis will be included in a CE, EA or EIS NEPA document.