​Air Quality

Air quality is one of several elements within the human environment to be considered as part of a National Environmental Policy Act/Pennsylvania Act 120 evaluation. The NEPA requirements in regard to project-level air quality analysis are outlined in 23 Code of Federal Regulations (CFR), Part 771.

The Environmental Protection Agency established standards for a number of air pollutants in the Clean Air Act (CAA). The CAA has established specific procedures and limitations for evaluating transportation projects in regions of the United States, called nonattainment or maintenance areas that have not met these standards. Conformity regulations require PennDOT to assess the potential air quality impacts of all regionally significant planned and programmed transportation projects on the natural and human environment.

The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are the "criteria" air pollutants. The six pollutants are carbon monoxide, ozone, PM2.5 or PM10, nitrogen oxides (NOx), sulfur dioxide (SO2), and lead. Many of these are caused by transportation-related sources. In addition, other transportation-related pollutants of concern, which are not criteria pollutants, include Mobile Source Air Toxics (MSATs) and Greenhouse Gases (GHG).

Air quality analyses may be conducted at the regional and/or project level depending on the characteristics of the project and the attainment status for the project location. Ozone and PM2.5 are evaluated as part of the regional conformity analyses as applied to the TIP and Long Range Transportation Plan (LRTP) process. PM 2.5 (in addition to regional application), CO, and MSATS are typically addressed at the project level within the NEPA process.

Pennsylvania currently has nonattainment and maintenance areas for ozone and PM2.5.