Transportation & Toxic Air Pollutants

Pollutants are generated by a wide variety of sources and enter the air, water, and soil through different media. Toxic air pollutants-also known as Hazardous Air Pollutants or HAPs-are those that are known to cause or suspected of causing cancer or other serious health ailments.

The Clean Air Act Amendments of 1990 listed 188 HAPs and addressed the need to control toxic emissions from transportation. In 2001, EPA issued its first Mobile Source Air Toxics Rule which identified 21 mobile source air toxic compounds or MSATS as being hazardous air pollutants that required regulation. A subset of six of these MSAT compounds were identified as having the greatest influence on health and included benzene, 1,3-butadiene, formaldehyde, acrolein, acetaldehyde, and diesel particulate matter (DPM). More recently, EPA issued a second MSAT Rule in February 2007 which generally supported the findings in the first rule and provided additional recommendations of compounds having the greatest impact on health. The rule also identified several engine emission certification standards that must be implemented. Unlike the criteria pollutants, toxics do not have National Ambient Air Quality Standards (NAAQS) associated with them which makes evaluation of their impacts more subjective.

The FHWA's ongoing work in air toxics includes a research program to determine and quantify the contribution of mobile sources to air toxic emissions, the establishment of policies for addressing air toxics in environmental reports, and the assessment of scientific literature on health impacts associated with motor vehicle toxic emissions.

Transportation agencies are interested in knowing the air toxics emissions burden associated with mobile sources. This understanding is a primary goal of FHWA's research. Critical components of our work are development and evaluation of methods to analyze and forecast future emissions from facilities and the fleets.

Better understanding of the science underlying MSATs will frame the development of agency policy vis-à-vis air toxics and environmental assessment. In June 2005, FHWA, Nevada Department of Transportation and the Sierra Club entered into a settlement agreement to study the emissions of several air toxic compounds emitted by vehicles in close proximity to roadways. The goal of the study is to assess the contribution of vehicles in the near road environment to air toxic compound concentrations in several US cities. Additional details about the study design, funding and progress may be found on our National Near Road MSAT Study webpage.

This webpage contains documents that have been developed by FHWA for the different topic areas noted above. Future reports, guidance documents and papers will be posted as well as links to useful websites. Associated topics may be found on FHWA's Particulate Matter Webpage.

Related links

To provide Feedback, Suggestions or Comments for this page contact Mike Koontz at michael.koontz@fhwa.dot.gov