Risk assessment is the process the U.S. EPA uses to determine if and to what extent the public is at risk from toxic air pollutants.

The risk assessment process has four parts:

• Hazard Identification – What health problems are caused by the pollutant?
• Dose-Response Assessment – What are the health problems at different exposures?
• Exposure Assessment – How much of the pollutant do people inhale during a specific period of time? How many people are exposed?
• Risk Characterization – What is the extra risk of health problems in the exposed population? This part integrates the information from the previous steps to determine the likelihood of risk.

Air Toxics Risk Assessment Reference Library
The U. S. EPA is currently developing an air toxics risk assessment (ATRA) reference library for conducting air toxics analyses at the facility-scale and community-scale. The resulting three volume library will provide information on the fundamental principles of risk-based assessment for air toxics, application of those principles in different settings, and strategies for reducing risk at the local level. Two volumes are complete and the third is expected by the end of 2005.​​​​