About the 1999 Assessment
EPA's 1999 national-scale assessment characterizes risks from air toxics at a particular point in time (i.e., 1999). It looks at human health impacts from outdoor, inhalation, chronic exposures and is based on 1999 emissions rates, assuming they remain constant throughout one's lifetime (not today's levels or projected levels). See more information on limitations of the assessment.
The 1999 National-Scale Air Toxics Assessment is based on 1999 emissions data from the 1999 National Emissions Inventory for hazardous air pollutants. It produces results that are useful in identifying potential patterns in emissions, concentrations and risk from air toxics nationwide. It is intended as a prioritization tool for further investigation of specific air toxics and sources. The 1999 assessment includes emissions, ambient concentration estimates, and exposure estimates for 177 of the Clean Air Act's list of 187 air toxics plus diesel particulate matter (diesel PM). For 133 of these air toxics (those with health data based on chronic exposure) the assessment includes cancer and/or noncancer health effects including noncancer health effects for diesel PM.
The 1999 assessment is an updated technical analysis -- EPA released the first such assessment in 2002 which focused on the year 1996 (for emissions, ambient concentration, exposure and risk estimates) and included a smaller subset of pollutants. EPA expects to release a new assessment every three years.