Explanation of Hazardous Air Pollutant Ranking Criteria

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Explanation of Hazardous Air Pollutant Rankings

Scorecard ranks states and counties based on the magnitude of cancer and noncancer health risks associated with estimated exposures to 40 hazardous air pollutants. For each of the health risk ranking criteria defined below, you can specify whether you want to rank your state or county based on the hazardous air pollutants emitted from all sources combined, or from specific source categories (area, mobile, or point sources). Source-based rankings do not include the estimated health risks associated with "background" levels of pollutants. Each of the ranking criteria are defined below, with links to more information if you need it.
NOTE: These rankings are based on exposure estimates derived from 1996 emissions data. There are important uncertainties associated with using models to predict current air quality. Scorecard risk estimates are based on EPA exposure estimates and provide a perspective on the magnitude and sources of hazardous air pollution problems. They are not definitive evaluations of health risk in a particular locale.

Average Individual's Added Cancer Risk (per 1,000,000)
The estimated individual risk of getting cancer due to a lifetime exposure to outdoor hazardous air pollutants. Because the Clean Air Act's goal is to reduce lifetime cancer risks from hazardous air pollutants to one in one million, Scorecard expresses added cancer risk in these units: an added risk of 550 per 1,000,000, for example, is 550 times higher than the Clean Air Act goal.
Note that cancer risk estimates are calculations based on models - they are useful for ranking purposes but are not necessarily predictive of any actual individual's risk of getting cancer.

Noncancer Cumulative Hazard Index
A hazard index is the ratio of a hazardous air pollutant concentration divided by its Reference Concentration, or safe exposure level. If the hazard index exceeds one, people are exposed to levels of HAPs that may pose noncancer health risks. The cumulative hazard index is the total hazard index, summing over all HAPs with noncancer effects in an area. Each HAP contributes its single chemical hazard index to the total.
Note that noncancer hazard indices are calculations based on models - they are useful for ranking purposes but are not predictive of any actual individual's risk of getting a specific disease.

Population in Areas Where Cancer Risk Exceeds 1 in 10,000
The number of people living in areas where the added cancer risk associated with outdoor hazardous air pollutant exposures is greater than 1 in 10,000. This number of people are exposed to levels of HAPs that exceed the Clean Air Act's cancer risk goal by a factor of 100.

Population in Areas Where Cancer Risk Exceeds 1 in 1,000
The number of people living in areas where the added cancer risk associated with outdoor hazardous air pollutant exposures is greater than 1 in 1,000. This number of people are exposed to levels of HAPs that exceed the Clean Air Act's cancer risk goal by a factor of 1,000.

Population in Areas Where Hazard Index Exceeds 1
The number of people living in areas where the noncancer cumulative hazardous index is greater than one. This number of people are exposed to levels of HAPs that exceed the Clean Air Act's noncancer risk goal.

Population in Areas Where Hazard Index Exceeds 10
The number of people living in areas where the noncancer cumulative hazardous index is greater than ten. This number of people are exposed to levels of HAPs that exceed the Clean Air Act's noncancer risk goal by a factor of 10.

Population in Areas Where Hazard Index Exceeds 100
The number of people living in areas where the noncancer cumulative hazardous index is greater than one hundred. This number of people are exposed to levels of HAPs that exceed the Clean Air Act's noncancer risk goal by a factor of 100.