Environmental Inequality in Exposures to Airborne Particulate Matter Components in the United States

Background: Growing evidence indicates that toxicity of fine particulate matter ≤ 2.5 μm in diameter (PM(2.5)) differs by chemical component. Exposure to components may differ by population. Objectives: We investigated whether exposures to PM(2.5) components differ by race/ethnicity, age, and socioeconomic status (SES). Methods: Long-term exposures (2000 through 2006) were estimated for 215 U.S. census tracts for PM(2.5) and for 14 PM(2.5) components. Population-weighted exposures were combined to generate overall estimated exposures by race/ethnicity, education, poverty status, employment, age, and earnings. We compared population characteristics for tracts with and without PM(2.5) component monitors. Results: Larger disparities in estimated exposures were observed for components than for PM(2.5) total mass. For race/ethnicity, whites generally had the lowest exposures. Non-Hispanic blacks had higher exposures than did whites for 13 of the 14 components. Hispanics generally had the highest exposures (e.g., 152% higher than whites for chlorine, 94% higher for aluminum). Young persons (0–19 years of age) had levels as high as or higher than other ages for all exposures except sulfate. Persons with lower SES had higher estimated exposures, with some exceptions. For example, a 10% increase in the proportion unemployed was associated with a 20.0% increase in vanadium and an 18.3% increase in elemental carbon. Census tracts with monitors had more non-Hispanic blacks, lower education and earnings, and higher unemployment and poverty than did tracts without monitors. Conclusions: Exposures to PM(2.5) components differed by race/ethnicity, age, and SES. If some components are more toxic than others, certain populations are likely to suffer higher health burdens. Demographics differed between populations covered and not covered by monitors.