Air Pollution Exposure Inequality Persists in Massachusetts.

Despite overall reductions in ambient air pollution in Massachusetts, exposure continues to fall unequally along racial/ethnic, income, and education lines, according to a new study led by a School of Public Health researcher.

The study, published in Environmental Research, found concentrations of nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5) decreased across the state between 2003 and 2010, but exposure remained higher in predominantly Hispanic and non-Hispanic black communities. Within the state’s cities, the researchers found exposure inequality actually increased slightly between racial/ethnic groups during the study period.

“Although ambient air pollution concentrations have decreased across all of Massachusetts, these reductions had a higher relative impact on populations that were already in the lowest exposure categories, hence the increase in exposure inequality,” says Patricia Fabian, research assistant professor of environmental health and the study’s senior author.

While numerous previous studies have shown disparities in air pollution exposure at one point in time, the current study was one of the first to track those disparities over space and time, allowing for a more nuanced picture of exposures as demographics shift in a given area.

Using data from the 2000 and 2010 Census and the 2006–2010 American Community Survey on race/ethnicity, income, educational attainment, and rural/urban land classification, the researchers calculated exposures using modeled PM_2.5 concentrations from 2003 to 2010 and NO₂ concentrations from 2005 to 2010. The researchers then characterized the disparities using the Atkinson Index, a quantitative measure for relative inequality.

The researchers found the average annual PM_2.5 concentrations across the state decreased by 35 percent between 2003 and 2010 and the average annual NO₂ concentrations decreased by 24 percent between 2005 and 2010. However, non-Hispanic black populations continued to have the highest exposures, followed by Hispanic populations. The gap between exposures for non-Hispanic black populations and non-Hispanic white populations remained the same, while the gap between Hispanic and non-Hispanic white populations slightly increased.

The authors noted that exposure to NO₂ was more dramatically unequal than exposure to PM_2.5, perhaps because NO₂ is strongly linked to automobile exhaust, which can vary within a city based on traffic patterns, while PM_2.5 is derived from a wide variety of sources and tends to have more regional concentrations.

“Greater inequalities in urban areas, where there is often substantial segregation, reinforces the importance of targeted exposure reduction strategies within vulnerable populations and neighborhoods,” the authors wrote. By looking at these inequalities over time, the authors said, the study points to the possibility that sociodemographic changes may impact land-use decisions, environmental policy enforcement, and other factors influencing emissions.

More longitudinal, individual-level studies are needed to understand this “complex dynamic,” the authors wrote.

The study was led by doctoral candidate Anna Rosofsky. Other authors were: Jonathan Levy, professor of environmental health; Patricia Janulewicz, assistant professor of community health sciences; and Antonella Zanobetti, principal research scientist in the Department of Public Health at Harvard T.H. Chan School of Public Health.

The study came out of the Center for Research on Social Stressors in Housing Across the Life Course (CRESSH). It was supported by the National Institutes of Health’s National Institutes on Minority Health and Health Disparities and the Environmental Protection Agency.

—Michelle Samuels