A review of global studies provides strong evidence supporting the Hypothesis of Environmental Inequality. Despite regional study variations, research consistently demonstrates that communities with low socioeconomic status (SES) are disproportionately exposed to higher concentrations of air pollutants, which further exacerbates health disparities in these populations.

Global Evidence for the Hypothesis of Environmental Inequality

In some European studies, higher air pollution concentrations were found among higher SES populations, but the health effects of air pollution were still distributed disproportionately among individuals with a lower SES.  
Several studies found non-linear patterns of inequality. Similarly, a European-wide analysis found non-linear trends where middle-income populations lower exposure to PM10 concentrations when compared to higher and lower-income groups. 



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University of Illinois at Urbana-Champaign

Method Used to Test the Hypothesis:

The method used to test the hypothesis was to review empirical data from previous studies conducted over the past ten years and to include research from around the globe to provide a generalized global perspective. The study only focused on SES and not demographic info.  The study used 37 studies, 22 from North America, 10 from Europe, and 5 from New Zealand, Asia, and Africa.

Methods for Testing the Hypothesis 

Hajat, A., Hsia, C., & O'Neill, M. S. (2015). Socioeconomic Disparities and Air Pollution Exposure: a Global Review. Current environmental health reports, 2(4), 440–450. https://doi.org/10.1007/s40572-015-0069-5


Socioeconomic Disparities and Air Pollution Exposure: A Global Review


Results of European Studies

In North America, the studies primarily found that lower SES individuals and communities were exposed to higher concentrations of air pollution. In the US, evidence supports that many communities with low SES are disproportionately affected by air pollution. For these communities, it is plausible that differential exposure to air pollution may be a contributor to higher associations between air pollution and health than seen in better-off populations. 



Results of North American Studies

The Asian study showed evidence that individuals and communities with lower SES were exposed to higher concentrations of air pollution.


Asia:

A study from Hong Kong explored a municipality with a strong social safety net that had a direct bearing on air pollution inequalities. Among those living in private housing, the lower SES population had higher exposure to PM10 compared to the high SES population.  However, in public housing, no such disparity was found. Similar results were found for several other air pollutants.


Results of Asian Studies

Africa: A long study from Ghana found community SES was inversely associated with both PM2.5 and PM10. In this study higher percentages of both particle matters were found in the lowest SES communities when compared to higher SES communities. Data was also gathered using mobile and stationary measurements in neighborhoods due to the lack of some government data.

Results of African Study

The New Zealand studies  showed evidence that individuals and communities with lower SES were exposed to higher concentrations of air pollution.

New Zealand: The three studies from New Zealand found that low-income and high deprivation neighborhoods had higher concentrations of PM10 compared to higher SES areas.



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