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. Author manuscript; available in PMC: 2021 Jul 1.
Published in final edited form as: Hypertension. 2020 Jun 1;76(1):44–50. doi: 10.1161/HYPERTENSIONAHA.119.14456

Table 1:

Criteria for Categorizing Study Air Pollution Levels

PM2.5 Exposure PM2.5 Range
Low <10 μg/m3
High 10–35 μg/m3
Extreme > 35 μg/m3
Indeterminant Not Reported

For each study, air pollution levels were categorized as “low”, “high”, “extreme,” or “indeterminate” based on participants’ baseline PM2.5 exposure levels. The WHO air quality guidelines were used to define PM2.5 range levels for each category, as shown above. Studies that did not report PM2.5 levels but instead reported other measures of air pollution such as particle number concentration (PNC) were classified as indeterminant.