Current air quality policies aimed at reducing harmful effects of PM2.5 – particles in ambient air that are 2.5 microns in diameter or smaller – are driven by an assumption that the relationship between PM2.5 mass and its health effects is globally uniform. A new study led by civil and environmental engineering at Illinois associate professor Vishal Verma highlights the flaws in this assumption by demonstrating how intrinsic toxicity of PM2.5 varies regionally due to differences in chemical composition.
Historically, the epidemiological studies from which policymakers gather information are based on a model that explains PM2.5 toxicity as a linear function of mass. Most of these studies, however, only focus on samples from certain geographic regions, leaving questions as to whether or not applying their conclusions globally results in the most effective efforts to reduce PM2.5 health impacts.
To further investigate the relationship between mass and toxicity, Verma’s group collaborated with researchers from 6 different institutions to collect a large number of PM2.5 samples from 14 different sites across 4 different continents (North and South America, Europe, and Asia). They then evaluated the toxicity of these samples using 5 different metrics.
Their results showed that relationships between mass and toxicity varied among sample sites from different geographic regions. For example, places like India, where mass PM2.5 mass concentrations are high, had much lower intrinsic PM2.5 toxicity than places like the Midwestern United States, with low PM2.5 mass concentrations. Regional differences imply that chemical composition, which drives intrinsic toxicity and is impacted by geographic factors, plays an important role in determining the toxicity of PM2.5 alongside mass.
Consequently, the use of globally generalized models to evaluate health risks results in unrealistic estimations of morbidity and mortality due to PM2.5. This is especially true in places like China and India, where their high PM2.5 mass concentrations would predict much higher levels of PM2.5 health impacts based on the linear models. As a result, policy measures aimed at reducing PM2.5 mass in these areas will not result in significant risk reduction.
To help change this trend, the study emphasizes the need for developing region-specific curves to better consider varying associations between mass and toxicity across the globe. By addressing up front the differences in chemical composition that can impact toxicity, Verma and his team hope to prompt further research towards improving regional understanding of intrinsic PM2.5 toxicity and the effectiveness of air quality policy worldwide.
The full paper, “Inter-continental variability in the relationship of oxidative potential and cytotoxicity with PM2.5 mass,” was published in Nature Communications and was selected as a Nature Communication Editor’s Highlight, an honor bestowed to the 50 best papers recently published in a given field of study.
This research was supported by the National Science Foundation.