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In Particulate Matter, the Particulars Matter

Estimated Relative Risk of CVD hospitalization for a .5 microgram per cubic meter increase in the amount of ambient elemental carbon. Risk tends to be higher in the eastern United States, and has a definite spatial pattern. (Click for larger image)

When statisticians start talking about PM, they aren’t referring to political leadership. PM stands for particulate matter, and it’s important because it has a direct effect on the health and well-being of anyone who breathes.

Statistician Montserrat Fuentes has built a career on looking at the effects of PM 2.5 (the 2.5 means that the particles measure less than 2.5 micrometers) on human health, and her work has helped environmental agencies develop their clean air policies. She, her colleague Brian Reich, and their graduate students at NC State are now looking at whether PM should be regulated merely by size, or by composition, and they’re doing it with statistical modeling.

Laura Boehm is interested in the correlation between the chemicals in particulate matter and their effect on respiratory and cardiovascular health. To do this, she’s created a model that measures PM 2.5 levels in the atmosphere at different locations across the country, takes into account the composition of the particulate matter in those locations, and references it against hospitalizations for cardiovascular conditions to see if there are correlations between types and amounts of PM 2.5 across the country. According to Boehm, the immense variation in PM composition across the country means that it’s vital to characterize the health effects of the component chemicals of the PM, not just the size.  “So far, our model has successfully replicated previous findings about the impact of elemental carbon on cardiovascular disease,” she says. “So now we’re going to do similar modeling for all 22 of the major components of PM.” If Boehm’s work is successful, air-quality reporting and standards of the future will focus on the specific pollutant sources most relevant to human health.

Katarina Sucic and Elizabeth Mannshardt are looking at both indoor and outdoor sources of air pollution, to see if indoor sources – which are not regulated – should be subject to the same controls as outdoor pollution.  They combined data from outdoor EPA monitoring stations as well as from indoor monitoring studies to see if exposure to indoor sources of pollution would have a significant impact on respiratory health.  Thus far, their findings indicate that while exposure to pollution increases the risk of respiratory problems by about 2 percent, there isn’t a measurable difference between risks associated with indoor pollution versus outdoor pollution. Including both sources in air quality reporting, however, allows for a more accurate quantification of risk.

For Fuentes, studying these tiny particles leads to a much larger goal: “At the end of the day, these studies are going to give us a much better assessment of what we have in terms of pollution, and enable us to develop air-quality models that will inform and protect the public.”