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EPA Findings Improve Air Quality Modeling Nationwide

EPA-funded scientists make major air pollution discovery, improving models used to protect human health.

Map of the US showing the Air Quality Index

New EPA-funded research has improved air quality modeling which will ultimately improve air quality and reduce related health effects.

A major fraction of harmful particles in air is made of a complex mixture of organic material. Until recently, models that predicted the amount of organic aerosols in the atmosphere were off the mark by orders of magnitude—and nobody knew why.

EPA-funded scientists helped discover that aerosols actually come from two different places. Some are directly emitted from primary sources like traffic exhaust, while others are generated by transformations that occur once pollutants spend time in the atmosphere (secondary sources).

This dual-source revelation was a major breakthrough, but scientists still needed to understand the relative contribution of each source to the total amount of aerosols in the atmosphere.

Dr. Sherri Hunt, an EPA atmospheric scientist and project officer for modeling research, explained why this was such a critical question to answer.

“If states really want to control air pollution, they need to know where the harmful particles are coming from. Without this information, they can’t adequately protect people,” she said.

In a 2007 paper1 published in Science, EPA grantees showed that secondary sources are actually a much more dominant contributor to total organic aerosol than primary sources.

According to Allen Robinson, a Carnegie Mellon professor and EPA grantee, the study revealed that scientists had been overlooking a whole subset of emissions.

 “One of our key findings was that this secondary transformation leads to more particulate matter in the air,” he said.  “We may have been underestimating how sources such as cars and trucks contribute to pollution."

It was previously thought that urban residents are mainly exposed to emissions from direct sources like traffic exhaust. The EPA research showed otherwise—that the majority of people are actually exposed to emissions in the atmosphere that have transformed over time. Since secondary emissions may be more toxic, this is a vital piece of information.  

In 2009, grantees pushed further with a Science paper2 that presented a new model framework. The new model captures dynamic aging behavior of particles in the atmosphere, producing a more accurate picture of real-world atmospheres.

Though further research is needed to understand and incorporate the nuances of atmospheric transformation, the new model is already making an impact.

Researchers have incorporated it into the Community Multi-scale Air Quality system (CMAQ), a “super model” that is used by regulators at the federal, state and local levels. CMAQ helps decision makers predict air quality and determine how to control pollution. With the inclusion of the new findings, CMAQ can now more accurately model air pollution particles.

“The more we uncover through research,” Dr. Hunt said, “the better models will become.”

As the science progresses, so will the ability of regulators to protect people.

1 Allen L. Robinson, et al, 2007. Rethinking Organic Aerosols: Semivolatile Emissions and Photochemical Aging. Science 315, 1259 Exit EPA Disclaimer

2 J. L. Jimenez, et al, 2009. Evolution of Organic Aerosols in the Atmosphere. Science, 326,1525. Exit EPA Disclaimer

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