Regulators Must Rethink Strategies For Soot Emission, Researchers Urge

In a March 2 article published in the journal Science, professors Allen L. Robinson and Neil M. Donahue report a new conceptual model for how microscopic particles behave in the atmosphere that raises new questions about current regulations.

The research found new chemical processes that occur after soot and gaseous pollutants are emitted from cars and trucks, changing the chemical and physical properties of the soot particles and creating new particulate matter. These new particles are potentially more toxic and may have a stronger influence on cloud formation that can alter the global climate.

"One of our key findings is that this chemical processing leads to more particulate matter in the air, meaning that regulators are likely underestimating how sources such as cars and trucks contribute to pollution," said Robinson, an associate professor of mechanical engineering and engineering and public policy. "We need to take a holistic approach to regulating these sources that account for all emissions." Accounting for these new processes improves the predictions of the models federal and state governments use to develop regulations.

"A second important finding is that the properties of this new particulate matter are different than we previously thought and potentially more toxic," added Donahue, an associate professor of chemical engineering and chemistry.

Particulate matter poses a serious health problem. Fifty thousand Americans are thought to die prematurely each year due to particle exposure, and almost 70 million Americans live in areas that violate the federal standard. That standard was strengthened in September after scientists, armed with years of studies showing that these particles can damage lungs and the heart, advised the Environmental Protection Agency (EPA) that the previous standard of 65 micrograms per cubic meter of air was too loose.

A third key implication has to do with how the chemical process leads to a spreading of pollution over a larger geographic region. "We're seeing that urban pollution doesn't stay contained in the cities, but impacts rural and other downwind areas, creating even more complicated issues for regulators," Robinson said.

Fine particles such as smoke or dust form droplets in clouds and affect how much sun is able to pass through the cloud to earth, as well as the amount of moisture that is returned to earth. Both clouds and sunlight play key roles in climate change. The effects of particulate matter were identified as key to uncertainty in a recent report by the Intergovernmental Panel on Climate Change (IPPC) summarizing the state scientific knowledge on the impacts of human activities on global climate.

"For the longest time, particulate matter has been the least understood component of the climate system. The more we understand particulate matter, the more we realize that complexity has been masking our ability to calculate how big a role greenhouse gases have played in inducing global warming," said Donahue. "Moreover, the new mechanism we found changes the chemical properties of particles, making them more likely to participate in cloud formation. Therefore, particulate matter may be having a stronger influence on global climate than previously thought."