23
Fri, Feb

Regulating particulate pollution

Typography

An MIT analysis of how best to reduce fine particulate matter in the atmosphere has brought some surprising results. Due to past regulations, levels of key emissions that form those harmful particles are now lower than they were a decade ago, causing some experts to suggest that cutting them further might have little effect. Not true, concludes the MIT study. Using an atmospheric model, the researchers found that new policies to restrict the same emissions would be even more effective now than they were in the past. Further analysis elucidated the chemical processes — some unexpected — that explain their findings. Their results demonstrate the importance of tailoring air pollution policies to specific situations and of addressing a variety of emissions in a coordinated way.

An MIT analysis of how best to reduce fine particulate matter in the atmosphere has brought some surprising results. Due to past regulations, levels of key emissions that form those harmful particles are now lower than they were a decade ago, causing some experts to suggest that cutting them further might have little effect. Not true, concludes the MIT study. Using an atmospheric model, the researchers found that new policies to restrict the same emissions would be even more effective now than they were in the past. Further analysis elucidated the chemical processes — some unexpected — that explain their findings. Their results demonstrate the importance of tailoring air pollution policies to specific situations and of addressing a variety of emissions in a coordinated way.

One of the most pervasive and worrisome of today’s air pollutants is particulate matter known as PM2.5. Less than 2.5 microns in diameter, these tiny particles are too small to see, but they can lodge deep within the lungs, causing health problems — including asthma and heart disease — and even premature death. Many of these particles are the result of chemical reactions within water droplets among three types of emissions: nitrogen oxides — known collectively as NOx — primarily from vehicles; sulfur dioxide (SO2) from power plants and industrial facilities; and ammonia (NH3) from agricultural activities. The mix of multiple emissions and the chemistry involved make regulating this type of pollution tricky: Reducing a given emission by 5 percent won’t necessarily reduce PM2.5 formation by 5 percent. Nevertheless, past regulations limiting NOx and SO2 emissions — along with economic trends and increased use of natural gas — have reduced PM2.5 concentrations over the past decade or so.

Even so, problems persist in some regions, so more policy action is needed if damage to human health is to be reduced. But how best to achieve further cuts in PM2.5 hasn’t been clear, according to Noelle Selin, the Esther and Harold E. Edgerton Career Development Associate Professor in MIT’s Institute for Data, Systems, and Society and the Department of Earth, Atmospheric and Planetary Sciences (EAPS). The reason? Background concentrations of NOx and SO2 are now far lower than they were, and that change could profoundly affect the chemistry by which emissions form PM2.5.

As a result, some experts have suggested that further cuts in NOx and SO2 could have diminishing returns. Indeed, several years ago, Selin and her EAPS colleague Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science, wondered whether the dramatic changes in NOx and SO2 concentrations in the last decade had changed the background chemistry such that decreasing SO2 emissions might actually now increase formation of PM2.5 because of how the emitted chemicals interact as they form particles.

Clearly, making sound regulations for particulate pollution is now more difficult than ever. “For policymaking, we’d like to know what the effectiveness of cutting one unit of a given emission would be,” says Selin. “But for every unit of NOx emitted, you might get a different amount of PM2.5 forming depending on background conditions.” Understanding the chemistry of PM2.5 formation is thus critical to designing policies that will “give us the most bang for our buck,” notes Selin.

Continue reading at MIT News. 

Image Credit: iStockphoto/Daniel Stein