Houston Researcher Focuses on Particulate Matter

Cloaked in the clouds of emissions and exhaust that hang over the city are clues that lead back to the polluting culprits, and a research team led by the University of Houston is hot on their trails.

Investigator Shankar Chellam is heading up the case, which hinges on unique identifiers found in fine particulate matter, a mixture of organic, inorganic, or metal material. This material is given off by natural sources, such as sea spray and grassfires, and manmade sources, such as vehicles and industrial operations, and then suspended in the air. "Fine particulate matter is tiny -- about 30 times smaller in diameter than a human hair -- but it carries in it a lot of information about where it came from," explains Chellam, a civil and environmental engineering professor at UH's Cullen College of Engineering. Like any good detective, Chellam has enlisted a team with varying expertise, including urban air quality expert Matthew Fraser of Arizona State University, UH doctoral students of engineering and a NASA scientist.

When their investigation started six years ago, Chellam says, the team was surprised, "maybe naively," that most research at the time focused on ozone, which is formed when emissions mix with sunlight. Much less attention was paid to airborne particulate matter in the Houston area.

Chellam says identifying pollution sources -- even if only by industry or machine type, rather than individual factory or operator -- is a public safety issue, because fine particulate matter is easily absorbed by the lungs and enters the bloodstream. Scientists are only beginning to understand the biochemical basis of how airborne fine and coarse particulate matter and its individual components affect human health, he says.

"Studies show that people living close to highways and refineries are more likely to become seriously ill," says Chellam. "The point of our work is not to specifically identify the individual polluting refineries, necessarily, but to estimate the overall impacts of `catalytic cracking' operations on local particulate matter levels. Also, maybe our findings will one day help toxicologists and epidemiologists determine the risk posed by these metallic elements found in the fine and coarse particles toward humans."

Chemists long have used the process known as "cracking" to break the carbon-carbon bonds in complex organic molecules (such as heavy hydrocarbons) into simpler molecules (such as light hydrocarbons.) Today, most refineries introduce catalysts, usually enriched in rare earth elements, during the cracking process to more efficiently produce gasoline with higher octane ratings.

While industrial pollution sources and vehicles are equipped with filters to reduce emissions during normal operations, those filters are not perfect, Chellam says, and they aren't of any use when episodic, or accidental, emissions occur at refineries.

Fraser said the team's goal is to advance the understanding of the science of air pollution so that more effective and efficient environmental regulations can be written. That's why the team, with funding from the Texas Air Research Center and the Environmental Protection Agency and assistance from engineers from the Texas Commission on Environmental Quality and Bureau of Air Quality Houston, began investigating what Chellam calls "refinery dust," which is created by both planned and unplanned emissions. The heavier dust particles emitted settle around refineries; whereas the fine particles are transported over longer distances.

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