CU-led discovery helps clear the air in Houston

Clearing skies over Houston. Photo courtesy of the U.S. Department of Energy


A thick blanket of yellow haze hovering over Houston is a bit thinner thanks in part to research done by scientists at the University of Colorado’s Cooperative Institute for Environmental Sciences.

“Houston has shown small but steady improvements in ozone levels since 2000,” said CIRES scientist Rebecca Washenfelder, one of the researchers who measured levels of air pollutants over the city in 2006.

As well as being home to more than five million people, Houston is base to the largest group of petrochemical factories in the United States. Every day these factories pump toxic fumes into the atmosphere to form ozone—the major culprit of air pollution.

Ozone is a form of air pollution that can damage the respiratory system. In areas with high ozone levels, rubber bands and bike tires get brittle and crack, Washenfelder said. “Ozone is attacking the rubber,” she said. “It’s also attacking your lungs.”

To address the issue, the Texas Commission on Environmental Quality (TCEQ) planned to place stringent controls on the emissions of nitrogen oxides—one of the key ingredients needed to make ozone.

But a study by CIRES and NOAA scientists in 2000 showed that nitrogen oxides weren’t the only culprits in producing ozone. When the crew flew the NOAA WP-3D research aircraft through plumes billowing from the factories below, they discovered another class of compounds—volatile organic compounds (VOCs)— was important for Houston’s high ozone levels.

“This was a big surprise—VOC concentrations were much higher in Houston than in any other U.S. city we’d studied,” Washenfelder said. “It turns out that the petrochemical industries in Houston are big emitters.”

The results inspired TCEQ to regulate VOC emissions from the

petrochemical industry, and when the scientists measured the levels of both nitrogen oxides and VOCs in 2006, the news was good.

“When we returned in 2006, we saw that nitrogen oxide and VOC emissions from many of the industrial complexes near Houston had decreased,” Washenfelder said. “It was great to see that there had been a measurable change.”

Washenfelder believes stricter emissions regulations on combustion sources have led to the decrease in nitrogen oxides. It is less clear, however, whether the reduction in VOCs was due to the new regulations or due to economic changes, she said.

Although whether the entirety of the lower emissions can be attributed to the scientists’ discovery is still unclear, the fact that their earlier study had helped and will continue to help reduce VOC emissions is not.

“There are good indications that air quality has improved as a result of our work,” Washenfelder said. “That’s about as exciting as it gets.”

This originally appeared in Spheres, a journal produced by CIRES.

September 2011

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