Houston blows poor air not just hot air

Apr 14 2004

Renyi Zhang, associate professor of atmospheric sciences, modeled Houston's air during the summer months. He found that at night, the city's ozone level (rated in PPBs, or parts per billion) was near zero, but during the day it zoomed to more than 200 PPBs, far higher than the U.S. standard of 120.

Zhang's findings are reported in the current issue of the Proceedings of the National Academy of Science.

The reason for the high daytime rating, Zhang says, can be directly traced to the huge refineries and petrochemical complexes in the area, plus the large amount of auto exhaust in Harris County. The highest ozone levels were found around the city's southeastern edge – near the huge petrochemical plants.

"These plants emit large amounts of highly reactive volatile organic compounds and nitric oxides," Zhang says. "At midday, the ozone readings are very high because of the industrial emissions, coupled with auto exhaust. It creates very big problems for Houston's air, and ozone levels are far above acceptable federal standards. At night, however, the ozone readings register almost zero, forming an urban scale ozone hole which is caused by nitrogen oxide emissions from the refineries and petrochemical plants and power plants. Nitrogen oxides eat up ozone at night.

"It all means a significant health risk is possible for people in this area unless something is done."

Some studies have previously shown Houston to have some of the worst air pollution in the United States. The city also has one of the worst ozone levels in the country, probably due to it size (No.4 in U.S. population) and the fact that 50 percent of the nation's petroleum refining capability is within the city limits.

High ozone levels can be harmful to plants, animals and humans. During the daytime, sunlight catalyzes ozone formation from volatile organic compounds and nitrogen oxides emitted from cars.

Zhang's study, which was funded by the Texas Air Research Center and NASA, shows the city must take steps to curb its air pollution problems.

"There are around 5 million people in the greater Houston area, and many of these people could have health problems associated with breathing bad air, such as emphysema and asthma," Zhang explains.

"We were surprised by these ozone levels, from near zero to far above acceptable. It shows that Houston needs to find a way to curb its emissions. What is needed are alternative energy sources and more efficient means of transportation. If these high readings continue, it poses all sorts of potential health problems for people and the ecological systems in the area."