Taking a deep breath in Houston could literally be toxic. And that's not just due to the nearby oil refineries.
Researchers have determined that ozone levels in Houston increased by 50 to 100 percent as a result of smoke wafting in from Alaskan and Canadian forest fires, thousands of miles away. The report, based on data from satellites and weather balloons, appears in the Sept. 26 issue of the Journal of Geophysical Research.
Advertisement
In the upper atmosphere, or stratosphere, ozone, O3, forms a protective layer that shields the Earth from the sun's ultraviolet radiation. But in the lower atmosphere, or troposphere, ozone becomes smog, contributing to global warming and threatening human health.
In the summer of 2004, physicist Gary Morris, now at Valparaiso University in Indiana, launched the Tropospheric Ozone Pollution Project. Morris and his team launched weather balloons as high as 5 km above Houston to measure ozone concentrations at varying altitudes. The measurements comprise the first long-term record of vertical ozone distribution—as opposed to ground-level ozone—in any major U.S. city.
"There's been a long record of surface measurements," Morris said, adding that ozone at higher altitudes was rarely measured. "That's where the balloons come in. You get a third dimension, and can distinguish between what's brought in and what's local."
Forest fires in Alaska gave Morris's team an opportunity to assess the air that was moving into the region. Using satellite and spacecraft data from NASA, the researchers tracked an air mass that originated as smoke from the fires. Originating in Alaska on July 12, 2004, the mass moved steadily across the U.S., arriving in the Houston area seven days later.
The data from NASA, plus weather balloon measurements, revealed a 50 to 100 percent increase in Houston's tropospheric ozone on July 19 and 20, 2004—likely due to the arrival of the Alaskan air mass.
"This study points out how interconnected things are," Morris said. "Over the last 15 to 20 years, there has been an increased awareness of the larger global impacts on local phenomena."
Houston is one of the most polluted cities in the U.S. and regularly violates ozone standards issued by the Environmental Protection Agency. According to Morris, Houston's high levels of pollution result from a combination of hot, stagnant weather; a large commuter population; and the city's large petrochemical industry.
In fact, a report released by Rice University on Sept. 27 highlighted the effects that four toxic pollutants—benzene; 1,3-butadiene; formaldehyde; and diesel particulate matter—have on Houston's air quality. (In 2004, Houston's air contained the highest level of 1,3-butadiene of any city in the U.S.—20 times more than the air in Los Angeles. The chemical, a product of petrochemical manufacturing, is present in vehicle exhaust.)
"Based on the results of our study, we strongly recommend immediate action to lower the ambient concentrations of the four hazardous air pollutants we researched," Matt Fraser, the principal investigator and a civil and environmental engineer at Rice, said in a press release. "The level of air toxics concentration that we're seeing in the Houston area poses a dangerously high risk of cancer and other health problems."