New information shows that it may be more challenging than expected to meet tough new air pollution standards that the federal government is proposing .
It's the latest twist in the run-up to new federal rules on ozone, which the U.S. Environmental Protection Agency is expected to announce at the end of October.
Regulators at the Texas Commission on Environmental Quality, who are in charge of writing the ozone-control plan, questioned some of the results, but agreed with parts of it.
Currently, cities are deemed to violate the Clean Air Act if they have more than 85 parts per billion of ozone in their air. Dallas and Fort Worth and nine surrounding counties have violated that standard for years, despite a series of regional plans to reduce the amount of ozone.
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The EPA has announced that it will lower the standard even further, to between 60 and 70 parts per billion.
Researchers at the University of Texas analyzed data from satellites to measure the amount of nitrogen oxides in the air for a month in 2006, then compared those measurements to TCEQ models. The satellite measurements showed as much as 20 percent more nitrogen oxides (or NOX) in the air than the agency's model predicted for the same time period.
That's important because nitrogen oxides are a precursor to ozone. When enough nitrogen oxides are in the air on hot days, they combine with another family of chemicals, known as volatile organic compounds, to form ozone.
David Allen, a UT chemical engineering professor who led the research, cautioned that the satellite images are only a snapshot.
He said the increase could come from several sources - oil and gas drilling in the Barnett Shale, vehicles or even fires.
"What we can see is different rates of progress in different areas. We had huge NOX reductions in the Houston area; Dallas didn't decrease as fast as Houston did," Allen said.
Some officials and clean-air advocates who discussed the findings last week said that the research adds to evidence that gas drilling in the Barnett Shale is contributing to local air pollution levels.
"When you go outside and measure, the levels of NOx are going down everywhere. The exception is Tarrant County, particularly the western area," said Al Armendariz, the regional administrator for the U.S. Environmental Protection Agency in Dallas.
TCEQ spokeswoman Andrea Morrow said Allen's data don't prove that drilling is responsible for the higher NOX levels.
"It is very difficult to associate satellite-based measurements of pollutant concentrations with specific emission sources," Morrow wrote in response to e-mailed questions. "Dr. Allen's data lacked the spatial resolution necessary to distinguish Barnett Shale sources from nearby urban sources, and did not account for some known sources of nitrogen oxides (NOX) including high-altitude aircraft emissions, NOX caused by stratospheric lightning, and NOX transported from distant regions."
At the same time, the TCEQ is conducting an inventory of drilling-related sources of pollution, to get a better idea of the emissions produced in the Barnett Shale. And, Morrow wrote. "Dr. Allen (University of Texas) will be partnering with us in the coming years on additional research being carried out through the Air Quality Research Program grant."
Researchers also found that the TCEQ may have overestimated the amount of ozone reduction coming from cars. In 2003, more than 6 percent of cars and trucks on the road were less than 18 months old. These days, it's closer to 3 percent, the researchers found. That's not surprising, since the economic downturn means fewer people are buying new cars.
That could mean that the amount of ozone-forming pollution from cars and trucks is 10 percent higher than the TCEQ has estimated.
"The real message here is that our emission reduction plans may need to be adjusted as we go along, because assumptions that we make for the future may or may not be accurate," Allen said, referring to new car sales.
Morrow, at the TCEQ, said the agency is using the latest vehicle sales data as it draws up new ozone-reduction plans.
The amount of ozone and ozone-forming chemicals that drift into the Dallas-Fort Worth region from other areas has decreased, but will remain a concern under the new, tighter ozone standard. In 2002, pollution drifting into North Texas from the Houston-Galveston area was responsible for 20 parts per billion of the North Texas ozone levels on peak days. By 2006, Houston was contributing 10 parts per billion on peak days. That's still a significant amount, since the new standard will be between 60 and 70 parts per billion.
The TCEQ concurred.
"We anticipate that local emission reductions as well as transported air pollution will have to be fully evaluated and all possible means of reducing emissions of ozone precursors must be considered," Morrow wrote.
Allen said it's going to be important to invest in research before drawing up the regional ozone plan.
In Houston, local officials lowered the cost of reducing pollution by $2 billion a year by changing their approach to reducing ozone.
Instead of concentrating on reducing the amount of NOx -- the state's historical approach -- local officials concentrated on reducing the amount of specific types of volatile organic chemicals that are highly reactive and create more ozone when they're released. That amounted to fixing leaks, which was much simpler and cheaper than making dramatic reductions in smokestack pollution, Allen said.
Mike Lee, 817-390-7539