In Houston, air pollution concerns usually center on ozone. The area violates federal standards on ozone and perpetually struggles to become compliant.

But Houston environmentalists and businesses are paying increasingly close attention to another pollutant — fine dust. It’s more dangerous than ozone, some say, and the federal government will decide by the end of next year whether the Houston area violates newly tightened federal standards.

“It’s a big uncertainty right now,” said Dan Cohan, an associate professor of environmental engineering at Rice University.

If Houston is found to be in violation of federal standards, it could be costly for local industries, which might need to install new controls to reduce dust. It could also hurt the reputation of a region that has been trying for decades to clean up its air.

The dust, which is also known as fine particulate matter, or PM 2.5, “is probably the deadliest of all air pollutants,” Cohan said. It will “not just affect the respiratory system but actually enter the blood stream, causing cardiovascular effects as well."

The pollutant comes from a variety of sources, including automobile and industrial emissions and plain old dust.

If Houston becomes noncompliant for fine dust, it could become the first area in Texas to do so. The El Paso region also faces this possibility. Its highest fine-dust reading is currently lower than Houston's, but a dusty 2013 could tip the area into noncompliance, said Terry Clawson, a spokesman for the Texas Commission on Environmental Quality.

El Paso already violates federal standards for a coarser type of dust known as PM 10, but scientists say the fine dust is more worrisome.

The federal standard for PM 2.5 was tightened significantly last December as scientists came to appreciate the harmful nature of fine dust. The new standard is 12 micrograms per cubic meter, versus 15 under the old standard.

And a single air-pollution monitor can tip an entire region into “non-attainment” of federal standards.

In Houston, the monitor with the highest readings for fine dust is along Clinton Drive, near the Port of Houston, where truck traffic rumbles by. It shows readings that are slightly above federal standards, 12.1 micrograms per cubic meter on average over the past three years (2010, 2011 and 2012). The Environmental Protection Agency will base its assessment of Houston’s situation on a three-year average.

The EPA is not expected to designate any areas as “non-attainment” until the end of next year — so if 2013 numbers improve, it could bring the three-year average down and pull Houston out of non-attainment.

Should the final numbers show Houston out of compliance, the TCEQ will argue to the EPA that “exceptional dust and smoke events that originated outside of the United States” occurred in 2010 and 2011, and the agency should exclude some of the high measurements, said Clawson, of the TCEQ. Gov. Rick Perry will need to sign off on TCEQ’s recommendation, which is due to the EPA by the end of the year.

Austin Vela, a regional EPA spokesman, said that Texas would need to demonstrate that the events warrant an exception to its rules if the data is to be discounted.

The TCEQ is likely to make a similar argument for El Paso, should a monitor near the Chamizal National Memorial show high readings again this year. Currently, the three-year average for readings at that monitor is 10.7 micrograms per cubic meter, said the TCEQ's Clawson, but a dusty 2013 could push the three-year average above 12 micrograms per cubic meter.

Laura Spanjian, the sustainability director for the city of Houston, said in an email that the numbers for fine particulate matter are “trending slightly downward this year” in the area.

Nonetheless, “the economy is improving, making it imperative that we continue to reduce emissions and implement programs to bring down particulates, particularly in east Houston,” she said.

As Spanjian noted, the numbers at the Clinton Drive monitor have fallen substantially in recent years. Local officials, concerned about staying within federal limits, have worked hard to bring down the figures. Several years ago, for example, officials paved a dusty parking lot nearby. In some recent years Houston's Port Authority has also spent $500,000 annually to spray a coating on roads to reduce dust, according to the port's spring 2013 newsletter.

But environmentalists still have concerns. Adrian Shelley, executive director of Air Alliance Houston, said he welcomed work to reduce fine dust but feared that the monitor near the newly paved parking lot was “unrepresentative of the larger picture of particulate matter in the region.”

Shelley’s group has installed some monitors nearby in an area called Galena Park. While the results have yet to be verified, he said, “our data suggests that particulate matters levels, at least in Galena Park, are several micrograms higher than what the Clinton Drive monitor suggests."

If Houston is declared “non-attainment,” or out of compliance with federal standards, the state would need to craft a plan to reduce fine dust in the region. The EPA would have to approve the plan, which could cover a broad or narrow swathe of the Houston region.

Cohan, of Rice, said that the Houston area already “very stringently” controls emissions of some possible fine-dust pollutants — nitrogen oxide and volatile organic compounds — to reduce ozone levels. Additional compliance measures might bring an increased focus on sulfur-dioxide emissions from power plants, or “gases like ammonia, which have rarely been regulated before.”

Meanwhile, a Houston group could move forward with measures to encourage businesses to help reduce fine dust. On Thursday, the regional air quality planning committee, a group under the Houston-Galveston Area Council of Governments, will vote on whether to recommend to the council’s board that they create a voluntary “advance” plan to battle fine dust.

If the idea goes forward, a plan would probably be created over the next year, said Shelley, a member of the committee.

“We need everybody in the region to participate in the particulate matter advance program now,” he said, “as an aggressive means of achieving reductions before we get that non-attainment designation.”

Editor's note: Adrian Shelley's position with the Houston-Galveston Area Council's regional air-quality planning committee has been corrected to read member, not chairman. In addition, a representative of the council noted that the air-quality planning committee "could" move forward with a plan for voluntary reductions with its vote on Thursday, as opposed to necessarily "hoping to" move forward. The text has been changed to reflect this. In addition, the council of government is the Houston-Galveston Area Council of Governments, not the Houston-Brazoria Council of Governments.