The Environmental Protection Agency said a long, hot summer made for poor air quality in parts of North Texas.
It's something residents have seen firsthand.
"On hot summer days, you go out there, working around or doing something in the yard, and you find it's very difficult to breathe," said Jim Skelly, of Plano.
The EPA deems nine counties around Dallas-Fort Worth areas of serious nonattainment for ground-level ozone pollution.
The federal agency says the area has improved its air quality but currently reports an ozone emission value that is still well above the federal standard.
The EPA is considering adding Hood and Wise counties to its nonattainment list because "emissions from a wider area are likely contributing to the problem," spokesman Joseph Hubbard said.
At one Plano inspection site, inspectors say up to one in six older vehicles that require a manual emissions test do not pass.
After several environmental groups call for even tougher standards on the national level, some people in North Texas just want to see the current rules work.
"All along, it's been based on standards being set and standards being enforced," said Ashok Khilnani, of Plano. "Unless that happens, it's difficult to clean up the air."
Opponents have argued that tighter standards are bad for business, specifically industry.