For the third time in four years, environmental regulators have cited Celanese Acetate for failing to properly monitor emissions from its sprawling Giles County plant.

The company agreed to pay a fine of $13,122.20 to resolve its most recent citation from the Virginia Department of Environmental Quality.

As with the two previous enforcement actions, state regulators did not allege excessive emissions at the plant, which makes materials used in cigarette filters.

In September, a DEQ evaluation found that the plant failed to properly monitor nitrogen oxide from a large boiler used to generate steam. As a result, emissions data was not collected for at least 22 of 30 days, as required by state regulations.

Although the violation did not involve actual pollution, a local environmental group said it still points to problems at the plant.

"How can a company control its pollution if it isn't sure of what it is pumping into the air 73 percent of the time?" asked Chris Wilson, chairman of the Sierra Club's New River Valley chapter.

"This is a small sign of a much larger problem within an industry that largely goes unregulated ... and when they are punished it is a simple slap on the wrist," Wilson said.

A Celanese spokeswoman said the company is "committed to premier environmental performance."

"We continually look for ways to improve operation and ensure compliance," said Linda Beheler, noting a $250,000 project to improve the plant's monitoring system.

The problems identified by the DEQ have since been corrected, according to a consent order between the agency and Celanese filed earlier this month.

It was the second time in recent years that regulators have found problems with the monitoring of nitrogen oxide emissions from boilers at the plant.

Nitrogen oxide is a source of acid rain and contributes to low-level ozone, an ingredient of smog. It also can cause respiratory problems and complicate cases of childhood asthma.

In 2008, Celanese agreed to pay a $60,000 fine after it was cited by the Environmental Protection Agency for failing to test a device that measures nitrogen oxide emissions. The EPA also found that the company had failed to monitor valves, connectors and heat exchangers.

And in 2010, failure to properly monitor valves in the plant's anhydride manufacturing unit resulted in a $15,715.50 fine from the DEQ.

With factories in the United States, Europe, Mexico and Asia, Celanese Acetate makes products used in filters, film applications and other industrial uses.

Located on the banks of the New River, the Giles County plant employs about 540 people, making it the county's largest employer.