Raleigh, N.C. — An indoor smoking ban has resulted in an 89 percent improvement in air quality in North Carolina restaurants and bars in recent months, public health officials said Friday.

A state law that went into effect on Jan. 2 prohibits smoking at nearly all restaurants and bars. Cigar bars and private clubs are exempt from the law if they meet certain requirements.

“These results show that North Carolinians are already reaping the benefits of our smoke-free air law by breathing healthier air in restaurants and bars,” State Public Health Director Dr. Jeffrey Engel said in a statement. “Secondhand smoke is a very serious health threat. Exposing adults to secondhand smoke causes immediate adverse effects on the heart and blood vessels, increasing the risk of heart disease and, over time, lung cancer.”

Air quality was measured using a machine that measures the number of particles in the air smaller than 2.5 micrograms. The U.S. Environmental Protection Agency measures these particles in outdoor air because they are known to cause breathing problems and contribute to premature deaths.

Burning tobacco releases significant amounts of these particles, officials said.

Officials collected air samples from 152 restaurants and bars in six counties from 2005 to 2007, and the results were compared with samples collected from 78 restaurants and bars in seven counties between January and March.

The restaurants and bars where the samples were collected weren't aware of the action, officials said.

Through April 11, health officials statewide had received only 18 complaints of violations of the indoor smoking ban, officials said.

Businesses that break the no-smoking law can be fined up to $200 per day, and smokers themselves could get burned with a $50 fine if they keep puffing after they're told to stop.