The beautiful weather and lower temperatures brought people back outside in the Triangle Friday, but air quality experts caution that a clear day may not be all that it appears.

During Thursday's smoky haze, a meteorologist with the state division of Air Quality said Raleigh's air quality index reached a "Code Purple" because of the high volume of particles in the air.

"We measure the air quality in micrograms of particulates per cubic meter," said meteorologist Nick Witcraft. "Thirty-five micrograms is Code Orange, 65 is Code Red. But yesterday in downtown Raleigh, we measured 200 micrograms for about a five-hour period."

Asthma sufferer Katie Dunn was relieved to have better air to breathe. She wore a mask for most of Thursday at her job at the Department of Transportation. Dunn said she checks the air quality index every day, summer and winter.

"If I see that it's red or orange, then I make sure that I have extra water," she said. "So I don't get congested."

Dr. Monica Kraft of Duke University Medical Center said that people with lung problems suffer the most. And while medicine may help with the irritation and inflammation they experience, it doesn't remove the particles from their lungs.

"Some of them are inhaled back out, others are cleared by cells in our lungs and eventually cleared," Kraft said. "So the medicines can help, sort of as an intermediate if you will, while this process is going on."

Most people's lungs work pretty efficiently. Still, Kraft says it's a good idea to stay alert to air quality reports and try not to overexert yourself outside when the index is high. But don't depend on your eyes or even your nose to tell you that.

"You can be fooled a little bit by walking out side and looking in your front yard," she said. "I think you should get more quantitative information before you make a decision on your activities for the day."

NBC 17 updates weather information and air quality advisories on its weather page.

The N.C. Department of Environment and Natural Resources' Division of Air Quality provides daily air quality forecasts and even offers an e-mail alert system.