ROCHESTER, N.Y. — Wednesday is another hazy day in the Rochester area with moderate air quality, according to the IQ Air index, because of the wildfires burning in Canada. But some parts of the country, including Wisconsin and Michigan, have much worse air quality. Why is that?

First Alert Meteorologist Nate Morris explains how the air quality index works and how pollutants travel thousands of miles away. As the smoke rises, the jet stream carries it from Canada to the U.S. However, because the pollutants are trapped in the upper level of the atmosphere, the air quality near the ground won’t get too bad unless vertical mixing brings pollutants down. Vertical mixing can be caused by fronts, daytime heating, or any kind of turbulence that brings the smoke down.

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In Rochester, there isn’t enough mixing to bring the pollutants down. By Thursday night, the air quality should be back to normal. However, even a moderate status can impact young children, older people, and people with health issues.

Watch News10NBC for the latest on the air quality. We spoke with a doctor at the University of Rochester Medical Center who said even healthy people should be cautious with moderate air quality.

“The air pollution from wildfires is one of the worst exposures that exists. Unfortunately, air pollution affects all of us. Even with normal lungs, it puts some degree of inflammation in the lungs, and it’s something that we’d like to try to avoid,” said Dr. Daniel Croft, associate professor in pulmonary and critical care.

Dr. Croft recommends avoiding strenuous outdoor activity when the air quality is bad and wearing an N95-grade mask if you’re sensitive to pollution.