Knoxville — Knoxville and much of East Tennessee is under an orange air quality alert.
The alert means that people with sensitive respiratory issues may have difficulty breathing during outdoor activities.
In East Tennessee, three main factors contribute to air quality issues: topography, weather and pollution.
The Environmental Protection Agency says that sunshine makes pollution undergo chemical reactions that produce smog. High temperatures speed up those reactions in the air.
TVA says that in the region it serves, two-thirds of emissions that contribute to air pollution come from vehicles, boats and planes.
"I-75 / I-40 runs right through the Tennessee Valley, so you've got thousands of cars moving along that roadway every single day, and that's adding pollution to a valley which is not being flushed out because we do not have any wind right now," WBIR Meteorologist Cassie Nall said.
Other major contributors to poor air quality are power plants and factories.
For its part, TVA has taken considerable steps to reduce emissions.
In addition to less reliance on coal, the authority has installed scrubbers at its facilities to change the chemical nature of its emissions.
"We always have cars, so just because we have light winds and sunshine and warm temperatures, that doesn't necessarily mean we'll have poor air quality," Nall said. "All the pieces of the puzzle have to come together just right and unfortunately they are right now."