As intense heat continues to move across the eastern two-thirds of the nation throughout the week, air quality will likely suffer as a result.
The cities plagued most by the heat will be St. Louis, Kansas City, Chicago, D.C. and Philadelphia.
Air quality will deteriorate in these areas, with most of the East and Midwest facing moderate health concern as a result of the air quality.
According to the air quality index at airnow.gov, a moderate health concern means that 'air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.'
Areas of more serious concern include Atlanta, Pittsburgh, St. Louis, Chicago, Detroit, Cleveland and Cincinnati.
These areas have been temporarily deemed unhealthy for particularly sensitive groups. According to airnow.gov, "Members of sensitive group may experience health effects."
The general public is not likely to be affected, the site explains.
It's not a coincidence that poor air quality usually accompanies heat waves.
"When you get a large area of high pressure promoting widespread heat, you also get a large zone of stagnant air," said AccuWeather.com Meteorologist Meghan Evans.
"Smoke and ozone can be trapped in the atmosphere, leading to poor air quality."
For the full story on the heat, click here.
A taste of spring is coming to Pittsburgh but it will be short-lived as colder air and a possible storm arrives at midweek.
Warmer air will move into Atlanta this weekend and into next week, helping erase the cold start to March.
Showers will return early in the week with milder, drier weather is in store for the weekend.
Temperatures will remain on a roller coaster ride in Boston the next several days.
With below-average temperatures gripping the city for much of the early month, Detroit will see higher temperatures into Tuesday.
Harrisburg will experience a taste of spring before colder air and a possible storm arrives at midweek.
Brinkley, AR (1909)
Tornado killed 49 and caused $600,000 worth of property damage.
Philadelphia, PA (1941)
8.0" of snow.
Philadelphia, PA (1960)
Record low of 14 degrees -- 2nd day of 3 consecutive record lows, and 1 of 4 set during March 1960.