Southerly winds blowing warm air and pollutants into Minnesota on Tuesday caused the Minnesota Pollution Control Agency to issue an air quality alert for the southern half of the state.

Air quality is expected to improve Wednesday as a cool front moves into the state and temperatures are forecast to fall into the upper 60s, the Weather Service said.

Ground-level ozone was expected to reach high levels between noon and 8 p.m. Tuesday when the alert — including the Twin Cities area, St. Cloud, Hinckley, Rochester, Mankato, Marshall and the tribal nations of Mille Lacs, Upper Sioux and Prairie Island — will be in effect.

The bad air will push MPCA's air quality index into the unhealthy Orange level, the third-highest on the six-level scale.

Children, seniors, people with lung and heart diseases and those playing sports or working outdoors are advised to take it easy and avoid prolonged outdoor activity until air quality improves, the MPCA said.

Ozone is produced on hot, sunny days by a chemical reaction between volatile organic compounds and oxides of nitrogen. High levels can aggravate lung diseases such as asthma, emphysema and COPD, the MPCA said.

Symptoms can include difficulty breathing deeply, shortness of breath, throat soreness, wheezing, coughing or unusual fatigue, the MPCA said.

Reducing outdoor burning and use of gas-powered machinery and vehicle trips during the afternoon and early evening when ozone levels are highest can also help reduce air pollution, the National Weather Service said.