An air quality alert in effect for the Twin Cities and portions of central Minnesota until 6 p.m. Thursday has been expanded to include areas of southern Minnesota.

The Minnesota Pollution Control Agency says fine particle readings are considered unhealthy for sensitive groups because of light winds, clear skies and a strong inversion that led to air pollutants being trapped close to the ground.

On Wednesday, the agency added areas stretching down to the Iowa-Minnesota border including Rochester, Mankato and Albert Lea. The alert also covers a stretch of central Minnesota to the north and west, including Willmar and Hutchinson.

By Thursday afternoon, a front is expected to move into the state and bring in more healthy air.

Among those who could be affected the next couple of days, the MPCA says:

• People with asthma, chronic obstructive pulmonary disease (COPD) and other conditions.

• Those with heart disease or high blood pressure.

• Young children and older adults.

• Athletes, outdoor workers and others doing extended physical activity.

For more, check out the MPCA alerts and conditions online.