Relatively warm, moist weather conditions led the Minnesota Pollution Control Agency Thursday to post an air pollution health advisory for the southern half of Minnesota running through early Sunday morning.

An advisory means conditions are approaching unhealthy levels for sensitive groups. It is one step short of an alert.

The moist air is trapping pollution close to the ground, which is elevating levels of fine particle pollution, said Rebecca Place, MPCA's air quality index coordinator.

"It's caused by vehicle exhaust or burning wood. They're very small particulates in the air and they can get into your lungs and cause respiratory problems," she said.

People with heart disease and lung disease may experience worsening health problems during an air pollution advisory.

If the MPCA upgrades its advisory to an alert, the list of sensitive populations will expand to include young children and elderly adults.