The Minnesota Pollution Control Agency has extended the air pollution health alert issued for the Twin Cities and Rochester through Tuesday.
The MPCA issues an air pollution health advisory when the amount of fine pollution particles in the air approaches a level that is considered unhealthy for certain groups.
Those groups include people with respiratory or cardiovascular problems, young children, the elderly, and people who participate in activities that require heavy exertion.
The MPCA also issued an air pollution health advisory, a less severe rating, for the same areas on Wednesday.
The southern two-thirds of the state, including Duluth, Detroit Lakes, Brainerd, and Marshall, remains under a air pollution health advisory for today through Wednesday.
MPCA officials say that dense fog last night, combined with calm winds, has caused fine particle concentrations to increase to unhealthy levels. Officials expect the level to fall gradually this afternoon as the fog dissipates.
But calm winds and high relative humidity will continue to trap pollutants, keeping air quality conditions unhealthy for sensitive groups. As the winds move to the east on Tuesday, additional pollutants will travel to the region, prolonging high pollution levels.
The MPCA cautions that even individuals who are otherwise healthy may experience health problems when air pollution increases.
Officials have urged residents to reduce or postpone activities that lead to deep or accelerated breathing, as fine pollution particles can be inhaled deeply into the lungs.
Exposure to high levels of fine particles may cause chest pain, shortness of breath, coughing and fatigue, even after air quality has improved.
Officials have urged residents to help reduce air pollution by carpooling, using public transportation, and avoiding car idling.
During poor air-quality times, the MPCA also recommends that people postpone burning wood and reduce their energy consumption.
Hourly air quality updates are available at the MPCA's Air Quality Index Web site.