ST. PAUL  — The Minnesota Pollution Control Agency has issued an air pollution health alert for western Minnesota effective through noon today.

The agency said a strong temperature inversion, snow melt and fog are trapping fine-particle pollution near the surface, causing unhealthy levels for sensitive groups.

An air pollution health advisory was issued for the southern half of Minnesota — including the Twin Cities and Rochester — beginning Thursday evening and extending into this morning. Fine-particle concentrations are expected to increase and may reach unhealthy levels for sensitive groups for short periods.

Sensitive groups include the elderly, children, people with cardiovascular or respiratory diseases, and people engaged in strenuous activity indoors or outdoors.

Air quality is expected to improve Friday as a cold front moves across Minnesota.