ST. PAUL, Minn. (AP)— The Minnesota Pollution Control Agency has issued an air pollution health alert for western Minnesota effective through noon on Friday.

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

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

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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.

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