ALLENTOWN, Pa. — Air quality across the Lehigh Valley deteriorated sharply Sunday, as levels of fine particulate pollution climbed into the “unhealthy” range, prompting regional air quality alerts and raising health concerns for residents.

According to data from IQAir and AirNow, Allentown recorded a U.S. Air Quality Index (AQI)reading of 156 Sunday afternoon — a level classified as unhealthy for all residents. The primary pollutant was PM2.5, or fine particulate matter.

Elevated PM2.5 levels were reported across much of eastern Pennsylvania, including areas between Philadelphia and the Lehigh Valley.

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What is PM2.5?

PM2.5 is airborne particles 2.5 micrometers or smaller, small enough to bypass the body’s natural defenses and penetrate deep into the lungs. These particles can also enter the bloodstream.

Short-term exposure is linked to worsened asthma symptoms, respiratory irritation, headaches and increased risk of heart and lung stress. Children, older adults, pregnant people and individuals with heart or lung conditions are especially vulnerable.

At AQI levels above 150, even healthy individuals may experience symptoms during prolonged outdoor activity.

The weather conditions

Environmental conditions Sunday were favorable for PM2.5 accumulation. Snow removal equipment and residential heating emissions are primary factors.

While snowfall itself does not create particulate pollution, winter storms often increase combustion from heating and snow-clearing equipment while simultaneously trapping pollutants near the ground.

air quality in allentown pa sunday january 18 2026
A screenshot from the r/LehighValley subreddit shows the severity of air pollution early Sunday, Jan. 18. (Photo Courtesy: u/jaxxster7 / Reddit)

Sunday’s AQI reading of 156 marked the highest level recorded in Allentown during the event, with PM2.5 concentrations peaking around 62.5. Levels fluctuated throughout the day, remaining elevated for several hours.

What’s next?

Forecasts indicate air quality may remain compromised into the early part of the coming week. Health officials recommend limiting prolonged outdoor activity while PM2.5 levels remain elevated, particularly for sensitive groups.

Residents are encouraged to monitor local conditions through AirNow.gov.