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By Amanda Greenwood
Associate News Editor
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Thousands of residents in communities across parts of California and Oregon have been advised to stay inside by the Environmental Protection Agency (EPA) due to elevated amounts of fine particle pollution (PM2.5) in the atmosphere.
As of Thursday, January 15, 2026, at 3.00 a.m. ET, the EPA’s AirNow map showed that the air quality had reached an “unhealthy” level, particularly affecting communities in Lakeview and La Pine in Oregon, and Fresno in California.
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Why It Matters
The EPA considers PM2.5 to be one of the most harmful types of particle pollution.
This is because the particles are so fine, less than 2.5 micrometers in size (smaller than a single strand of hair), that they can be unknowingly inhaled, penetrating deep into the lungs and the bloodstream. This has the potential to trigger or worsen certain health problems, such as asthma or heart and lung conditions, meaning people in sensitive groups, including the elderly, children, and those with existing medical conditions, are vulnerable.
At an “unhealthy” level, PM2.5 can also affect general members of the public, as it can cause mild to severe health symptoms ranging from coughing, eye, nose, and throat irritation to shortness of breath and chest tightness.
The EPA is, therefore, urging people in sensitive groups to avoid all intense or long outdoor activities and advising everyone else to reduce or shorten their outdoor activities, warning that “even if you are healthy, you may experience temporary symptoms from exposure to elevated levels of particles.”
This is because the more time spent outside means more exposure to the polluted air, and strenuous outdoor activities tend to lead to heavier, deeper breathing, which means the tiny particles of pollution are more likely to enter the lungs and bloodstream.
What Causes PM2.5?
Although the EPA hasn’t established the source of high levels of PM2.5 across parts of California and Oregon, PM2.5 can come from a variety of sources, including dust from construction sites and unpaved roads, smoke from wildfires, and emissions from vehicles, or power and industrial plants.
The EPA measures, records, and communicates the level of air quality across America using the Air Quality Index (AQI).
The AQI is a standardized scale ranging from 0 to 500 that categorizes air quality from “good,” which means there are minimal concerns over air pollution, to “hazardous,” signaling a health emergency in which everyone is likely to experience adverse health effects.
Advice From The EPA
Those in affected areas should monitor the AirNow Map and look out for updates from the EPA, as conditions can often rapidly change.
They should also be aware that PM2.5 can sometimes affect the quality of air indoors. For this reason, the EPA advises using indoor air cleaning filters and avoiding using candles, wood-burning stoves, and open fires.
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