Air quality advisory issued in US due to hazardous smoke pollution from Canadian wildfires

Several states have issued Code Orange, Code Red and Code Purple air quality warnings as elevated levels of fine particulate matter (PM2.5) push air pollution into unhealthy and, in some places, dangerous areas, according to advisories compiled by the National Weather Service (NWS).

From New York and Pennsylvania to Michigan, Illinois, Ohio, Maryland and Virginia, deteriorating air quality has triggered health warnings affecting millions of people.

Why is air quality deteriorating?

The poor air quality is due to smoke from ongoing Canadian wildfires, which has been blown south by prevailing winds into large parts of the Great Lakes, Northeast, Mid-Atlantic and Midwest, according to the National Weather Service advisory.

Smoke contains PM2.5, microscopic particles less than 2.5 micrometers in diameter. Because these particles are extremely small, they can travel deep into the lungs and even enter the bloodstream, increasing the risk of respiratory and cardiovascular disease.

In some areas, there is also increased ground-level ozone, which further worsens air quality.

Which states are under an air quality alert?

National Weather Service bulletins show that warnings have been issued in several states, including:

Many warnings remain in effect through Friday, with some continuing into Saturday.

Where are the conditions worst?

Michigan

The Michigan Department of Environment, Great Lakes and Energy has issued a statewide air quality advisory through Saturday due to wildfire smoke.

Officials warned that conditions Friday could range from very unhealthy in southern Michigan to dangerous in northern parts of the state. The smoke is expected to linger until Saturday, with ozone pollution also a concern.

Pennsylvania has some of the strictest warnings.

The Pennsylvania Department of Environmental Protection has issued several Code Purple Alerts for:

A Code Purple alert means the air pollution is very unhealthy for everyone and residents are advised to avoid going outdoors.

The New York State Department of Environmental Conservation warned that air quality index (AQI) readings for fine particles could exceed 150, prompting an air quality health advisory until midnight.

Health officials urged residents — especially children, older adults and people with asthma or heart disease — to limit strenuous outdoor activities.

Illinois has declared Red Air Pollution Action Days in Chicago, Rockford and surrounding forecast sectors.

Officials said thick smoke from wildfires blanketing the Great Lakes region will keep AQI levels in the poor categories despite an expected improvement later in the day.

Maryland, Virginia and Washington DC

Several areas are under Code Purple or Code Red alerts.

Western Maryland, the District of Columbia, Winchester and parts of the eastern West Virginia Panhandle face purple alerts, while northern Virginia, the Maryland Piedmont, northern Baltimore and the Richmond metropolitan area are under red alerts.

Ohio issued a statewide alert warning that pollution could range from unhealthy for sensitive groups to dangerous, while West Virginia remains under a Code Red alert due to continued smoke from Canadian wildfires.

What do the different air quality alerts mean?

The Air Quality Index (AQI) is used to indicate the health risks posed by air pollution.

Code Orange: Unhealthy for sensitive groups such as children, older adults and people with heart or lung conditions.

Code Red: Unhealthy for everyone.

Code Purple: Very unhealthy, with increased health risks to the general population.

Hazardous (Maroon): Emergency conditions where everyone is at risk of serious health consequences.

Who is most at risk?

Health officials say wildfire smoke can affect anyone, but the following groups face greater risks:

Individuals with chronic lung disease

People with heart disease

Eye, nose and throat irritation

What measures do the authorities recommend?

Warning The National Weather Service advises residents to:

Stay indoors as much as possible.

Avoid strenuous outdoor activities.

Keep windows and doors closed.

Use air conditioning in recirculation mode if available.

Improve indoor air quality with portable air purifiers or HVAC filters rated MERV-13 or higher.

If outdoor exposure cannot be avoided, use a properly fitted N95 or P100 respirator.

Check local AQI forecasts before spending time outdoors.

People without access to air conditioning are advised to seek out cooling centers in case of dangerously high temperatures.

Why can Canadian wildfire smoke travel thousands of kilometers?

Wildfire smoke can be carried long distances by strong winds in the upper atmosphere. Large wildfires in Canada have repeatedly affected air quality across the United States in recent years, especially during the summer months.

According to the National Weather Service advisory, smoke from the current Canadian wildfires is expected to continue to affect several regions of the US through Saturday, although conditions may improve depending on changes in wind direction and weather.

Until then, health officials recommend minimizing outdoor exposure and closely monitoring local air quality updates.

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