Why is the air quality so bad today? Wildfires worsen across the US

Wildfires have ravaged much of the West for years, but it seems the East may now have its share of fires as well.

Nationally, 27 large, uncontained wildfires are burning in 10 states, and multiple smaller fires are uncontrolled. As of Friday, wildfires have burned more than 2.16 million acres across the country, according to the National Interagency Fire Center.

With fire comes unhealthful smoke, which also threatens air quality for much of the U.S.

Wildfire smoke blankets much of the East

Many of the areas experiencing wildfire smoke will see moderate air quality for the next several days, according to the U.S. Air Quality Index.

At the same time, the western and eastern U.S. will have highs in the 90s, and the humidity will make it feel much warmer. Scorching temperatures and pollutants are expected to mix and create "moderate" and "unhealthy" ozone.

But the Environmental Protection Agency still advises people to limit exposure by taking pauses and, if possible, choosing less demanding activity, especially those with respiratory disorders such asthma or those who are active for six hours or more each day.

Unable to view our graphics? Click here to see them. 

More:Wildfires in New Mexico burn thousands of acres

Where the air quality is worst in the US

Air quality will worsen as wildfires produce more smoke. Airnow.gov predicts Saturday's air quality index will range from moderate to unhealthy in several parts of the country:

More:Smoke from Canadian wildfires brings poor air quality to Minnesota Monday, alert issued

How can wildfire smoke hurt you?

Smoke can cause a range of health problems, from minor irritations to serious concerns.

Depending on what's burning – grasslands, trees, vegetation or buildings – wildfire smoke can contain toxic chemical substances such as carbon monoxide, carbon dioxide, acid gases, sulfur dioxide, nitrogen oxides, benzene, toluene, styrene, metals and dioxins, says the New York State Department of Health.

Smoke can become more toxic the longer it lingers in the air. It can combine with trace radicals, or molecules with unpaired electrons, in a process known as oxidation. That process converts the particles into something known as free radicals, which can damage cells and tissues.

Smoke can also hamper what's called the macrophage function, the ability of lungs to protect themselves. Macrophages are white blood cells that aid the immune system.

States most at risk of fire danger

With persistent dry weather, much of the western states have an extreme risk of wildfires. Parts of the eastern U.S. also will be at risk of wildfires.

AccuWeather meteorologists don't expect a record-breaking fire season this year, but Americans may still face widespread dangers to air quality like they saw last year.

SOURCE AirNow.org; AccuWeather, NOAA; Environmental Protection Agency; California Air Resources Board, Windy.com and USA TODAY Network reporting and research