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Sep 19, 2023

Wildfires, pollution bring Chicago hazy skies, red sunsets

You may have been wondering about the recent vibrant, reddish sunsets and hazy

You may have been wondering about the recent vibrant, reddish sunsets and hazy skyline in Chicago. What's behind these phenomena can be traced back to a combination of particulate matter and smoke from Canadian wildfires and pollutants that create ground-level ozone.

These conditions have occurred before, as recently as last July when wildfires in the western United States caused red suns and moons and hazy skies to be visible across Illinois.

While the red sun and milky-looking skies might give the city an otherworldly, even awe-inspiring appearance, Chicagoans — especially those with respiratory or pulmonary disorders, as well as active children and adults — should take precautions.

"Why is the sky blue? Sounds like a philosophical question, but there's a real reason for it," said Trent Ford, Illinois state climatologist. "Sunlight comes into our atmosphere, and all of the stuff, for lack of a better term — the particulate matter, the aerosols, other types of liquids and solids in our atmosphere — scatter the light. Which means the light hits it, and it goes in all directions."

Because blue light has the shortest wavelength, it's scattered the most effectively. But a high concentration of particulate matter in the air, which may travel from faraway fires carried by the wind, allows longer wavelengths of orange and red light to scatter around as well. Recent dust storms have also caused vibrant, colorful sunrises and sunsets in the state as well.

Smoke from Canadian wildfires has been spreading across the region high up in the atmosphere. In addition to filtering the sunshine at times, this can result in spectacularly colorful sunrises & sunsets. This graphic from @NWSStateCollege explains why. https://t.co/Z5AeOA7Wli

Ozone is invisible, but the pollutants that produce it — particularly nitrogen oxides — can cause a brownish haze in the sky, according to Brian Urbaszewsk, director of environmental health programs at the Chicago-based Respiratory Health Association.

"You’re getting the smoke particles, but you’re also getting the nitrogen oxides," Urbaszewsk said. "So there's a bunch of overlapping circles here. So it's not one or the other … but I think it's pretty safe to say most of what is called visible air quality that people are noticing is wildfire-driven."

Ground-level ozone is different from the naturally occurring ozone layer found higher up in the atmosphere, or stratosphere.

It is produced when two types of pollutants — organic chemical compounds, which are produced in the manufacture of products like paint, pharmaceuticals and refrigerants, and nitrogen oxides from diesel and gasoline engines — react in sunlight. That means that ground-level ozone is produced more effectively and concentrates more in hot, dry and still weather.

And Chicago just had its driest May in decades, and the fourth driest ever.

[ Chicago weather: Lack of rain means driest May in almost 30 years. How gardeners, golfers and kayakers cope. ]

Natural ozone is beneficial because it protects humans from the sun's harmful ultraviolet rays. But ground-level ozone can have a variety of adverse impacts on human health.

Urbaszewsk said when a person inhales ozone, it chemically burns the throat, airways and lungs, which leads to swelling. This can cause shortness of breath, asthma attacks, coughing, chest pains and throat irritation.

A hazy skyline is visible from Chicago's Bucktown neighborhood on June 6, 2023. (John J. Kim/Chicago Tribune)

"Ozone was the main problem before this past weekend, as higher temperatures and a lot of sun and low winds simply cooked everything we were putting up already to make ozone," said Urbaszewsk. "Likely some of the smoke from … Canada helped generate more ozone, but we put up a lot of air pollution in the Chicago region as well as downstate that make a lot of ozone even without wildfires."

For Ford, these air quality issues in Illinois underscore "how connected things are."

The high-pressure system and stillness of winds have caused drought and helped increase ground-level ozone. The same atmospheric patterns are also bringing in dominant airflow from the wildfires thousands of miles away in Canada, which carries PM2.5, or particulate matter smaller or equal to 2.5 micrometers. For comparison, the width of a human hair is about 80 micrometers.

PM2.5 is produced by sources such as vehicle exhaust and industry emissions as well as forest fires.

In an average year to this date, a square mile would’ve been burned by wildfires in the Canadian province of Quebec. But this year, 600 square miles had already burned as of Monday. According to Quebec's fire prevention agency, this is the result of high temperatures and dry conditions.

These wildfires — more than 150 in Quebec, according to NASA — are having far-reaching consequences that cross borders and have affected states as far south as Virginia. The Illinois Environmental Protection Agency issued a statewide alert last week that air quality through Monday would be "unhealthy for sensitive groups."

The Illinois EPA provides daily air quality readings based on the Air Quality Index for 14 regions across the state. The index is a color-coded system that classifies air quality from good to hazardous.

According to the agency, the Chicago area's air ranked good only one day in the past two weeks. During that time, the main challenge was ozone smog, as Urbaszewsk said. But in the past few days, PM2.5 produced by wildfire smoke has been the main driver of air quality index readings, he added.

Skies may remain somewhat hazy for the rest of the week as the forecast shows air quality will remain at a moderate level through at least Sunday, with the primary pollutant in the area being PM2.5. As dry conditions continue in Illinois, the state is also at risk for drought and fires.

"Over time, the science has shown that it's really the smallest particles doing the most damage," mainly because the human body is not that good at filtering out really small particles, Urbaszewsk said. "They’re the most connected with bad health outcomes. They also go the deepest in the lungs."

Initially, particulate matter may cause burning eyes and a runny nose. But once in the deepest portions of the lungs, it can cross into the bloodstream, messing with blood chemistry and causing heart stoppages. Fine particulate matter has also been linked to premature births, diabetes and even dementia, Urbaszewsk said.

"There are deaths from ozone, and there are deaths caused by fine particulate matter. It's about 10 to 1," he said. "Ozone deaths have generally been in the few thousands a year nationally. When you’re looking at fine particulate matter-generated deaths from air pollution, it's tens of thousands. So it's much more dangerous."

Though projections indicate longer and more intense wildfire seasons in North America over the next few decades, Ford said, there's no way to say how this will affect air quality.

"What that means for our air quality here is really uncertain," he said. "I’ve seen some discussion of more wildfires in Western Canada or California — does that mean more of these kinds of days where we have high PM2.5? And it's really hard to say, it really depends on the atmospheric dynamics."

In order to reduce health risks when air quality readings show high concentrations of ground-level ozone or fine particulate matter, people can opt for less intense outdoor activities, shorten or take more breaks during outdoor activities, reschedule activities to the morning or evening when ozone is lower, or move outdoor activities inside.

Even if you’re inside, you should keep indoor air clean. Don't use wood fireplaces, gas logs, gas stoves or candles, and don't smoke. Don't vacuum, either, since that stirs up particles that are already inside. Run the air conditioner if you have one, keeping the fresh air intake closed and the filter clean.

"Knowledge is power, basically," Urbaszewsk said. "So take it easy, stay hydrated, don't overexert yourself. Especially on that day. And of course, follow your doctor's advice in terms of medication and other things."

Citizens can stay up to date regarding air quality in their area by visiting the U.S. EPA's AirNow.gov website. They can also sign up for daily and real-time air quality alerts at enviroflash.info.

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