Environment & Economy By Michael Hawthorne 559 Views

Chicago air is dirtier in July than smog-choked Los Angeles. More bad air is forecast.


After missing out on cleaner air during the coronavirus lockdown, the Chicago area just suffered its longest streak of high-pollution days in more than a decade.

Nine consecutive days of bad air swept through the region amid an emerging scientific link between exposure to pollution and COVID-19 death rates. Low-income, predominantly Black and Latino communities are being hit the hardest.

Air quality has been so poor, the entire Chicago area ended up dirtier than notoriously smog-choked Los Angeles during the beginning of the month, according to a Chicago Tribune review of federal data.

Satellites and land-based monitors tracked how unusually hot, sunny weather in the Midwest baked exhaust from automobile tailpipes, diesel engines and factory smokestacks into smog, also known as ground-level ozone.

Independence Day celebrations added to the problem. Stagnant air prevented soot pollution released by fireworks from dispersing, increasing the likelihood that even healthy people had trouble breathing during the holiday weekend.

Lake Michigan also played a role. Smog-forming pollutants — scientists call them precursors — collect over the lake on sunny days, then drift inland during late afternoons.

“If you have precursors cooking up in this sunny zone and then the lake breeze pushes all of that air back toward the shore, it can make for a really crummy day,” said Patricia Cleary, a University of Wisconsin at Eau Claire chemist involved in a federal study of smog sources and trends in Lake Michigan states.

The lake effect often leaves vacation spots like Door County, Wisconsin, and Saugutuck, Michigan, with more high-smog days than Chicago. But not so far this year.

Swells of lung-damaging, life-shortening pollution prompted the U.S. Environmental Protection Agency to classify seven of the first nine days of July as “unhealthy for sensitive groups” in Chicago and its suburbs, meaning children, older adults and people with lung or heart disease should limit outdoor activity.