Growling engines and squealing brakes are an integral part of the allure of auto racing.

       In less than a week, Chicago will host its first NASCAR street race where elite stock cars that average around 5 mpg in a typical race will be hitting speeds over 100 mph downtown.

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       As race cars turn and brake, as tires screech, fine particulate matter is released into the air. And unlike commuter vehicles, race cars aren’t required to have pollution control devices that filter exhaust gases.

       Among the 25 most polluted cities in the country, Chicago has plenty of its own air quality problems. In addition to factory and local vehicle emissions, pollutants from Canadian wildfires have regularly obscured the skyline over the past month and reached unhealthy conditions for everyone Tuesday. On July Fourth, the city will let loose with fireworks that can introduce, on a national average, 42% more pollutants into the air than are found on a normal day.