While, in general, ventilation is a helpful way to exhaust polluted indoor air and replace it with fresher outdoor air, there are times when it’s a bad idea; notably when outdoor air is dirtier than indoor air.

The American Lung Association published its 2022 Most Polluted Places list, concluding: “You can protect yourself by checking the air quality forecasts in your community and avoiding exercising or working outdoors when unhealthy air is expected”—and, we would add, by reducing or avoiding ventilation.