Wildfire smoke is a growing threat. Pittsburgh’s industrial pollution compounds the risk.

The wildfire smoke that blanketed Pittsburgh in July has cleared. But the health threat it exposed remains.

Smoke from Canadian wildfires pushed Allegheny County’s air quality into the maroon range July 16, meaning the pollution posed a hazard to everyone rather than only children, older adults and people with certain health conditions. County officials urged residents to limit their time outdoors.

For people with asthma and other respiratory conditions, the microscopic particles in wildfire smoke can trigger attacks, worsen breathing and lead to emergency care.

Climate scientists expect severe wildfire smoke to affect communities far from the fires with increasing frequency. In Pittsburgh, health and air quality experts warn that those episodes will arrive on top of a persistent local problem: industrial pollution that has contributed to elevated asthma rates and left some residents particularly susceptible to another surge of dangerous particles.