Researchers found that wildfire smoke can raise ozone to dangerous levels, posing hidden health risks even in remote areas.

The smoke floating over the border shared between America and Canada is now impacting air quality in states as far south as Texas, AirNow's data shows. The EPA has declared the air quality in states near the Canadian border as "unhealthy or "unhealthy for sensitive groups."

Here's why the Canadian wildfire smoke is returning to the state and what to know about the latest air quality advisory.