Air quality has taken a serious hit across the United States as a two-fold blow of wildfires in the West and in Canada have sent smoke pouring across large sections of the country — a problem that’s set to linger for days.

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

Smoke from western wildfires will drift into Colorado, creating hazy skies and lowering air quality at times.