CINCINNATI — Canadian wildfires, which last year burned a record 45.7 million acres from coast to coast, are still burning. They’ve just gone underground. So when and if these so-called “zombie” wildfires reemerge, will that signal the return of poor air quality from their smoke blowing through Ohio? Here’s what to know. …Smoke from last year’s wildfire season in Canada drifted across the US from New England to Florida and across the Midwest. In Ohio, wildfire smoke in Akron created worse air quality than Beijing and Shanghai, cities notoriously plagued by air pollution. At the time, huge swaths of the Midwest had unhealthy air quality, including most or all of Iowa, Wisconsin, Illinois, Indiana, Ohio, Michigan and Pennsylvania.