Wildfires across the western United States and Canada put millions of people under air quality alerts Sunday as thousands of firefighters battled the flames, including the largest wildfire in California this year. The so-called Park Fire had scorched more than 550 square miles (1,430 square kilometers) of land in inland Northern California as of Sunday morning, darkening the sky with smoke and haze and contributing to poor air quality in a large swath of the Northwestern US and western Canada. Although the sprawling blaze was only 12% contained as of…