Wildfires in Canada, particularly in Quebec, are causing substantial air quality issues across the United States. As of Thursday, air quality alerts have been issued in 20 states, stretching from Missouri to Massachusetts. New York City experienced the worst air quality of any major city globally on Wednesday due to the smoke, with other cities like Washington, D.C., Philadelphia, and Columbus, Ohio, also reporting poor air quality. The wildfires, intensified by dry and warm conditions, have overwhelmed firefighting resources in Quebec. The smoke is expected to persist as it moves southward, impacting air quality in numerous U.S. metropolitan areas.