Wildfire Smoke Blankets Sky Across New York, Other States, Prompting Air-Quality Warnings

Millions of Americans inhaled unhealthy air for a second straight day Wednesday, as smoke from hundreds of Canadian wildfires continued to cast haze over populous parts of the Midwest, mid-Atlantic and Northeast.

In New York, the most populated metropolitan area in the U.S., the air-quality level was 170 on Wednesday morning, an unhealthy level for a second consecutive day and surpassing levels of some of the most polluted cities on Earth, according to AirNow, a government tracking site.

An air-quality level above 300 is considered hazardous. An area near Syracuse, N.Y., reached...