PHOTOS: Air pollution cloaks the eastern US

Cities across the East Coast were blanketed with hazy and smoky conditions this week from fires burning across Canadian territory.

The Air Quality Index (AQI) in New York City, Philadelphia and Washington, D.C., rivaled many cities with the worst average air quality around the world on Wednesday and Thursday.

The low visibility has delivered stunning visuals of key buildings and monuments obscured by darkened skies:

Tourists are seen at the World War II Memorial in Washington, D.C. The Air Quality Index was 308 at 11 a.m. as wildfires raging in eastern Canada spread dangerous levels of pollution across several U.S. metros. (Greg Nash/The Hill)

Washington, D.C., is seen through the haze from the Iwo Jima Memorial in Arlington, Va. The Air Quality Index was at 241 at 9 a.m. while wildfire smoke from Canada continues to come down through the East Coast. (Greg Nash/The Hill)

The Washington Monument clocked in smog for a second day in a row. About 98 million people in parts of 18 states from New Hampshire to South Carolina were under air quality alerts Wednesday for both wildfire smoke and ozone. (Greg Nash/The Hill)

The pillars of the Lincoln Memorial cut through a background of smoke fogging the National Mall as tourists visit the landmark. (Greg Nash/The Hill)

The Reflecting Pool mirrors smoke clouding the Washington Monument as Washington, D.C., faces “code purple” air quality. (Getty Images)

Smoky, throat-choking air from the hundreds of Canadian wildfires darkened skylines New York and other major American cities, prompting officials to urge residents to remain indoors. (Getty Images)

New York City topped the list for the world’s worst daily air pollution. Unhealthy air quality can lead to health problems, especially for those in sensitive groups including children, the elderly and those with respiratory issues. (Getty Images)

The Environmental Protection Agency said hazy skies, reduced visibility and the odor of burning wood is “very likely” to continue in the northern states for days as the wildfires continue to burn. (Getty Images)

A fuzzy City Hall backdrops commuters moving along Broad Street in Philadelphia while smoke continues to push south and west. (AP Photo/Matt Slocum)

A cyclist rides in front of the Philadelphia skyline enveloped in a dystopian haze as Philadelphia hits a “code purple” air quality index at 212. (AP Photo/Matt Rourke)