Poor air quality returns to US north-east from Canada wildfires

New York City, parts of Pennsylvania and Baltimore all issued warnings as 421 wildfires continue to burn north of border

Poor air quality returned to the north-east US on Sunday, although it was nowhere near as bad as the heavy haze that recently shrouded the region and triggered global headlines as wind-borne smoke from raging Canadian wildfires caused orange skies, thick smog and record-setting pollutant levels.

On Sunday morning, a smoke plume moved across New York City, leaving the air quality index in the city at 103 and categorized as unhealthy for sensitive groups", particularly for those with heart or lung problems.