The presence of wildfire smoke from North America over the UK, whilst not common, does occasionally happen during the summer months.
Large plumes of smoke that rise from intense fires, that can burn for weeks on end, sometimes reach the upper atmosphere to be picked up by the jet stream - a zone of strong winds, close to the level at which planes fly. These winds then carry the smoke particles across the Atlantic.
Over recent weeks numerous fires have raged across many Canadian provinces, especially Manitoba and Saskatchewan forcing mass evacuations and triggering health alerts across Canada and the United States.
Here in the UK, the smoke plume is at too high an altitude to affect our air quality.