Environment Canada’s poor air quality warning in Toronto due to wildfire smoke could stick around until the end of the week, said a meteorologist. In a yellow-level air quality warning, the federal weather agency says smoke from forest fires in northwestern Ontario is causing poor air quality and reduced visibility. The smoke is affecting much of southern Ontario. The poor air quality began Tuesday night and may last through to Thursday, the weather agency says. The warning comes as the city remains under a yellow heat warning. Toronto ranked first in a list of the world’s most polluted cities as of Wednesday morning, according to a global ranking by IQAir, a Swiss air quality technology company. “The air quality values have spiked quite high due to the particulate matter from that forest fire smoke,” said Environment Canada meteorologist Brian Owsiak.