A resident walks along the harbour in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

The city skyline is shrouded in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

A tourist looks at the harbour in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

Buildings are seen in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

Tourists take photos at the harbour in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

People walk along the harbour in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)

A ferry is seen travelling on the water in heavy smog in Vancouver, British Columbia, Canada, Sept. 13, 2020. As smoke from U.S. wildfires continues to blow north towards Canada, Vancouver on Sunday was among the top five major cities in the world for bad air quality according to Air Quality Index (AQI). (Photo by Liang Sen/Xinhua)