How bad are Canadian and US wildfires, and what is the air quality risk?

How bad are Canadian and US wildfires, and what is the air quality risk?Image source, Cole Burston/ AFP/Getty ImagesImage caption, Wildfire smoke is expected to continue affecting air quality in Toronto and US cities throughout the weekByEsme Stallard, Senior climate and science reporter, Erwan Rivault, Senior data designer  and Pilar Tomas, Senior visual journalistPublished7 minutes agoCities across northeast Canada and the US are suffering from intense smoke brought on by wildfires burning across Ontario and Minnesota.Residents in New York, Boston and Toronto have been encouraged to avoid "strenuous activity" over potential health impacts caused by the pollution.Canada wildfires leave train 'encased in flames' as smoke drifts towards USPublished22 hours agoWhere are the wildfires and how did they start?There are currently 858 wildfires actively burning across Canada – nearly 200 of those in Ontario - according to the Canadian Interagency Forest Fire Centre.Along the northern edge of Minnesota there are 17 fires that are still burning and an emergency declaration is in place to help mobilise suppression efforts.In Ontario, the fires are north of Lake Superior in more remote parts of the province, but within or close to national parks and First Nation communities.So far, six communities are are under evacuation orders with reports of damage to properties. Grand Council Chief Linda Debassige said in a statement on Wednesday that the remote Namaygoosisagagun First Nation in northern Ontario was "devastated by an unexpected and fast-moving wildfire" that severely damaged homes and community buildings.Wildfires are very common in Canada, but the number of outbreaks has rapidly increased in recent weeks.The National Interagency Fire Centre in the US and Natural Resources Canada predicted this was likely, external because of sustained hot weather at the end of June across northern Ontario, and below average rainfall, external.This hot weather...