Millions in the US remain under dire air quality warnings as wildfire smoke from Canada makes the air worse for your health than smoking a dozen cigarettes a day. The situation has deteriorated to the point where major metropolitan areas, including Chicago, Detroit, Washington and New York are now ranked as the worst polluted cities in the world on Friday. The National Weather Service has issued air quality alerts in 16 states, stretching from Minnesota, Wisconsin, Michigan and Illinois in the Upper Midwest to New York, New Jersey, Maryland and Virginia along the East Coast. According to the EPA, the air is now considered 'hazardous' from northern Minnesota to Columbus, Ohio - the agency's most severe air quality rating. Officials with NWS urged anyone in areas where the air quality has reached this levels to 'avoid all physical activity outdoors.' The wildfire smoke pouring down from hundreds of forest fires in Canada, mainly in the province of Ontario, is filled with microscopic pollutants called fine particulate matter, or PM2.5.

These are toxic compounds typically created by burning wood or industrial pollution, which are small enough to penetrate human tissue and cause severe breathing issues or even death among people with heart and lung disease. Health officials have noted that breathing in PM2.5 in the amounts currently seen in Detroit (292.6 µg/m³) on Friday equates to smoking more than 13 cigarettes in a single day. According to live air quality-tracking website IQAir, Chicago's air is currently filled with more than 240 µg/m³ (micrograms per cubic meter) of PM2.5 pollution - the equivalent of smoking more than 10 cigarettes in a day.

Berkeley Earth, a nonprofit research organization known for analyzing climate and air quality data, estimated that breathing air with 22 µg/m³ of PM2.5 pollution for one full day has roughly the same long-term impact as smoking one cigarette. Dr Jonathan Tan from the Children’s Hospital of Philadelphia told AccuWeather: 'When the AQI climbs into the 150+ range for a full day outside, that’s in the ballpark of [smoking] seven to nine cigarettes.' Typically, the Air Quality Index (AQI) is measured on a scale from 0 to 500: 'good' (0–50) carries little risk, 'moderate' (51–100) may affect sensitive individuals, 'unhealthy for sensitive groups' (101–150) poses increased risk and 'unhealthy' (151–200) impacts everyone, limiting outdoor activity.

When outdoor air quality reaches the 300 to 500 'hazardous' zone or surpasses that mark, the EPA warns that everyone should avoid all physical activity outside. As of 9am ET on Friday, both Detroit and Chicago had surpassed 380, according to IQAir. Washington DC registered at 247, the third-worst polluted major city on the planet, and New York was fourth at 165 - all in the unhealthy to very unhealthy ranges. The growing plume of pollution-filled smoke has been blamed on Canada's lack of fire management services, which has now let roughly 800 wildfires burn through over two millions acres of land throughout the country this year.

Dan DePodwin, AccuWeather's vice president of forecasting, told the Daily Mail: 'Because a lot of Canada is very rural, in many parts of the country, they don't actively fight fires, because there is very little to no population nearby.' 'So, the fires burn until they go out themselves, or they do minimal fire suppression. So that is part of it, that is occurring here,' he continued. The situation has drawn the ire of US lawmakers, who slammed the Canadian government's alleged inability to contain the wildfires and the smoke reaching the northern US.

Congressman Nick Langworthy of New York said: 'Americans should not be forced to breathe hazardous air year after year because Canada refuses to properly manage its forests.' 'This is no longer a one-time emergency - it’s becoming an annual public health crisis. That is unacceptable,' added Langworthy, who represents parts of Buffalo, which has been severely impacted by the toxic air crisis. Congressman Bill Huizenga of Michigan also called on the Canadian government to work with the US on finding a solution to the annual wildfire problem north of the border. 'Michiganders must stop paying the price for bad policy,' Huizenga declared.

NWS officials also urged anyone considered to be in a 'sensitive group' to poor air quality to remain indoors with the windows shut on Friday. These groups include the elderly, young children, pregnant women and those with chronic health problems such as heart and lung disease. 'If you don`t have an air conditioner, staying inside with the windows closed may be dangerous in extremely hot weather. If you are hot, go someplace with air conditioning or check with your local government to find out if cooling centers are available in your community,' the agency recommended. 'Make sure to keep pets indoors to limit their exposure to poor air quality,' the AccuWeather team added in a statement.