Toxic wildfire smoke is choking millions of Americans on Thursday.
Air quality alerts have been issued across 14 states as a thick plume from Canadian wildfires pours into the Midwest and Northeast.
The affected states are Minnesota, Michigan, Illinois, Indiana, Ohio, Pennsylvania, West Virginia, New York, Vermont, New Hampshire, Massachusetts, Connecticut, Rhode Island and New Jersey.
Detroit ranked as the most polluted major city in the world Thursday morning, recording a hazardous live Air Quality Index (AQI) of 426, as Minneapolis ranked third with an AQI of 349. Good AQIs range from 0 to 50.
Officials have warned that wildfire smoke contains fine particulate matter, also known as PM2.5, which consists of microscopic particles of toxic compounds, small enough to penetrate deep into the lungs and enter the bloodstream.
The US Environmental Protection Agency (EPA) has connected breathing in PM2.5 to multiple health issues, including aggravated asthma, decreased lung function, irregular heartbeat, heart attacks and premature death for those with heart and lung disease.
Most alerts remain in place until midnight Thursday, while warnings across Minnesota are expected to continue until 11am Friday and could be extended if dense smoke persists.
‘Any exposure to the air, even for a few minutes, can lead to serious health effects on everybody,’ Plume Labs, which tracks and forecasts air pollution, said. ‘Avoid outdoor activities.’
Air quality map: Orange is unhealthy for sensitive groups, red is unhealthy, purple is very unhealthy and maroon is hazardous
In New York City, PM2.5 concentration is 7.8 times higher than what is deemed safe by the World Health Organization
The sprawling emergency comes as hundreds of wildfires continue burning across Canada, sending smoke across the border and into densely populated sections of the US.
Michigan is under a statewide air quality alert after plumes from Canadian wildfires spread through the Upper Peninsula and continued sinking south toward the Indiana border.
State officials said pollution could range from unhealthy for sensitive groups in southern Michigan to unhealthy farther north, with hourly concentrations potentially reaching very unhealthy or hazardous levels.
The warning covers major population centers, including Detroit, Ann Arbor, Flint, Grand Rapids, Lansing, Kalamazoo, Saginaw, Traverse City, Marquette and communities throughout northern Michigan.
Residents were urged to avoid strenuous outdoor activities and watch for wheezing, coughing, dizziness, chest tightness or burning in the eyes, nose and throat.
Officials also recommended closing windows and running central air conditioning with a MERV-13 filter or higher, where available, to reduce the amount of smoke entering homes.
Conditions are also severe in Minnesota, where portions of the state have reached the maroon, or hazardous, category.
The Minnesota Pollution Control Agency said dense smoke had already produced hourly readings that surpassed previous records in the Twin Cities, while trace amounts of ash had been observed.
The smoke blowing into the US stems from more than 100 wildfires currently blazing in Canada
In northern Illinois, the state Environmental Protection Agency declared a red air pollution action day for Rockford and all six Chicago-area forecast zone
Michigan is under a statewide air quality alert after plumes from Canadian wildfires spread through the Upper Peninsula and continued sinking south toward the Indiana border. Pictured is a shot from the shores of Lake Superior
Officials warned that everyone was likely to be affected by the pollution in central and northeastern Minnesota and advised the general public to avoid all outdoor physical activity.
Authorities advised people in affected areas to monitor local air-quality readings throughout the day because conditions could worsen rapidly as the plume shifts.
Northwestern areas were expected to experience purple, or very unhealthy, conditions, while southern and southeastern Minnesota faced red-level pollution as smoke moved along a nearly stationary front.
The sharp edge of the plume meant that air quality could vary dramatically within the same county, with some locations experiencing relatively clean air while nearby communities endured unhealthy conditions.
In northern Illinois, the state Environmental Protection Agency declared a red air pollution action day for Rockford and all six Chicago-area forecast zones.
The National Weather Service (NWS) said the region was sitting on the edge of a thick plume of surface smoke moving south from Canada, although uncertainty remained over how far it would advance.
Chicago, Evanston, Joliet, Aurora, Naperville, Waukegan, Rockford and surrounding communities were included in the alert, which was scheduled to continue until midnight Thursday.
Michigan is experiencing the worst of the wildfire smoke, leaving drivers unable to see
Everyone in those areas was told to reduce prolonged outdoor activity or heavy exertion, while children, older adults and people with respiratory illnesses were advised to avoid it.
Neighboring parts of Indiana, including Lake, Porter, Newton and Jasper counties, were placed under an air quality action day because PM2.5 was expected to reach the unhealthy range.
The alert included Gary, Hammond, Merrillville, Portage, Valparaiso and communities immediately south and east of Chicago.
Ohio issued an advisory for the entire state, warning that Canadian wildfire smoke would push air quality into the unhealthy-for-sensitive-groups category.
Buffalo, New York’s skies turned orange on Wednesday, with wildfire smoke still lingering today
Meteorologists share several images of Buffalo on Wednesday, showing brown skies from the smoke traveling into the US from Canada
Northeastern Ohio faced some of the most dangerous conditions, with a maroon alert issued for counties around Cleveland, Akron and Lake Erie.
Authorities warned that pollution at that level could be extremely hazardous for the general population and that minimizing exposure could be difficult even indoors.
Pennsylvania was placed under a statewide Code Red alert, unhealthy for everyone, on Thursday as smoke from Ontario and Minnesota moved into the state from north to south.
Officials said everyone could experience health effects, while members of sensitive groups faced the possibility of more serious problems.
The smoke was expected to linger into Friday, when Pennsylvania’s alert was forecast to ease to Code Orange, which will be unhealthy for sensitive groups.
New York issued fine-particle advisories across much of the state, including New York City, Long Island, the Hudson Valley, Albany, Syracuse, Buffalo, Rochester and communities near the Canadian border.
Forecast AQI readings exceeded 200 in parts of western New York, placing the pollution in the very unhealthy category.
Alerts also stretched across New England, covering all or portions of Vermont, New Hampshire, Massachusetts, Connecticut and Rhode Island, as well as northern New Jersey.
West Virginia’s northern counties, including communities around Wheeling and Weirton, were also placed under a Code Orange alert specifically because of elevated particles from Canadian wildfire smoke.
