A big swath of the U.S. is under red and purple air quality alerts from Canada's smoke

As the sun rose on Madison, Wis., Thursday morning, the air quality was measured at 242 — a "very unhealthy" purple alert rating — due to smoke from Canada's wildfires.

Madison wasn't alone: from Cedar Rapids, Iowa, to Columbus, Ohio, a swath of the Midwest was marked by a dense mass of purple dots on the U.S. AirNow fire and smoke map, signaling the need for people to limit their time outside.

The purple blots swam in a sea of red alerts from smoky air blowing down from Canada, stretching from Rochester, Minn., to Richmond, Va.

Poor air quality is being reported over a huge area, with orange, red and purple alerts issued in parts of the Mississippi Valley, Great Lakes, Ohio Valley, Central Appalachia, Mid-Atlantic, and Northeast on Thursday.

"This week, the average air quality is expected to fluctuate between unhealthy for sensitive groups to unhealthy for everyone," member station Michigan Radio reports, citing state meteorologists.

Some of the health warnings apply to cities; others to entire regions. The entire state of Pennsylvania is under a code red action alert Thursday.

"On a Code Red Air Quality Action Day, young children, the elderly, and those with respiratory problems, such as asthma, emphysema, and bronchitis, are especially vulnerable to the effects of air pollution and should avoid outdoor activities, and everyone else should reduce prolonged or heavy exertion," according to the Pennsylvania Department of Environmental Protection.

Under the more serious "code purple" conditions, officials warn, vulnerable people should avoid all physical activity outdoors, and everyone else should avoid any prolonged or heavy exertion outdoors.

All of New York and New Jersey are under air quality alerts, the National Weather Service said, ranging from orange to red alerts.

Because smoke and wind patterns can change quickly in very localized areas, the AirNow agency recommends entering your zip code on its website to learn the latest related alert levels.

The dire alerts are hitting many areas that were recently under red and purple alerts in early June. As Washington, D.C., issued a new code red alert early Thursday, the unhealthy conditions prompted organizers of the Smithsonian Folklife Festival to cancel Thursday's opening ceremony.

Five U.S. cities — Washington, Chicago, Detroit, Minneapolis and New York — were among the 10 major cities worldwide with the worst air quality and pollution Thursday, according to international air quality monitoring website IQAir.com.

Canada is currently listed as having 503 active wildfires burning, and more than half of them (258) are out of control, the Canadian Interagency Forest Fire Centre said late Wednesday. That figure is up from around 450 fires that were burning in mid-June.

Smoke from the wildfires reached Europe this week, but because it's at a higher altitude in the atmosphere, the haze is mainly causing darker skies rather than health alerts.

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