Canadian wildfire smoke puts Philly under "Code Red" air quality alert

Driving the news: Philadelphia's "Code Red" air quality alert is in effect until at least Friday.

• The city's Air Quality Index reached the "very unhealthy" range on Thursday.
• City health officials are monitoring conditions to determine when the alert can be lifted.

Zoom out: More than 800 fires are burning across Canada, including several near the Minnesota border.

• Pennsylvania is also under a "Code Red" advisory.

What they're saying: While air quality can vary by neighborhood, city officials are advising residents to avoid strenuous outdoor activity.

• "Today is not the day to start your marathon training plan," Philadelphia Health Commissioner Palak Raval-Nelson said in a statement.

What's ahead: Philadelphia's air quality is expected to improve to "Code Orange" on Friday, National Weather Service meteorologist Sarah Johnson tells Axios.

• But changing weather patterns make it difficult to predict conditions for later this weekend.

For those who must be outside: Health officials advise wearing a mask, such as an N95 or KN95, and taking frequent breaks indoors.

• They also recommend closing windows and doors and either turning off air conditioners that draw in outside air or switching them to recirculation mode.
• Also avoid burning candles, frying foods or vacuuming, which can increase indoor particle pollution.