Canadian smoke persists over Philly, with a ‘code orange’ air-quality alert

The region is about to get a real summer hors d’oeuvre, complete with an air-quality alert courtesy of Canadian wildfire smoke.

With temperatures creeping toward 90 degrees Wednesday and the milky veil of smoke persisting over the region, the Delaware Valley Regional Planning Commission has declared a “code orange” advisory for the Philadelphia region.

It is recommending that people with heart, respiratory, and related health issues limit time outdoors.

The combination of the warmth and the smoke “will lead to rapid ozone development” during the late morning and peaking in the afternoon, according to the Pennsylvania Department of Environmental Protection.

The alert covers Philadelphia and its seven neighboring counties in Pennsylvania and New Jersey.

 It is also in effect for all of Southeastern Pennsylvania, areas along the I-95 corridor from the Delaware border through Connecticut, and the New Hampshire and Maine Atlantic coasts. Similar alerts are in place for Iowa and portions of Michigan and Minnesota.

While the skies over Philly continue to look as if they need a good scrubbing, this marks the first air-quality alert since the smoke arrived over the weekend. The latest forecast from NOAA’s Global Systems Laboratory has a smoky encore Thursday.

But this episode in all likelihood will not come close to rivaling the Canadian smoke invasion of early June 2023, when the acrid odor was so thick that 911 centers were flooded with calls reporting fires, said Ray Martin, a lead meteorologist at the National Weather Service office in Mount Holly.

At midmorning Wednesday, the air quality in Philly still was classified as “moderate,” with ozone the prime pollutant, according to AirNow, a partnership of government and air-quality agencies.

The fires in the Canadian woodlands have resulted in the evacuations of thousands of residents. (So who are we to complain about the smoke shutting off any chance of seeing the northern lights?)

Natural Resources Canada reported that as of Friday more than a million acres of woodland were burning — more than double the average — across the country, the majority in western areas.

That has been the source region of the smoke, which has touched off health alarms in several U.S. cities — and a source region of Philadelphia’s cool, dry weather earlier this week borne by winds from the northwest.

Aesthetics aside, for the most part the smoke over the Philly region has been benign, unlike the June 2023 smoke-out that originated in northeastern Canada.

That smoke generated a rain of “hazardous” particulates that induced schools to go to virtual instruction. Those with background health conditions were advised to stay inside. Trash collections were pushed back, and the Phillies postponed a game.

Along with primary pollutants, such as particulates, that the smoke releases into the atmosphere, they can help produce ground-level ozone “through complex chemical process that are still not fully understood,” according to NOAA scientists.

The American Lung Association notes that research has documented that smoke that is days old and more than 1,000 miles away from its source can still promote ozone formation.

Ground-level ozone is not to be confused with the benign variant that helps protect earth from harmful ultraviolet radiation.

Prime ingredients for ground-level included emissions and solar heat, something the region is going to experience Wednesday.

Temperatures Wednesday are forecast to climb well into the 80s and perhaps flirt with 90 degrees. That would be several degrees above Tuesday’s high; of more significance, however, will be the increase in water vapor in the atmosphere.

The dew points, the absolute measures of moisture levels in the atmosphere, are going to shoot up to summerlike levels. Moisture in the air inhibits sweating and makes the body work harder to keep cool.

All thermal comfort being relative, the changes may require some acclimation, Martin said.

Temperatures during the last two weeks have been significantly below normal in Philadelphia, and premature heat has been scarce.

Martin said that people, even in the weather office, have complained in the last few years that spring around here has become the phantom season; how the weather appears to make abrupt jumps to summer.

“This season is different,” he said. “For those who like spring, they got it this year.”

That is all the more reason, he said, to exercise a degree of caution come Wednesday.

“Our bodies are in a different place in August, vs. June,” he said.

Said Tom Kines, senior meteorologist with AccuWeather Inc., with the taste of summer, “a lot of people are going to be happy. But it’s going to be a shock to the system.”