Pollution caused a noticeable haze over the Philly skyline on Monday

You might be able to see it if you catch a skyline view: there are more small particles in the air than usual in Philadelphia.

Air quality wasn’t great in the region Sunday, and the same is true on Monday. The area from Wilmington to Trenton is notching an air quality rating (AQI) of 123 — classified as “unhealthy for sensitive groups” by the Environmental Protection Agency.

That’s probably because of the unseasonably warm weather and something called temperature inversion, said Sean Greene, air quality programs manager at the Delaware Valley Regional Planning Commission.

It likely has nothing at all to do with the road closures or rallies that surged through Philadelphia after Joe Biden was declared president-elect, he clarified.

When we’re outside, Greene explained, we can breathe in these tiny specs of dust, emissions, metal and water vapor floating in the air. They can enter our lungs and even our blood stream, causing bodily damage.

It can pose serious problems for people with breathing disorders or lung or heart disease. It can also make them more susceptible to catching a respiratory infection. Yeah, not good when we’re in the middle of a respiratory pandemic that’s cresting a fall surge.

No reason to panic, Greene insisted. He suggested people sensitive to this sort of thing take special care to listen to their bodies.

“It becomes very important in this time,” Greene said. “What it means is, be aware that it’s an orange day, plan your activities accordingly and be aware of your body.”

Exercise indoors if you’re sensitive

On a good day, the AQI for Philly will linger somewhere in the 0 to 50 range. So the 100+ ranking we’re seeing today is eyebrow-raising.

(By comparison, Philadelphia is usually pretty clear: Los Angeles has an average AQI of around 60, but the city’s number jumped to 153 during wildfires in the fall. The average AQI in Shanghai is 109.)

Just because Phillly’s got a high AQI today doesn’t mean people who are sensitive — including children, older residents, and people with breathing disorders or heart or lung disease — will immediately suffer an asthma attack when they go outside.

It’s more like, if you’re already vulnerable, and you’re exercising outdoors in the middle of the day, you might suffer shortness of breath.

So if you have a breathing disorder, you might consider refraining from strenuous activity outdoors today — but sitting or walking outside should be just fine.

“If you know it’s going to be an unhealthy day for you, be very aware of how your body is reacting,” Greene said. “And if you feel shortness of breath, then take it easy.”

Downside to 70-degree November weather

You can attribute Philly’s poor AQI to a phenomenon called temperature inversion. During a typically colder time of year — like, say, the middle of November — the ground is already at a lower temp.

If the mercury gets unseasonably high, then the warmer air swirling in acts as a cap on the colder air at the ground level, Greene explained. Instead of all the usual particulate matter circulating up, up and away into the atmosphere, it’ll stay confined in the region in the pocket of warmth.

That means there’s a higher concentration of particles in the air at ground level, and a higher likelihood that you’ll breathe some in.

This specific situation happens roughly twice a year, Greene estimated.

“It’s pretty specific to this thermal condition,” he said. “Our long-term forecast for tomorrow is already back in the moderate range.”

Not like Memorial Day or Fourth of July

Some folks online wondered if today’s poor air quality had to do with the week of city-mandated overnight road closures that diverted buses, combined with the weekend of events in Center City, when thousands of Philadelphians marched through the street to protect and then celebrate the results of the presidential election.

That’s not likely, per Greene.

Though sometimes celebrations do factor into pollution, those instances look a lot different than this weekend.

Greene said on summer weekends like Memorial Day or the Fourth of July, when the entire region drives to the shore in droves, environmental professionals sometimes see spikes in pollution.

Not so when it’s just a few hours of overnight bus diversions, or smaller groups of people marching mostly on foot,

“They might have localized impacts,” Greene said. “But it’s not just Philadelphia, it’s a region-wide problem we’re having [with air quality]. The issue is a little bit larger than that.”

Michaela Winberg is a general assignment reporter at Billy Penn. She covers LGBTQ people and culture, public spaces, and transportation and mobility. She also sometimes produces radio and web features...