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File photo: Visibility in downtown Philadelphia was greatly reduced by smoke drifting into the city from wildfires on June 7, 2023. (Kimberly Paynter/WHYY)
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As a trash fire burned at the WM transfer station in Philadelphia’s Grays Ferry neighborhood last week, an air quality monitor 1.5 miles south on Ritner Street did not pick up the smoke, according to an all-clear message public health officials posted two days later.
But a new sensor being tested at Stinger Square Park, just around 2,000 feet away from the fire, did detect a slight increase in levels of unhealthy air pollution, pushing the air quality index measured there from “good” to “moderate,” said Department of Public Health spokesperson James Garrow.
“Our monitor caught it immediately,” said Palak Raval-Nelson, Philadelphia public health commissioner.
This new Stinger Square Park sensor is part of a network of 76 air quality sensors throughout the city that public health officials have set up in recent weeks.
These monitors send hourly updates on levels of pollutants that can exacerbate asthma and other respiratory conditions to a new website, called Breathe Philly, which displays them as color-coded air quality indexes.
“Our focus is making sure that all Philadelphians have access to healthy and safe air,” Raval-Nelson said. “The way that we can make sure that the air is safe and healthy is to monitor it.”
The new sensors, purchased on a subscription basis from the air monitoring technology company Clarity for $90,000 per year, provide the city of Philadelphia with its most fine-grained look yet at air quality in neighborhoods. They measure fine particulate matter and nitrogen dioxide, common pollutants released from vehicle tailpipes, fossil fuel-burning power plants and other industrial facilities. The city has not signed a long-term contract for the sensors, but plans to continue paying for them for the foreseeable future, Garrow said.
The network is meant to fill in the gaps left by 11 federally mandated sensors that already measure pollutants such as ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide and particulate matter around Philadelphia. From 2018 to 2024, the city also collected data from a network of 50 street-level monitors in neighborhoods, but this data was not shared in real time due to the time needed to manually collect samples from these monitors and drive them to a lab for analysis, Raval-Nelson said.
Marilyn Howarth, who directs community engagement at the University of Pennsylvania’s Center of Excellence in Environmental Toxicology, said the 11 federally mandated monitors are meant to provide a regional picture of air quality, not describe the pollution that a person might experience standing on the ground.
“Many neighborhoods in the city really [did not] have any air monitors,” she said.
But the new network is much more dense. At least one of the new monitors is located within 1.5 miles of every address in the city, Garrow said.
City public health officials say the Breathe Philly website can help people with respiratory or cardiovascular conditions make their own decisions about when to avoid strenuous activity outside, close windows or stay indoors.
Raval-Nelson said the city made sure to place sensors throughout Philadelphia, especially in areas that have “always faced more environmental burdens than environmental goods.”
“You’ll have the information about the air that you’re breathing right at your fingertips, so you can make the right decision for your family,” Raval-Nelson said during Wednesday’s press conference. “Should you go outside and go to the park? Should you wait?”
Raval-Nelson said the new monitors will inform the city’s public health messaging during air quality emergencies, such as the Canadian wildfire smoke that blanketed the city in 2023, when she said public health guidance from the city was delayed.
Howarth hopes the new network will do a better job of detecting pollution during incidents such as the fire and series of explosions that occurred at the Philadelphia Energy Solutions refinery in South Philadelphia in 2019. Public health officials said after the explosion that the air was safe to breathe, based on handheld monitors and on-site monitoring systems.
“There were the large, black, billowing clouds that just so happened to be drifting toward New Jersey — basically across South Philadelphia — and didn’t actually pass over any of the [city’s stationary] air monitors,” Howarth said.
Garrow said the data the city collected at the time indicated no impact on the air quality within the neighboring community, and that the new network of monitors would provide a more detailed look during any similar situation in the future.
Still, the new monitors don’t measure every air pollutant. Howarth noted they don’t capture volatile organic chemicals or carcinogens. She also worries the hourly data updates could mask shorter-term spikes.
Howarth hopes the monitors will illuminate disparities in air quality between neighborhoods, created by the combination of traffic and industrial pollution.
“If someone lives in an intersection where there’s lots of idling cars, their air pollution may be significantly worse than someone living a few blocks away,” she said.
DeMorra Hawkins, a member of the environmental justice nonprofit Philly Thrive and longtime resident of Grays Ferry, said monitoring air quality is important, but it’s just one “piece of the puzzle.”
She said what the neighborhood actually needs is cleanup of environmental hazards, such as the former refinery site that’s currently being remediated and redeveloped as warehouses. She said the neighborhood also needs assets such as more green space, a health clinic and a pharmacy.
Hawkins is among a group of activists fighting a plan by the Children’s Hospital of Philadelphia to build a 1,000-car parking garage in the neighborhood, which they fear will bring more air pollution.
“The area I grew up in has been marginalized for over a century,” Hawkins said. “It’s not a secret.”
“Fix it,” she added.
Parker said the new, more detailed air quality data will help shape policy, but did not specify what policies her administration might pursue. Raval-Nelson added that the data could inform decisions, for example about tree planting or policies affecting mobile sources of air pollution, such as vehicles.