PHOENIX Air Monitoring Project in Altadena Rises from the Ashes

In the wake of the Eaton fire, Caltech researchers working with community members, business owners, and schools in Altadena and Pasadena have quickly deployed a network of particulate air quality sensors on rooftops in and around the burned areas of Altadena. The network, dubbed PHOENIX (Post-fire airborne Hazard Observation Environmental Network for Integrated Xposure-monitoring), aims to provide the community with a way to monitor airborne dust as debris removal and rebuilding proceed.

Data from the PHOENIX sensors can be viewed here and are updated every five minutes.

"With phase-2 debris removal underway, we wanted to give the community a source of independent air-quality measurements," says Haroula Baliaka (MS '23), a graduate student in environmental science and engineering at Caltech who has been working to install the PHOENIX sensors. At the same time, the data can be used by agencies such as FEMA, the EPA, and the Army Corps of Engineers to gauge how well dust-mitigation efforts are working."

As of March 19, the team has installed 19 sensors spatially distributed across Altadena; one sensor was installed at NASA's Jet Propulsion Laboratory (JPL), which is managed by Caltech. For the past 4 weeks, Baliaka, Coleen Roehl, an associate research scientist at Caltech, and Nikos Kanakaris, a machine learning researcher, have been using their personal networks and reaching out to the community to identify standing structures with nearly flat roofs and then quickly going out to install sensors made by QuantAQ. These commercially available sensors offer the advantage of running on solar power and using cellular networks, whereas many other sensors require access to Wi-Fi. "That's helped us with setting up fast—within a few hours—and being able to already show the real-time data" Baliaka says.

The sensor locations include multiple school sites including the EF Academy, a private day and boarding high school in Pasadena; Odyssey Charter School; Saint Mark's School; and Saint Elizabeth Parish School. Sensors will soon be installed on at least two additional school sites in the Pasadena Unified School District. Parents at Crestview Preparatory School in La Cañada Flintridge raised funds to purchase a sensor for the school.

Each of the air quality devices is able to measure particulate matter in three size categories—particulates measuring less than 1 micrometer in diameter (PM1.0), those that are less than 2.5 micrometers (PM2.5) in diameter, and larger particulates up to 10 micrometers in diameter (PM10). Data related to these larger particles will be particularly useful as the region recovers from the fire, says Paul Wennberg, Caltech's R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, who spearheaded the PHOENIX project. The larger particles settle to the ground relatively fast compared to the smaller PM2.5 particles, which tend to stay aloft for days. "That means these larger particles are much more indicative of local dust events," Wennberg says. "Since one of our goals was to be able to isolate from the general aerosol pollution of Los Angeles things that were more related to the fire debris, we needed sensors capable of good PM10 measurements."

Although the large particles settle quickly, Wennberg says the air mixes them around and can carry them roughly a kilometer away. "If you have a dust source during the day and if it's made out of the ash and the dust from these houses, it will get transported some distance," says Wennberg. "So we're trying to place our sensors roughly a kilometer apart in every direction to be able to isolate and figure out where the dust is coming from."

While the PHOENIX website currently shows only raw data from the various sensors, the team plans to continue incorporating additional features to the site that will illustrate general air quality across Altadena and identify dust events. The team also aims to make the data as accessible as possible and to use machine learning and predictive models to gain additional insights.

Funding Enabled the Team to Spring Into Action

Before the fire, the air-quality map maintained by sensor company PurpleAir was dotted with sensors throughout the Altadena area. Green spots on the map correspond to locations of low-cost PurpleAir sensors bought and installed by residents, business owners, and community hubs, such as schools, forming a network driven by citizen science. Data from those sensors also feed into the EPA's data, helping to formulate the air-quality index (AQI) that is reported on the weather app on our phones, for example.

Immediately after the fire, Baliaka and Wennberg noticed with concern that the PurpleAir map was completely devoid of sensors in the Altadena burn zone. All the sensors had either been burned or were no longer receiving Wi-Fi and utility power needed to keep them running.

"We had lost this important data for everybody in the community," Wennberg says. "All those PurpleAir sensors had just evaporated."

At the same time, the researchers were seeing data from the ASCENT (Atmospheric Science and Chemistry mEasurement NeTwork) site that Baliaka helped set up in Pico Rivera. The suite of instruments there is one in a nationwide network of 12 aerosol measuring sites managed by Nga Lee (Sally) Ng (PhD '07) of the Georgia Institute of Technology. The Pico Rivera ASCENT site was measuring heightened levels of toxins such as lead and chlorine in the small particulate matter in the air coming downwind from the fire.

"We were looking at Haroula's data, seeing all this lead in the particulates in the air and just thinking what could we do to assist our community?" Wennberg says.

So when John Eiler, the Robert P. Sharp Professor of Geology and Geochemistry and the Ted and Ginger Jenkins Leadership Chair of Caltech's Division of Geological and Planetary Sciences (GPS), asked faculty in the division if they had fire-related projects in need of immediate funding, Wennberg, a GPS faculty member, quickly shot off an email. Between funds from members of the GPS Chair's Advisory Council and other supporters of the GPS division, along with support from the Resnick Sustainability Institute, the team quickly had enough funding to buy the first set of sensors. Loans of additional sensors for the network have come from JPL, from the Georgia Institute of Technology, and from the ASCENT network. The City of Pasadena is also purchasing a sensor to install on the roof of a Public Health Department building. QuantAQ donated a year of Caltech's two-year service contract to operate the sensors. Looking ahead, the team aims to further expand the network and enhance the public database to provide real-time access to particulate matter concentrations.

"It all came together so quickly," Wennberg says. "This seemed like something in our wheelhouse that could really help the community. But it was really Haroula who said, 'We have to do this.'"