In the aftermath of the Eaton blaze, Caltech scientists collaborating with local residents, business proprietors, and educational institutions in Altadena and Pasadena have swiftly established a network of airborne particulate sensors on rooftops in and around the affected zones of Altadena. This system, referred to as PHOENIX (Post-fire airborne Hazard Observation Environmental Network for Integrated Xposure-monitoring), is designed to empower the community to track airborne dust levels as debris removal and reconstruction efforts continue.
Information gathered from the PHOENIX sensors is accessible here and is refreshed every five minutes.
“With phase-2 debris removal currently in progress, we wanted to provide the community with an independent source of air-quality data,” says Haroula Baliaka (MS ’23), a graduate scholar in environmental science and engineering at Caltech who has been instrumental in installing the PHOENIX sensors. Concurrently, this data can serve organizations like FEMA, the EPA, and the Army Corps of Engineers to evaluate the effectiveness of dust-mitigation measures,” she adds.
As of March 19, the group has positioned 19 sensors strategically across Altadena; one sensor has been set up at NASA’s Jet Propulsion Laboratory (JPL), which is overseen by Caltech. Over the past four weeks, Baliaka, Coleen Roehl, an associate research scientist at Caltech, and Nikos Kanakaris, a machine learning expert, have leveraged their personal connections and reached out to the community to find existing structures with nearly flat roofs, and then promptly installed sensors developed by QuantAQ. These commercially produced sensors are advantageous as they operate on solar energy and utilize cellular networks, whereas many other sensors depend on Wi-Fi access. “This has enabled us to set up quickly—within just a few hours—and already provide real-time data,” says Baliaka.
The sensor locations encompass several school sites, including the EF Academy, a private secondary school in Pasadena; Odyssey Charter School; Saint Mark’s School; and Saint Elizabeth Parish School. Plans are underway to install sensors at a minimum of two additional school sites in the Pasadena Unified School District. Parents at Crestview Preparatory School in La Cañada Flintridge have raised funds to acquire a sensor for their institution.
Each air quality device is capable of measuring particulate matter in three distinct size categories—particles smaller than 1 micrometer in diameter (PM1.0), those less than 2.5 micrometers (PM2.5), and larger particles up to 10 micrometers in diameter (PM10). Data on these larger particles will be particularly significant as the area recuperates from the fire, according to Paul Wennberg, Caltech’s R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, who led the PHOENIX initiative. These larger particles tend to settle more quickly compared to the smaller PM2.5 particles, which can linger in the air for several days. “Consequently, these larger particles provide a better indication of local dust occurrences,” Wennberg explains. “Since one of our objectives was to differentiate from the general aerosol pollution in Los Angeles those elements specifically linked to fire debris, we required sensors capable of accurate PM10 measurements.”
While the larger particles do settle rapidly, Wennberg observes that air currents can disseminate them up to about one kilometer away. “If a dust source emerges during the day and comprises ash and dust from the affected homes, it can be transported over a certain distance,” states Wennberg. “Thus, we are positioning our sensors approximately one kilometer apart in all directions to isolate and determine the origins of the dust.”
Although the PHOENIX website presently displays only raw data from the various sensors, the team intends to progressively integrate additional functionalities to the site that will showcase overall air quality across Altadena and identify dust incidents. The team is also committed to making the data as accessible as possible and plans to utilize machine learning and predictive models to derive further insights.
Funding Allowed the Team to Act Expeditiously
Prior to the fire, the air-quality map maintained by sensor manufacturer PurpleAir was populated with sensors scattered throughout the Altadena region. Green markers on the map represented spots with affordable PurpleAir sensors purchased and installed by local residents, business proprietors, and community institutions, such as schools, creating a network fostered by citizen science. Data from these sensors also contribute to the EPA’s information, assisting in the development of the air-quality index (AQI) that is reported on weather applications on our smartphones, for instance.
In the immediate aftermath of the fire, Baliaka and Wennberg noticed with alarm that the PurpleAir map was entirely void of sensors in the Altadena burn zone. All the sensors had either been destroyed or were no longer receiving the Wi-Fi and utility power essential for their operation.
“This represented a significant loss of critical data for the entire community,” Wennberg remarks. “All those PurpleAir sensors had simply vanished.”
Simultaneously, the researchers were reviewing data from the ASCENT (Atmospheric Science and Chemistry mEasurement NeTwork) site that Baliaka helped establish in Pico Rivera. The array of instruments there is part of a nationwide network of 12 aerosol measuring stations managed by Nga Lee (Sally) Ng (PhD ’07) of Georgia Institute of Technology. The Pico Rivera ASCENT site was recording increased levels of toxins such as lead and chlorine in the fine particulate matter in the air being carried downwind from the fire.
“We were examining Haroula’s data, observing all this lead within the particulates in the air, and contemplating what measures we could take to aid our community,” Wennberg states.
Thus, 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), inquired among faculty in the division regarding fire-related projects requiring immediate financial backing, Wennberg, a GPS faculty member, swiftly sent an email. Thanks to contributions from members of the GPS Chair’s Advisory Council and other supporters of the GPS division, along with backing from the Resnick Sustainability Institute, the team swiftly secured sufficient funds to acquire the initial set of sensors. Additional loans of sensors for the network have been provided by JPL, the Georgia Institute of Technology, and the ASCENT network. The City of Pasadena is also acquiring a sensor for installation on the roof of a Public Health Department building. QuantAQ generously donated a year of service contract for the operation of Caltech’s sensors for the two-year period. Looking forward, the team aims to further expand the network and enhance the public database to deliver real-time access to particulate matter levels.
“Everything fell into place so rapidly,” Wennberg remarks. “This seemed like an area where we could genuinely assist the community. Yet it was truly Haroula who asserted, ‘We must do this.’