Initial findings from PHOENIX:

  1. Dust levels across the zone are generally low and do not exceed EPA regulatory limits (24-hour averages of PM2.5 and PM10 are both within good and moderate levels).

  2. Elevated dust levels are observed along major N-S roadways often in the early morning. As an example, Figure 1 shows data from one of our sensors on N. Fair Oaks Avenue.

Figure 1 Particulate matter (PM10) concentrations in μg/m3 recorded every minute throughout the day from February 26th to April 27th 2025 by a PHOENIX sensor located on N. Fair Oaks Avenue. Colors represent different PM10 concentration levels.
  1. To better understand the composition of the road dust in these areas, we collected dust samples on April 22nd along N. Fair Oaks Avenue in Altadena. These samples were analyzed using Inductively Coupled Plasma Mass Spectrometry at Caltech. Our preliminary findings indicate elevated levels of lead (Pb) in most samples (see Figure 2). Notably, six out of ten samples exceeded 80 ppm which is the California Human Health Screening Level (CHHSL) for residential soil.
Figure 2 Lead (Pb) levels in ppm in dust samples collected along N. Fair Oaks Avenue in Altadena. For reference, typical crustal Pb levels are approximately 17 ppm, and urban soil concentrations are generally below 80 ppm.
  1. While we cannot directly connect the PM10 to the road dust, our observations suggest that resuspension of Pb-containing dust could be occurring, especially in the early morning. This raises concern that occupied properties along these roadways may be experiencing continuing contamination.

We do not know the source of the elevated PM10 or the dust we have sampled along the roadway. We suggest that LA County undertake a study to evaluate the source(s) and causes for elevated levels. These potentially include street sweeping with insufficient dust control; resuspension of dust deposited during the night by the morning traffic; or emissions from uncovered and dirty trucks arriving in the morning.

Even prior to having a more complete understanding of the source of the Pb, our observations suggest that the Altadena public in and around the burn zone be reminded to minimize the tracking of dust indoors, sealing up windows and doors, using proper wet methods for cleaning their homes and increasing the frequency of cleaning — especially for people with young children and pets.