Caltech Expert Tells City Council Air Quality Returning to Normal After Eaton Fire, City Eyes Enhanced Monitoring

At a special Pasadena City Council meeting Thursday, a Caltech atmospheric chemistry expert assured members that local air quality has largely normalized following the Eaton Fire, even as local officials consider deploying additional monitoring equipment across affected neighborhoods.

“And so the good news is that the amounts of lead and other indicators of ash and dust in the air now this is in the particles smaller than 2.5 microns, suggest that the mobility of the ash and dust has not affected air quality terribly downwind of Altadena,” said Paul Wennberg, the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering at Caltech.

The Environmental Protection Agency regulates both fine particulate matter smaller than 2.5 microns (PM 2.5), which can be deposited deep in the lungs, and particles under 10 microns (PM 10) that tend to deposit higher in the respiratory system.

During the special meeting focused on environmental monitoring and testing, Pasadena Public Health Acting Director Manuel Carmona presented plans to potentially expand the city’s network of “Purple Air” sensors, which provide real-time neighborhood-level air quality data. Current sensor coverage shows gaps, particularly in northern Pasadena.

Wennberg noted that measurements using both the Purple Air Network and South Coast Air Quality Management District sensors indicate particulate matter levels have been “historically low compared to the previous few weeks.”

He explained this week’s good visibility reflects improved conditions, aided by northerly winds bringing cleaner desert air.

However, officials noted Purple Air sensors can get contaminated and give false readings, with accuracy diminishing during extreme events like wildfires. Each sensor costs about $300.

Wennberg recommended adding sensors at Pasadena Unified School District sites, suggesting it could serve both monitoring and educational purposes.

He also advised against using leaf blowers, which can re-disturb settled particles.

On January 15, the City announced the prohibition of power air blowers and air-propelling devices (such as leaf blowers) until further notice to help limit the negative health impacts of fire ash, smoke, and particulate matter.

Wennberg also explained that while poor air quality measurements don’t necessarily indicate toxins are present, they suggest potential presence. He noted that fire-related gases can penetrate deeply into materials like walls and carpets, recommending that residents ventilate their homes when air quality is good and consider using air cleaners to remove smoke smells.

Carmona emphasized that air quality is a regional rather than purely local issue, with Los Angeles County covering over 4,000 square miles compared to Pasadena’s 23 square miles. He noted that air “flows freely throughout” the region.

The discussion came as part of broader City efforts to assess environmental impacts from the recent Eaton Fire, which burned 14,021 acres and is now 95% contained according to fire officials.

The City plans to continue discussions with agencies and public health partners to develop a regional approach for air quality monitoring and testing.