The LA Fire HEALTH Study today released preliminary* air quality data for the Los Angeles area during the Palisades and Eaton wildfires in January 2025. The data shows how outdoor levels of particulate matter (PM) impacted air quality inside of homes during the wildfires. 

This data brief includes findings from Harvard Healthy Buildings and Airthings—a technology company that specializes in indoor air quality monitors for homes, workplaces, and schools—to study how the LA wildfires affected indoor air quality in nearby homes, using real-time data from 1,578 Airthings monitors installed in 1,048 homes across Los Angeles.  

This data is an important step to understanding the real-time impacts of wildfires on the health of residents, the effectiveness of in-home air quality monitors, and how the air inside of homes can be impacted by outdoor air quality. 

Key Takeaways: 

• LA Wildfires led to elevated PM_2.5 levels in homes. Homes located throughout Los Angeles saw an increase in indoor PM correlated with elevated outdoor levels at the time of the LA fires.  
• LA Wildfires impacted home air quality in areas away from the burn zone. The impact of the wildfires extended to homes located more than two miles from the burn area.  
• Real-time air monitors may be useful for wildfire response:  
• Indoor air quality sensors worked well at detecting changes in home PM concentrations during the wildfires, in real time.  
• Monitoring indoor air quality and taking informed precautions (such as wearing N-95 masks, using air filters, closing windows, etc.) are vital to protect health during wildfires and other events that increase outdoor particulate matter. 

Previous data briefs examined indoor and outdoor air quality in the days since the fire, in both the Palisades and Eaton areas.  

Those findings indicated that: 

• Outdoor air quality in the weeks after the fire was generally within EPA health-based guidelines and consistent with overall Los Angeles air quality. (View Data Brief 1) 
• Indoor air, particularly in homes located in the burn zone and homes that sustained partial or minor damage, contained higher concentrations of particulate matter and Volatile organic compounds (VOCs). (View Data Brief 2) 
• Continued caution is advised when inside homes in the burn area, especially during cleaning activities. These precautions include: 
  • Using HEPA air filtration systems (portable room cleaners and/or MERV-13 or higher filters on HVAC and AC systems) whenever possible. 
  • Wearing PPE, especially while cleaning fire debris, ash, and dust. 
  • Ventilating homes to allow contaminants to escape, and also shutting windows when there is nearby debris removal to prevent more toxins from entering the home.  
  • Learn more about recommended precautions here: https://lafirehealth.org/faq/ 

These data briefs are part of a larger study of air, water, dust, and soil in the vicinity of the Palisades and Eaton Fires. Additional testing is underway and will be reported publicly as the data are reviewed by the research team.  

About the LA Fire HEALTH Study 

The Los Angeles Fire Human Exposure and Long-Term Health (HEALTH) Study is a 10-year study of the January 2025 Eaton and Palisades wildfires to evaluate which pollutants are present, at what levels and where, and to assess the health impacts of the wildfires.  

This multi-institutional consortium study is a collaboration between researchers from Harvard T.H. Chan School of Public Health, the Keck School of Medicine of USC, Stanford University, the UCLA Fielding School of Public Health, the University of California at Davis, the University of Texas at Austin, and Yale University. Learn more: https://lafirehealth.org/about/ 

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*Important disclaimer: The data shared in this brief are preliminary in nature and are being made available to the public in an effort to provide data as soon as possible. Research is a process and results can change over time based on new data input. The data shared on this site is for informational use only and should not replace the advice of a medical professional. This is a study run by a consortium and as such, no one university or institution is responsible or liable for the data or recommendations presented.