Indoor and outdoor volatile organic compound levels during and after the 2025 Los Angeles wildfires

Abstract

The January 2025 Los Angeles wildfires released large amounts of air pollutants and exposed millions of residents to smoke containing hazardous volatile organic compounds (VOCs). To assess exposure risks, we conducted indoor and outdoor VOCs sampling at 22 households near the Palisades and Eaton Fires across three phases: active burning with less than 50% containment (January 8–15), active burning period with more than 50% containment (January 24–31), and postfire (February 11–18). Outdoor benzene concentrations peaked during Phase 1, with a median (interquartile range) of 0.38 (0.27) ppb, decreased over time, and remained below the California Office of Environmental Health Hazard Assessment health benchmarks. Compared with the active burning period, indoor-to-outdoor ratios of m,p-xylene (p = 0.004), carbon tetrachloride (p = 0.002), and heptane (p = 0.02) were significantly higher in the postfire period. Elevated VOC levels were particularly evident in uninhabited homes within burn zones, suggesting ongoing indoor emissions from smoke-impacted materials. These findings raise concerns about indoor air quality postwildfire and the potential for prolonged exposure, underscoring the need for targeted mitigation and ongoing monitoring to protect public health during recovery.

Key Findings

• Phase-dependent VOC concentrations: Outdoor benzene concentrations peaked during early active burning phase (0.38 ppb median) and declined through subsequent phases
• Indoor persistence: Indoor-to-outdoor ratios of several VOCs (m,p-xylene, carbon tetrachloride, heptane) were significantly higher in the postfire period compared to active burning
• Burn zone impacts: Elevated VOC levels were particularly evident in uninhabited homes within burn zones, suggesting ongoing emissions from smoke-impacted materials
• Health implications: Despite elevated levels, outdoor VOC concentrations remained below California OEHHA health benchmarks

Public Health Significance

This research demonstrates that wildfire smoke impacts on indoor air quality can persist well beyond fire containment, with important implications for residents returning to fire-affected areas. The study provides critical data for developing targeted interventions to minimize indoor exposures during wildfire recovery phases.

Media Coverage

This research has received significant media attention highlighting the unexpected persistence of indoor air quality issues after wildfires:

• Featured in major outlets including the Washington Post, Associated Press, Los Angeles Daily News, and UCLA Newsroom
• Contributed to public understanding of post-wildfire health risks and recovery planning

Recommended citation: Yao, Y., Garcia-Gonzales, D., Li, J., Niu, M., Nie, Q., Jerrett, M., & Zhu, Y. (2026). Indoor and Outdoor Volatile Organic Compound Levels during and after the 2025 Los Angeles Wildfires. Environmental Science & Technology Letters, 13, 70–75.
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