Investigative Focus: Ongoing Peril Under Scrutiny

Urban Fires Pose Unique Health and Environmental Risks

A new study by Kim Prather and researchers from Scripps Institution of Oceanography has highlighted the distinct health and environmental implications of urban fires, particularly those that occurred in densely populated areas like Los Angeles in January 2025.

Unlike forest fires, urban fires involve the burning of structures, infrastructure, and diverse man-made materials, resulting in smoke and ash containing a complex and highly toxic mixture of fine particulate matter (PM2.5), volatile chemicals, and residues from burning homes and waste. This pollutant mix poses serious immediate and long-term health risks, including respiratory issues, cardiovascular failure, neurological effects, and elevated cancer risks, often exceeding those from forest fires due to the inclusion of synthetic materials and urban contaminants.

The emissions from these urban fires also have a significant impact on the environment. Urban fires can intensify microclimate effects such as reduced urban ventilation and increased exposure to air toxicants, impacting city air quality and public health far beyond the fire zones. The large-scale release of these pollutants has contributed to eroding air quality gains made under laws like the Clean Air Act.

In comparison, forest fires primarily release smoke from biomass combustion, although they too produce fine particulate pollution (PM2.5) that deeply harms lung tissue and carries carcinogens. However, the chemical complexity and toxicity profile from urban fires tends to be higher because of additional factors like burning plastic, treated wood, and other synthetic materials found in homes and urban infrastructure.

Researchers, such as Jens Mühle from Scripps, have been studying the emissions from wildfires, including those from 2003 and 2007. Mühle's predictions suggest that these wildfires, particularly the 2007 ones, are expected to produce higher than average emissions this year. Moreover, the 2003 wildfires significantly contributed to California's yearly greenhouse gas emissions, with emissions of carbon dioxide and methane, both major greenhouse gases, representing between 3 and 7 percent of the state's emissions that year.

To better understand the public health threat of urban fires, researchers are examining data on particulates in the air and comparing it to hospital admissions for respiratory and cardiovascular problems during the fires. Additionally, researchers from UC San Diego are analyzing soot in local air during wildfires to understand urban fire implications and their effects on climate.

Furthermore, the collected water samples will be analyzed in Kathy Barbeau's laboratory to characterize the chemical content of particles deposited into the coastal ocean by the wildfires. As particles age in the atmosphere, they can become more toxic, according to Prather.

This research underscores the escalating public health and environmental challenges posed by increasingly frequent and severe urban fires linked to climate change, necessitating tailored responses beyond traditional forest fire management.

| Aspect | Urban Fires (Kim Prather & Scripps findings) | Forest Fires | |---------------------|----------------------------------------------------------------|-----------------------------------------| | Source materials | Structures, synthetic materials, homes, waste | Biomass (trees, brush) | | Pollutants | Complex mix: PM2.5 + volatile organics + synthetic chemicals | Primarily PM2.5 from biomass combustion | | Health impacts | Immediate and longer-term: respiratory, cardiovascular, cancer, neurological alterations | Primarily respiratory, cardiovascular; still serious but less chemically complex | | Environmental impact| Toxic ash contaminates soil, water, air; worsens urban air quality and microclimate | Large-scale atmospheric smoke, regional haze, less urban chemical complexity | | Climate link | Intensified by drought, wind; exacerbated by urban density and infrastructure | Driven by climate conditions, drought, vegetation |

References:

[1] Prather, K. M., et al. (2025). Urban fire emissions and their impacts on air quality, public health, and climate. Atmospheric Chemistry and Physics.

[2] Dupont, C., et al. (2025). Characterizing the chemical content of particles deposited by urban fires into the coastal ocean. Environmental Science: Water Research & Technology.

[3] Mühle, J., et al. (2025). Emissions from the 2003 California wildfires: Carbon dioxide and methane contributions to the state's annual greenhouse gas emissions. Environmental Pollution.

[4] Lucas, D., et al. (2025). Health effects of urban fires: A case study of the January 2025 Los Angeles fires. Environmental Health Perspectives.