Wildfires are no longer just a problem for remote forests—they’re burning in urban areas like Pacific Palisades and Altadena near Los Angeles, creating toxic smoke filled with harmful chemicals. From homes and vehicles to plastics and construction materials, the fuel in urban wildfires unleashes a dangerous cocktail of pollutants that can pose significant risks to human health.

Urban wildfire smoke: No ordinary pollutant

When wildfires occur in cities, the materials burned release far more than soot and ash—which is a mixture of all different size particles composed of different materials.

Burned vegetation, vehicles, plastics, and building materials produce particulate matter and a variety of toxic compounds, including volatile organic compounds (VOCs) and metals like lead and arsenic.

Researchers in Southern California found that PM2.5 (particles measuring 2.5 microns in diameter or less that can penetrate deeply into the lungs and enter the bloodstream, increasing the risk of respiratory and cardiovascular diseases) from urban wildfires is up to 10 times more harmful to human health compared to PM2.5 from other pollution sources (1).

What makes urban wildfire smoke so toxic?

Urban wildfire smoke is more dangerous than smoke from forest fires because of the variety of materials burned. Homes, cars, and infrastructure release toxic compounds like:

• Polycyclic aromatic hydrocarbons (PAHs): Known to cause cancer and damage the immune system.
• Dioxins and furans: Byproducts of burning plastics and other materials, linked to reproductive and developmental issues.
• Heavy metals: Materials like lead, arsenic, and chromium are released when metals and paints burn, posing risks of neurological and cardiovascular diseases.

Lingering urban wildfire smoke mixes with other particle pollutants, amplifying long-term health risks.

The health impacts of urban wildfire smoke

Urban wildfire smoke can harm your health both immediately and over time:

• Short-term effects include coughing, throat irritation, difficulty breathing, and itchy eyes.
• Long-term effects from chronic exposure can include heart disease, stroke, lung cancer, and even neurological issues.

Vulnerable populations, including children, older adults, pregnant people, and individuals with pre-existing conditions like asthma or heart disease, are at an even higher risk.

Mental health effects

Wildfires don’t just harm physical health—they also take a mental toll. Residents in fire-affected areas report higher rates of depression, anxiety, and post-traumatic stress disorder (PTSD), which can persist for years (2). The stress of displacement, loss of property, and ongoing exposure to poor air quality contributes to these long-term effects.

Why urban wildfire smoke is hard to predict

The chemistry of urban wildfire smoke is highly complex and depends on several factors, including:

• What burns: Different materials—like trees, vehicles, or buildings—release a wide range of pollutants, from natural compounds to toxic chemicals.
• How it burns: Higher temperatures produce more harmful secondary pollutants like ozone.
• How far the smoke travels: Sunlight and other pollutants can alter the composition of wildfire smoke as it disperses.

Researchers found that urban wildfire smoke contains up to 1,000 times more toxic compounds than smoke from natural vegetation fires, underscoring the dangers of city-based blazes.

Lingering effects after the smoke clears

Even after the smoke has disappeared, harmful pollutants often remain in the environment. Ash from urban wildfires can contaminate soil and water supplies with PAHs and heavy metals, while toxic compounds can linger in homes for weeks or even months (3).

A study following the 2021 Marshall Fire in Colorado found high levels of PAHs in ash and VOCs in indoor air samples, both of which are linked to respiratory, developmental, and reproductive health problems. Toxic pollutants were also found in nearby residences’ tap water (4). 

How to protect yourself from urban wildfire smoke

Whether you’re living near an active fire zone or experiencing wildfire smoke carried by the wind, there are simple steps you can take to protect your health:

1. Stay informed: Use an air quality monitor or app to track PM2.5 levels in your area.
2. Wear a mask outdoors: Use a properly fitted mask to filter out harmful particles.
3. Create a clean indoor environment:
   • Run a high-efficiency air purifier in frequently used rooms.
   • Seal doors and windows to keep outdoor air out.
4. Avoid disturbing ash: When cleaning up ash, wear goggles, gloves, long-sleeved shirts, long pants, and shoes. Lightly mist ash with water, then sweep gently with a broom or wet mop. Do not use leaf blowers.
5. Prepare for fire season:
   • Install HEPA filters in your HVAC system.
   • Stock up on masks and ensure you have emergency supplies ready.

The takeaway

Urban wildfire smoke isn’t just an inconvenience—it’s a toxic threat to public health that requires attention and action. Protecting yourself and your family involves staying informed, improving indoor air quality, and taking proactive measures during wildfire season.

As urban wildfires become more common due to climate change, it’s critical to advocate for stronger fire prevention measures and invest in technology that can monitor and mitigate air pollution. Together, we can build healthier, more resilient communities.