Wildfire smoke

Potential wildfire smoke exposures have risen in California with more frequent and severe wildfires.

As a warming climate fuels wildfires in California, human and environmental exposures to harmful air pollutants are increasing. Wildfire smoke is a complex mixture of toxic gases, fine particulate matter, and other pollutants linked to respiratory illnesses and other health effects. Scientists can estimate potential population exposures using satellite imagery of smoke plumes. Satellite-detected smoke plumes often co-occur with higher concentrations of fine particulate matter (2.5 microns or less in diameter, or PM2.5). For more information, download the Wildfire Smoke chapter.

Smoke plumes from the Camp Fire, the deadliest and most destructive wildfire in California’s history. 

Source:CAL FIRE

What does the indicator show?

Potential population exposures* to wildfire smoke, 2010-2023

This graph presents “person days,” or the estimated number of people living where smoke plumes were present, multiplied by the number of days when the plumes were present.

Number of wildfire smoke days by California county

Maps present the number of days when smoke plumes were present in each county each year.

• Since 2010, potential population exposures to wildfire smoke have been increasing in California, peaking in 2020.
• In 2020, smoke plumes covered every county for at least 46 days; by contrast, from 2010 to 2014, only 11 counties had at least 46 days on average each year. A record-high 4.2 million acres burned in 2020, and several large wildfires burned at once, leading to unprecedented air quality impacts.

• Exposures to wildfire smoke can lead to harmful health effects, especially among people with underlying health conditions, the elderly, children, pregnant people, and lower-income groups. Wildland firefighters are especially at risk, as are agricultural workers. During the 2017 Thomas Fire, thousands of farmworkers continued working in the fields to prevent crop loss from smoke and ash.
• Wildfire smoke can impact air quality many miles from the fire location. In 2020, wildfire smoke in California, Oregon, and Washington reached the eastern United States.
• Wildfire smoke can increase business costs, affect job productivity, reduce earnings, and impact tourism and outdoor recreation.

In 2020, a jet stream transported wildfire smoke in California, Oregon, and Washington eastward across the United States. This video shows average carbon monoxide concentrations (measured by satellite infrared sensors) in the atmosphere due to wildfires from September 6 to 14, 2020. As of September 14, almost 90 large wildfires were burning in the western US; 28 were in California, including the August Complex Fire, which burned over a million acres. Red and orange regions depict higher concentrations of carbon monoxide. 

Credit: NASA/JPL-Caltech

• Wildfires are happening more often and becoming more extreme due to conditions exacerbated by climate change. Among these factors are warmer temperatures, reduced precipitation and snowpack, drought, and tree deaths.
• The extent and duration of wildfire smoke are impacted by the size, severity, and duration of the fires as well as wind and weather patterns.

• Air Now, U.S. Air Quality Index
• CAL FIRE, Incident Information
• California Air Resources Board, Wildfires
• California Department of Public Health, Emergency Preparedness, Wildfires
• National Oceanic and Atmospheric Administration (NOAA), Hazard Mapping System Fire and Smoke Product
• Office of Environmental Health Hazard Assessment, Wildfires
• US Environmental Protection Agency (USEPA), Wildfire Smoke: A Guide for Public Health Officials