Wildland Fire Research: What’s in Smoke?
Because the pollutants in smoke vary with the fuel that is burned, EPA researchers have developed, tested, and applied air measurement technologies to understand smoke emissions and to measure the concentrations of pollutants from different types of fires.
The growth of the wildland-urban-interface (WUI) can mean instances of wildfire burning human-made structures and materials. The emissions from WUI fires can potentially contain greater amounts of hazardous air pollutants. The combination of more toxic emissions and the proximity to population centers makes WUI fires a unique threat to public health.
On this page:
- Smoke from WUI Fires: Chemical Composition
- Smoke from WUI Fires: Estimate Smoke Emissions
- Smoke from Different Forest Types: Quantifying Smoke Emissions
- EPA’s Wildfire Smoke Emissions Inventory
- Future Directions
Smoke from WUI Fires: Chemical Composition
What chemicals are emitted during wildland fires? We want to understand what is in smoke so we can better communicate appropriate actions that reduce the risks to public health.
When examining measurements of particulate matter from four historic fires, researchers found that all types of fires produce certain chemicals, such as magnesium, aluminum, and calcium, and many of these were statistically elevated on smoke-impacted days in over half of the years studied. However, WUI fires appear to have a unique chemical profile. Smoke from WUI fires contains other chemicals, mostly trace metals that are harmful to human health, including copper, lead, and zinc. Elevated concentrations of these metals were associated with the burning of structures; for instance, in 2018, lead was more than 40 times higher on smoke days, on average, at the Point Reyes monitoring station, likely attributable to the Camp Fire burning approximately 200 kilometers away.
The difference in the chemical composition of smoke, specifically an increase in toxic metals due to structural burning, has potential implications for public health and ecosystems, especially in downwind communities.
Wildfires Increase Concentrations of Hazardous Air Pollutants in Downwind Communities (2023)
Smoke from WUI Fires: Estimate Smoke Emissions
How different is smoke from a WUI fire burning human-made structures compared to smoke from a “normal” wildfire burning natural vegetation?
WUI fires can be a sizeable source of certain hazardous air pollutants. Researchers developed emission factors (EFs) that relate the quantity of a pollutant emitted with a burning activity to improve estimates of the emissions from WUI fires versus wildfires. The EFs for some toxic compounds like polycylic aromatic hydrocarbons (PAH) and toxic organic compounds were 5 –2,500 times greater for WUI fires than those from natural fuels.
As WUI fires are a potential major source of hazardous air pollutants, EPA work is a critical first step to improving emissions inventories, which, until now, had not included structural fires. A better understanding helps guide future measurement efforts, develop emissions inventories (detailed estimates of emissions into the air), and inform the public about health risks.
Hazardous air pollutant emissions estimates from wildfires in the wildland urban interface (2023)
Smoke from Different Forest Types: Quantifying Smoke Emissions
How can we evaluate smoke emissions for different prescribed fire and wildfire scenarios in the western U.S.?
EPA performed laboratory experiments for emission factors (EFs) that relate the quantity of air pollutant emissions in the smoke to the fire scenario. With accurate EFs we can estimate emissions for a particular activity, which helps us make decisions about the impacts of smoke on public health and build a national inventory of emissions.
The study addressed gaps in EFs for two forest types - Douglas fir canopy fuels, and black spruce/jack pine surface fuel – that are a significant part of western U.S. forests and was the first to quantify EFs for cones from ponderosa pine, an important component of the litter layer. With this knowledge, we can evaluate the consequences of the emissions due to different land management strategies, such as prescribed fires. This information helps land management agencies understand the public health impacts of the smoke emissions from prescribed fires vs. wildfires.
EPA’s Wildfire Smoke Emissions Inventory
How can we accurately estimate emissions – including emissions from wildland fire smoke – so that we can model air quality as it changes over time? Accurate and consistent emission estimates are needed in regional air quality modeling, which we use to study air quality impacts on human health and ecosystems over time spans of decades, as we do in EPA’s National Air Quality Trends reports.
As part of EPA's Air QUAlity TimE Series (EQUATES) Project, EPA researchers developed a consistent set of long-term emissions inputs spanning the years 2002 through 2017.
The EQUATES Project provided a multiyear set of updated emissions data for 14 source categories. Having a consistent set of emissions data, including for fires, is foundational for running simulations of air quality that allow decision makers to explore the effects of air quality management strategies and look at trends over time.
2002–2017 anthropogenic emissions data for air quality modeling over the United States (2023)
Future Directions
EPA researchers developed, tested, and applied emerging air measurement technologies to measure and understand smoke emissions and air quality. The foundation has been laid through mobile monitoring units that can assess real-time smoke conditions in affected areas, remote sensing technologies to aid in the tracking of smoke and using controlled burns in a laboratory setting to estimate emissions generated from actual wildland fires.
- The U.S. is experiencing greater frequency of fires in the wildland-urban interface (WUI) and recent fires have resulted in substantial destruction of buildings and vehicles. Future research is needed to help to improve emission factors related to WUI fires that include the burning of human-made structures and materials.
- While prescribed burns may individually produce less smoke than a wildfire, they may be more frequent and widespread. Future research can help understand the air quality and health impacts of smoke emissions from repeated and simultaneously occurring prescribed fires and develop air quality models to understand the public health impacts of wildland fire smoke from prescribed fires and wildfires over time and across geographic areas.