Wildfires Pollute Much More Than Previously Thought

The Science

Biomass burning, which includes wildfires and prescribed agricultural and forest management burns, is a large global emission source of trace gases and aerosol particles to the atmosphere. In the United States, wildfires are the largest contributor to the annual total area burned and occur largely in the western continental states and Alaska. Understanding the types and amounts of gases and particles produced by wildfires is important for understanding their overall impacts on air pollution and human health. Previous aircraft studies of U.S. forest fire emissions have been performed primarily on controlled burns. In this study, scientists, including researchers from Los Alamos, Brookhaven, and Pacific Northwest national laboratories, used research aircraft operated by the Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility and National Aeronautics and Space Administration (NASA) to study details of fresh emissions from the initial stages of three western U.S. wildfires.

The Impact

This research quantifies the emissions of a range of both gaseous and particulate species from U.S. wildfires using measurements performed on research aircraft operated by DOE and NASA. The results indicate that wildfires are a large source of particulate pollution in western states and that the source is currently underestimated by more than a factor of three in emissions inventories. Comparison of these results to those obtained from prescribed burning indicates that wildfires are a larger source of pollution. These findings could better inform fire management and support the practice of prescribed burning to reduce the impact of particulate matter from wildfires on air quality.

Summary

Plumes from three wildfires in the western United States were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors for over 80 gases and five components of submicron particulate matter (PM1) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed emission factors are compared with previous measurements of temperate wildfires, boreal forest fires, and temperate prescribed fires. The wildfires emitted high amounts of PM1 (with organic aerosol dominating the mass) with an average emission factor that is more than two times the emission factors for prescribed fires. The measured emission factors were used to estimate the annual wildfire emissions of carbon monoxide, nitrogen oxides, total non-methane organic compounds, and PM1 from 11 western U.S. states. The estimated gas emissions are generally comparable with the 2011 National Emissions Inventory (NEI). However, the PM1 emission estimate in this study is over three times that of the NEI PM2.5 estimate and is also higher than the PM2.5 emitted from all other sources in these states in the NEI. This study indicates that the source of organic aerosol from biomass burning in western states is significantly underestimated. In addition, the results indicate that prescribed burning may be an effective method to reduce fine particle emissions.

Principal Investigator(s)

Greg Huey
Georgia Tech
[email protected]

Manvendra Dubey
Los Alamos National Laboratory
[email protected]

Funding

This work was supported by National Aeronautics and Space Administration (NASA) grants NNX12AB77G, NNX15AT90G, NNX12AC06G, and NNX14AP46GACCDAM. The BBOP project was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Atmospheric Radiation Measurement (ARM) Climate Research Facility and Atmospheric System Research program. P.C.J., D.A.D., B.B.P., and J.L.J. were supported by NASA NNX12AC03G and NNX15AT96G. M. Müller received additional support from the Austrian Space Applications Programme.

References

Liu, X., et al. 2017. “Airborne Measurements of Western U.S. Wildfire Emissions: Comparison with Prescribed Burning and Air Quality Implications,” Journal of Geophysical Research: Atmospheres 122(11), 6108-29. DOI: 10.1002/ 2016JD026315.