Evolution of Reactive Organic Compounds and Their Potential Health Risk in Wildfire Smoke

Creators: Pye, Havala O. T.¹; Xu, Lu²; Henderson, Barron H.¹; Pagonis, Demetrios^{3, 4}; Campuzano-Jost, Pedro^{3, 5}; Guo, Hongyu^{3, 5}; Jimenez, Jose L.^{3, 5}; Allen, Christine⁶; Skipper, T. Nash¹; Halliday, Hannah S.²; Murphy, Benjamin N.¹; D'Ambro, Emma L.¹; Wennberg, Paul O.⁷; Place, Bryan K.¹; Wiser, Forwood C.⁸; McNeill, V. Faye⁸; Apel, Eric C.⁹; Blake, Donald R.¹⁰; Coggon, Matthew M.; Crounse, John D.⁷; Gilman, Jessica B.; Gkatzelis, Georgios I.³; Hanisco, Thomas F.¹¹; Huey, L. Gregory¹²; Katich, Joseph M.³; Lamplugh, Aaron³; Lindaas, Jakob¹³; Peischl, Jeff³; St Clair, Jason M.^{11, 14}; Warneke, Carsten; Wolfe, Glenn M.¹¹; Womack, Caroline

1. Environmental Protection Agency
2. Washington University in St. Louis
3. Cooperative Institute for Research in Environmental Sciences
4. Weber State University
5. University of Colorado Boulder
6. GDIT, Durham, North Carolina 27709, United States.
7. California Institute of Technology
8. Columbia University
9. National Center for Atmospheric Research
10. University of California, Irvine
11. Goddard Space Flight Center
12. Georgia Institute of Technology
13. Colorado State University
14. University of Maryland, Baltimore County

Abstract

Wildfires are an increasing source of emissions into the air, with health effects modulated by the abundance and toxicity of individual species. In this work, we estimate reactive organic compounds (ROC) in western U.S. wildland forest fire smoke using a combination of observations from the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign and predictions from the Community Multiscale Air Quality (CMAQ) model. Standard emission inventory methods capture 40–45% of the estimated ROC mass emitted, with estimates of primary organic aerosol particularly low (5–8×). Downwind, gas-phase species abundances in molar units reflect the production of fragmentation products such as formaldehyde and methanol. Mass-based units emphasize larger compounds, which tend to be unidentified at an individual species level, are less volatile, and are typically not measured in the gas phase. Fire emissions are estimated to total 1250 ± 60 g·C of ROC per kg·C of CO, implying as much carbon is emitted as ROC as is emitted as CO. Particulate ROC has the potential to dominate the cancer and noncancer risk of long-term exposure to inhaled smoke, and better constraining these estimates will require information on the toxicity of particulate ROC from forest fires.

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Additional Information

Special Issue: Published as part of Environmental Science & Technology special issue “Wildland Fires: Emissions, Chemistry, Contamination, Climate, and Human Health”.

Funding

This work was supported by the U.S. Environmental Protection Agency. P.O.W., L.X., and J.D.C. acknowledge NASA grant 80NSSC21K1704. L.X., M.M.C., G.I.G., A.L., J.P., and C.W. were supported in part by NOAA cooperative agreement NA17OAR4320101. D.P., H.G., P.C.-J., and J.L.J. acknowledge support from NASA Grants 80NSSC23K0828 and 80NSSC21K1451 and NSF AGS 2206655. G.M.W., J.M.S., and T.F.H. acknowledge support from the NASA Tropospheric Composition Program and NOAA Climate Program Office’s Atmospheric Chemistry, Carbon Cycle and Climate (AC4) program (NA17OAR4310004).

Acknowledgement

The authors thank the NOAA Black Carbon Group for providing measurement data. The authors thank Jeff Pierce, Rob Pinder, Jason Lambert, Jason Sacks, James Beidler, Stephen MacFarlane, and Jenny Fisher for useful discussion. The authors thank the FIREX-AQ and CMAQ teams for making data and code publicly available. The views expressed in this article are those of the authors and do not necessarily reflect the views or polices of the U.S. EPA.

Contributions

The manuscript was initially drafted by H.O.T.P. and edited and reviewed by all authors. L.X., D.P., P.C.-J., H.G., J.L.J., P.O.W., E.C.A., D.R.B., M.M.C., J.D.C., J.B.G., G.I.G., T.F.H., L.G.H., J.M.K., A.L., J.L., J.P., J.M.S., C.W., G.M.W., and C.W. contributed measurement data. C.A. contributed emission data. H.O.T.P., B.H.H., T.N.S., B.N.M., E.L.D., F.C.W., and V.F.M. contributed code. All authors have given approval to the final version of the manuscript.

Data Availability

Analysis scripts and intermediate data files will be available at data.gov (doi: 10.23719/1531092).

FIREX-AQ measurement data is available at https://www-air.larc.nasa.gov/cgi-bin/ArcView/firexaq.

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