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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 10 Sep 2019

Submitted as: research article | 10 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Relationship between the molecular composition, visible light absorption, and health-related properties of smoldering woodsmoke aerosols

Lam Kam Chan1, Khanh Q. Nguyen1, Noreen Karim1, Yatian Yang1,a, Robert H. Rice1, Guochun He1, Michael S. Denison1, and Tran B. Nguyen1 Lam Kam Chan et al.
  • 1Department of Environmental Toxicology, University of California Davis, Davis, CA 95616, USA
  • anow at: Department of Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, USA

Abstract. Organic aerosols generated from the smoldering combustion of wood critically impact air quality and health for billions of people worldwide; yet, the links between the chemical components and the optical or biological effects of woodsmoke aerosols (WSA) are still poorly understood. In this work, an untargeted analysis of the molecular composition of smoldering WSA, generated in a controlled environment from nine types of heartwood fuels (African Mahogany, Birch, Cherry, Maple, Pine, Poplar, Red Oak, Redwood, and Walnut) identified several hundred compounds using gas chromatography mass spectrometry (GC-MS) and nano-electrospray high-resolution mass spectrometry (HRMS) with tandem multistage mass spectrometry (MSn). The effects of WSA on cell toxicity, aryl hydrocarbon receptor (AhR)- and estrogen receptor (ER)-dependent gene expression were characterized with cellular assays, and the visible mass absorption coefficients (MACvis) of WSA were measured with UV-visible spectroscopy. The WSA studied in this work have significant levels of biological and toxicological activity, with exposure levels in both an outdoor and indoor environment similar to or greater than those of other toxicants. A correlation between the HRMS molecular composition and aerosol properties found that phenolic compounds from the oxidative decomposition of lignin were the main drivers of aerosol effects, while the cellulose decomposition products played a secondary role, e.g., levoglucosan was anti-correlated with multiple effects. Polycyclic aromatic hydrocarbons (PAHs) were not expected to form at the combustion temperature in this work, nor were observed above the detection limit; thus, biological and optical properties of the smoldering WSA are not attributed to PAHs. Syringyl compounds tend to correlate with cell toxicity, while the more conjugated molecules (including several compounds assigned to dimers) had higher AhR activity and MACvis. The negative correlation between cell toxicity and AhR activity suggests that the toxicity of WSA to cells was not mediated by the AhR. Both mass-normalized biological outcomes had a statistically-significant dependence on the degree of combustion of the wood. In addition, our observations support that the visible light absorption of WSA is at least partially due to charge transfer effects in aerosols, as previously suggested. Finally, MACvis had no correlation with toxicity or receptor signaling, suggesting that key chromophores are not biologically active on the endpoints tested.

Lam Kam Chan et al.
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Lam Kam Chan et al.
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Short summary
Aerosols from the low-intensity combustion of nine types of woods were generated in a controlled laboratory environment and subjected to chemical, physical, and biological/toxicological analysis. We found links between specific compounds and aerosol properties. The aerosol's toxicity is not similar to PAHs or dioxins, and may be related to the degree of combustion of the wood. The aerosol's light absorption is not related to biological activity.
Aerosols from the low-intensity combustion of nine types of woods were generated in a controlled...